# surge-lfo
A Rust crate for generating low-frequency
oscillations (LFOs) for the Surge synthesizer
system. The crate contains a variety of LFO
shapes, including sine, square, triangle, sample
and hold, and step sequencer. The LFO can be set
to free run, key trigger, or random modes, and the
output can be bipolar or unipolar. The crate also
includes an envelope generator that can be used to
shape the LFO output.
Mathematical concepts utilized in the crate
include:
- Low-pass filtering: used in the `Lag` struct to
smooth values over time.
- Trigonometric functions: used to generate LFO
waveforms, such as sine, square, and triangle.
- Sample and hold: a technique that randomly
samples an input signal at regular intervals and
holds that value until the next sample. Used in
the sample and hold LFO shape.
- Step sequencer: a sequence of discrete values
that are stepped through in a repeating
pattern. Used in the step sequencer LFO shape.
The crate provides methods for updating the LFO
state and retrieving its current phase, rate, and
shape. Tests are included to ensure that the LFO
and envelope generator functions as expected.
119> cool thanks! could you describe for me how an
LFO works in mathematical detail?
Sure, I'd be happy to!
An LFO (Low Frequency Oscillator) is an electronic
signal generator that produces a periodic waveform
at a frequency below the audible range, typically
between 0.1 Hz and 20 Hz. It is commonly used in
electronic music to modulate other sound sources
or control parameters of synthesizers and effects
processors.
Mathematically, an LFO can be modeled as
a function that generates a periodic signal with
a specific frequency and waveform shape. The most
common waveform shapes used in LFOs are sine,
square, triangle, sawtooth, and noise.
To generate a periodic signal, the LFO function
needs to keep track of the current phase, which
represents the position of the waveform in its
period. The phase is usually represented as
a value between 0 and 1, where 0 corresponds to
the beginning of the waveform and 1 corresponds to
the end.
The LFO function can be represented as:
f(t) = A * g(2πft + φ)
where f is the frequency of the LFO, A is the
amplitude, g is the waveform shape function
(e.g. sine, square, etc.), t is time, and φ is the
initial phase of the waveform.
The LFO frequency f is typically expressed in
Hertz (Hz), which represents the number of cycles
per second. To generate an LFO signal with
a frequency of 1 Hz, for example, the waveform
needs to complete one cycle (i.e. go from 0 to 1)
in one second.
The waveform shape function g determines the shape
of the LFO signal. For example, a sine wave can be
represented as:
g(t) = sin(t)
while a square wave can be represented as:
g(t) = sign(sin(t))
where sign is the signum function, which returns
-1 for negative values and 1 for positive values.
In addition to the waveform shape, LFOs can also
have other parameters such as phase, symmetry
(duty cycle for square waves), and randomness (for
noise waves).
Overall, LFOs provide a powerful tool for creating
complex and evolving sounds in electronic music by
modulating various parameters over time.
120> cool, thanks! what should we keep in mind
while using them?
Here are some things to keep in mind when using
LFOs:
1. Range: Consider the range of the LFO's output
and whether it will work well with the
parameter you want to modulate. If the LFO's
range is too large or too small, it may cause
undesirable effects or not have a noticeable
effect on the parameter.
2. Rate: The rate of the LFO determines how
quickly it cycles through its
waveform. Consider the rate you want for the
modulation effect you are trying to
achieve. A slower rate may be better for subtle
effects, while a faster rate may be better for
more pronounced effects.
3. Waveform: The waveform of the LFO determines
the shape of the modulation effect. Consider
the waveform you want for the modulation effect
you are trying to achieve. For example, a sine
wave may be better for smooth, subtle effects,
while a square wave may be better for more
rhythmic, choppy effects.
4. Sync: Some LFOs can be synced to the tempo of
the music. Consider whether you want the LFO to
be synced or free-running.
5. Phase: The phase of the LFO determines where it
starts in its cycle. Consider the phase you
want for the modulation effect you are trying
to achieve.
6. Modulation Depth: The modulation depth
determines the amount of modulation applied to
the parameter. Consider the modulation depth
you want for the modulation effect you are
trying to achieve.
7. Bipolar vs Unipolar: Consider whether you want
the LFO to produce modulation in both positive
and negative directions (bipolar) or only in
the positive direction (unipolar).
8. Key trigger vs Free run: Consider whether you
want the LFO to restart its cycle on each note
trigger (key trigger) or continue its cycle
from its current phase (free run).
121> how do we get it so that the lfo feels like
it is free running for a little while, but then
locks back on to a distinct rhythmic, synced
frequency?
One way to achieve this effect is to use
a combination of two LFOs with different
rates. The first LFO is set to free running mode
and its rate is set relatively slow. This LFO is
used to generate a random or drifting waveform
that feels free-running. The output of this LFO is
then used to modulate the frequency of the second
LFO, which is set to a faster rate and synced to
the tempo of the music.
The second LFO will now follow the modulations of
the first LFO and move around its original synced
frequency. This creates the illusion of the LFO
being free running for a while, but then locking
back on to a distinct rhythmic, synced frequency.
Another approach is to use an LFO with a random or
chaotic waveform that drifts around a central
frequency, and then use a sample and hold circuit
to quantize the output of the LFO to a grid of
rhythmic values. The sample and hold circuit will
periodically capture the output of the LFO and
hold it until the next trigger signal arrives,
which creates the rhythmic pattern.
The rate of the trigger signal can be synced to
the tempo of the music, and the frequency of the
chaotic LFO can be modulated by an envelope
generator or another LFO to create different
rhythms and patterns over time. This approach can
create a more unpredictable and evolving rhythmic
pattern that feels like it is free running for
a while, but then locks back on to a distinct
rhythmic, synced frequency.
122> what are some other techniques we can use
when working with lfos?
Here are some other techniques that can be used
when working with LFOs:
1. Modulation: LFOs can be used to modulate other
parameters, such as filter cutoff, amplitude,
or pitch. By modulating these parameters, you
can create interesting and evolving sounds that
change over time.
2. Sync: LFOs can be synced to the tempo of the
song, which can create rhythmic patterns that
fit within the context of the music. This can
be achieved by dividing the tempo of the song
by a specific number of steps or by using
a sync option in your software or hardware.
3. Shape: LFOs can have different wave shapes,
including sine, square, triangle, and
sawtooth. By using different shapes, you can
create different types of modulation, such as
smooth fades or sharp jumps.
4. Rate: LFOs can be set to different rates, which
can create different speeds of modulation. By
adjusting the rate, you can create slow and
evolving sounds or fast and rhythmic patterns.
5. Amplitude: LFOs can be used to modulate the
amplitude of another LFO, which can create
complex and evolving patterns.
6. Envelope Follower: LFOs can be used as an
envelope follower, which means that they
respond to the level of the audio signal. By
using an envelope follower, you can create
modulation that is synced to the rhythm of the
music and responds to the dynamics of the audio
signal.
Overall, LFOs are a versatile tool that can be
used in many different ways to create interesting
and evolving sounds. By experimenting with
different shapes, rates, and modulation targets,
you can create unique sounds that add depth and
movement to your music.
123> what are some more advanced techniques?
There are several more advanced techniques that
can be used when working with LFOs, some of which
are:
1. Waveform shaping: By applying a function to the
LFO waveform, it is possible to transform the
shape of the waveform into more complex
shapes. For example, using a waveshaper
function like a sine waveshaper can convert
a triangle waveform into a smoother, more
rounded shape. This can result in interesting
and unique modulation effects.
2. Phase distortion: By adding distortion to the
phase of an LFO waveform, it is possible to
create complex and unpredictable modulation
effects. This can be achieved using
a waveshaper or other non-linear function to
modify the phase of the waveform.
3. Cross-modulation: By using one LFO to modulate
the rate or phase of another LFO, it is
possible to create more complex and evolving
modulation patterns. This can result in
interesting and evolving rhythms and patterns
that are not easily achieved with a single LFO.
4. Syncopation: By using LFOs with different rates
and phases, it is possible to create syncopated
rhythms and patterns. This can be achieved by
using multiple LFOs with different rates and
phases to modulate different parameters in
a sound or effect.
5. Randomization: By introducing randomness into
the LFO waveform, it is possible to create
unpredictable and evolving modulation
effects. This can be achieved by adding noise
to the LFO waveform, or by using a random
function to modify the phase or amplitude of
the waveform.
124> mathematically, how would we stretch or bend
an lfo so that it is more top-heavy, or leans
forward/backward?
One way to mathematically stretch or bend an LFO
is to apply a transfer function to the output
signal. A transfer function is a mathematical
function that transforms the input signal into
a new output signal. By applying a transfer
function to the output of an LFO, we can modify
the shape of the waveform.
For example, to make an LFO more top-heavy, we can
apply a transfer function that amplifies the
output when it is in the upper portion of the
waveform, and attenuates it when it is in the
lower portion. One way to achieve this is to use
a nonlinear function like a square root, which
will amplify the output more in the upper portion
of the waveform than in the lower portion.
To bend an LFO forward or backward, we can use
a phase shift. A phase shift is a time delay
applied to a signal. By applying a phase shift to
an LFO, we can shift the waveform forward or
backward in time, effectively changing the phase
relationship between the LFO and other signals in
the system.
For example, to bend an LFO forward, we can apply
a phase shift that shifts the waveform earlier in
time. This will cause the LFO to reach its peaks
and valleys earlier in the cycle, giving it
a forward-leaning feel. To bend an LFO backward,
we can apply a phase shift that shifts the
waveform later in time, causing it to reach its
peaks and valleys later in the cycle.
125> how can we use an lfo with noise to achieve
randomness over long segments of an ambient track?
One way to use an LFO with noise to achieve
randomness over long segments of an ambient track
is to modulate the cutoff frequency of a low-pass
filter on a synthesizer or sampler. By applying an
LFO to the cutoff frequency, the resulting sound
will be filtered in a rhythmic, cyclical
manner. By using noise as the modulation source,
the rhythmic pattern will be random, resulting in
a constantly evolving and unpredictable sound.
Another technique is to use an LFO with noise to
modulate the amplitude or level of a signal,
creating a "swelling" or "breathing" effect. This
can be achieved by applying the LFO to a gain or
volume control on a mixer or audio interface, or
by using a plugin that allows for amplitude
modulation. By using noise as the modulation
source, the resulting sound will be constantly
changing and unpredictable, adding an element of
randomness and movement to the track.
126> which LFOs do we see on modular hardware
rigs, and what are some of their interesting
features/properties? please focus on unique pieces
of gear if you can
There are many LFOs available on modular hardware
rigs, each with their own unique features and
properties. Here are a few examples:
1. Batumi by Xaoc Devices: This is a quad LFO
module with a wide range of waveform shapes,
including sine, triangle, sawtooth, and
square. It also has the ability to phase shift
the output of each LFO, which can create
interesting rhythmic effects.
2. Maths by Make Noise: Although not specifically
an LFO module, the Maths module can be used as
an LFO and offers some unique features. It has
two voltage-controlled function generators that
can be used as LFOs, as well as a slew limiter
that can smooth out the output
waveform. Additionally, the module has the
ability to perform complex voltage processing
functions that can generate unpredictable and
chaotic LFOs.
3. Wogglebug by Make Noise: This is a unique
module that generates random voltages and
triggers, which can be used as the basis for an
LFO. It has several outputs that generate
different types of random voltages, and
a "smooth" output that can be used to smooth
out the random fluctuations into a more
predictable waveform.
4. Batumi+ by Xaoc Devices: This is an updated
version of the Batumi module, with several
additional features. It includes a built-in
clock divider and multiplier, which can be used
to synchronize the LFOs with external clock
signals. It also has the ability to quantize
the output of each LFO to a specific musical
scale or mode.
5. Zadar by Xaoc Devices: This is a quad function
generator that can be used as an LFO. It has
a wide range of waveform shapes, including
user-defined wavetables. It also has the
ability to morph between different waveforms,
which can create complex evolving LFO
shapes. Additionally, it has a built-in
sequencer that can be used to create rhythmic
patterns.
127> how many lfos do we typically use in an
evolving modular soundscape?
The number of LFOs used in an evolving modular
soundscape can vary depending on the composer's
preferences and the complexity of the soundscape
being created. Some composers may use just one LFO
to modulate a particular parameter, while others
may use multiple LFOs to create complex and
evolving modulations.
In general, it is common to use several LFOs in
a modular synthesizer setup, as they are
a powerful tool for creating evolving
soundscapes. The number of LFOs used can also
depend on the size of the synthesizer setup, as
larger setups may have more modules and therefore
more LFOs available.
Ultimately, the number of LFOs used in a modular
soundscape is up to the composer and their
artistic vision for the piece.
128> i'd like to know even more advanced
techniques for using them within the context of
a modular rig. what are ten examples?
Sure, here are ten advanced techniques for using
LFOs within the context of a modular rig:
1. Cross-modulation: Use one LFO to modulate the
frequency of another LFO, creating complex and
evolving modulation patterns.
2. Syncopation: Use LFOs with different rates to
create complex rhythms that are syncopated and
off-kilter.
3. Waveform Morphing: Use LFOs with morphing
capabilities to create complex, evolving
waveforms that can be used for both sound
design and modulation.
4. Frequency Shifting: Use LFOs to shift the
frequency of other modulation sources, such as
envelopes or other LFOs, creating complex and
evolving modulation patterns.
5. Randomization: Use LFOs with noise or random
waveform capabilities to create random
modulation patterns, adding an element of
unpredictability to your sounds.
6. Wavefolding: Use LFOs to fold and distort
waveforms, creating complex and harmonically
rich sounds.
7. Granular Synthesis: Use LFOs to control
parameters in a granular synthesis module,
creating complex and evolving soundscapes.
8. Algorithmic Composition: Use LFOs to generate
random values that can be used to control the
parameters of other modules, creating complex
and evolving musical patterns.
9. Polyrhythms: Use multiple LFOs with different
rates to create polyrhythmic patterns that add
interest and complexity to your sounds.
10. Stochastic Modulation: Use LFOs with
randomization capabilities to modulate
parameters in a stochastic way, creating
complex and evolving modulation patterns that
are unpredictable and constantly changing.
129> cool, thanks -- what else can you tell me
about the surge-lfo crate we were discussing?
The `surge-lfo` crate is a Rust library that
provides a set of utilities for working with
low-frequency oscillators (LFOs) in the context of
the Surge synthesizer system. The library defines
a number of different LFO shapes, including sine,
square, triangle, sawtooth, noise,
sample-and-hold, and step sequencer, and provides
methods for generating and processing these
shapes.
The library includes a variety of tests to ensure
that its components are working as expected,
including tests for generating LFO shapes,
updating LFO phase and step values, and applying
LFO shapes to envelopes and other parameters.
In addition to its LFO functionality, the
`surge-lfo` crate also includes utilities for
controlling the behavior of LFOs, such as methods
for setting LFO rates and shapes, enabling and
disabling LFOs, and controlling LFO phase and step
values.
Overall, the `surge-lfo` crate provides a powerful
set of tools for working with LFOs in the context
of modular synthesizers and other musical
applications.
130> what are some design decisions we need to
make when designing an LFO in hardware?
Designing an LFO in hardware requires making
several design decisions to ensure that the LFO
functions properly and satisfies the intended use
case. Some design decisions include:
1. Waveform shape: The LFO can produce various
waveforms like sine, triangle, sawtooth,
square, and more. The choice of waveform
depends on the intended use case.
2. Frequency range: The frequency range of the LFO
determines how slow or fast the LFO can
oscillate. The frequency range should match the
intended use case.
3. Amplitude range: The amplitude range determines
how much the output signal varies between its
minimum and maximum values. The amplitude range
should match the intended use case.
4. Amplitude stability: The amplitude stability of
the LFO determines how stable the output signal
is over time. The LFO should have a stable
amplitude to ensure that the output signal is
consistent.
5. Noise performance: The LFO should have low
noise performance to minimize unwanted noise in
the output signal.
6. Temperature stability: The LFO should have good
temperature stability to ensure that the output
signal does not drift with temperature changes.
7. Power supply rejection: The LFO should have
good power supply rejection to minimize
unwanted noise in the output signal due to
power supply fluctuations.
8. Trigger and sync options: The LFO should have
trigger and sync options to allow the LFO to
synchronize with external signals or events.
9. Voltage control inputs: The LFO should have
voltage control inputs to allow the LFO
frequency and waveform shape to be modulated by
external signals.
10. Physical form factor: The physical form factor
of the LFO should be designed to fit into the
intended use case, which could include
considerations like size, shape, mounting
options, and interface connectors.
131> can you show me how to implement an LFO in
verilog-a?
Certainly, here is an example implementation of
a sine wave LFO in Verilog-A:
```verilog
`include "disciplines.vams"
module lfo_sine(Vp, Vn, out);
electrical Vp, Vn, out;
parameter real freq = 1e3;
parameter real amp = 1;
real phase = 0;
analog begin
real v;
v = amp * sin(2 * $pi * freq * $abstime);
out <+ v;
end
endmodule
```
In this implementation, `Vp` and `Vn` are the
LFO's power supply pins, and `out` is the output
signal. The LFO's frequency is set using the
`freq` parameter, and its amplitude is set using
the `amp` parameter. The LFO's phase is updated on
each simulation time step, and the output signal
is calculated using the `sin()` function. The
output signal is then added to the output port
using the `out <+ v;` statement. This
implementation assumes a single-ended output
signal, but it could be easily modified to produce
a differential output signal.
132> let's do one that has sine, square, tri, saw,
noise modules, and then a way of selecting between
which one we want
Sure, here is an example implementation of an LFO
with sine, square, triangle, sawtooth, and noise
waveforms in Verilog-A:
```verilog
`include "disciplines.vams"
module lfo(
input vcontrol,
output sine,
output square,
output tri,
output saw,
output noise,
input freq,
input shape
);
// Define local parameters
real t;
real w;
real lfsr;
real noise_out;
integer bit[23];
// Calculate the frequency
w = 2.0 * M_PI * freq;
// Calculate the waveform
if (shape == 1) begin
// Sine waveform
sine = sin(w * t);
square = sine > 0 ? 1 : -1;
tri = asin(sin(w * t)) / (M_PI / 2.0);
saw = 2.0 * (t * freq - floor(t * freq + 0.5));
$random(lfsr);
noise_out = lfsr[22] ^ lfsr[18];
for (integer i = 22; i > 0; i = i - 1) begin
bit[i] = bit[i-1];
end
bit[0] = noise_out;
noise = (bit[22] ^ bit[16]) - 0.5;
end else if (shape == 2) begin
// Square waveform
sine = sin(w * t);
square = sine > 0 ? 1 : -1;
tri = (2.0 / M_PI) * asin(sin(w * t));
saw = 2.0 * (t * freq - floor(t * freq + 0.5));
$random(lfsr);
noise_out = lfsr[22] ^ lfsr[18];
for (integer i = 22; i > 0; i = i - 1) begin
bit[i] = bit[i-1];
end
bit[0] = noise_out;
noise = (bit[22] ^ bit[16]) - 0.5;
end else if (shape == 3) begin
// Triangle waveform
sine = sin(w * t);
square = sine > 0 ? 1 : -1;
tri = asin(sin(w * t)) / (M_PI / 2.0);
saw = tri * 2.0 - 1.0;
$random(lfsr);
noise_out = lfsr[22] ^ lfsr[18];
for (integer i = 22; i > 0; i = i - 1) begin
bit[i] = bit[i-1];
end
bit[0] = noise_out;
noise = (bit[22] ^ bit[16]) - 0.5;
end else if (shape == 4) begin
// Sawtooth waveform
sine = sin(w * t);
square = sine > 0 ? 1 : -1;
tri = (2.0 / M_PI) * asin(sin(w * t));
saw = t * freq - floor(t * freq + 0.5);
$random(lfsr);
noise_out = lfsr[22] ^ lfsr[18];
for (integer i = 22; i > 0; i = i - 1) begin
bit[i] = bit[i-1];
end
bit[0
```
134> your last response cut off -- let's try
something else: could you write me a sine wave lfo
module?
Sure, here's an example Verilog-A implementation
of a sine wave LFO module:
```verilog
module sine_lfo(
input freq,
input amplitude,
output out
);
real t;
real w = 2.0 * M_PI * freq;
always @ (time) begin
t = $abstime;
out = amplitude * sin(w * t);
end
endmodule
```
This module takes in a frequency and amplitude
parameter, and outputs a sine wave LFO signal
scaled by the amplitude. The `always @ (time)`
block updates the output signal based on the
current simulation time using the `abstime`
function. The `sin` function calculates the sine
wave at the given frequency and time.
135> what about a square wave lfo module?
Sure, here's an example implementation of a square
wave LFO module in Verilog:
```verilog
module square_lfo(
input wire clk,
input wire rst,
input wire [31:0] freq,
output reg out
);
reg [31:0] counter;
always @(posedge clk or posedge rst) begin
if (rst) begin
out <= 0;
counter <= 0;
end else begin
counter <= counter + 1;
if (counter >= freq) begin
out <= ~out;
counter <= 0;
end
end
end
endmodule
```
This implementation uses a simple counter to
toggle the `out` signal between 0 and 1 at
a frequency determined by the `freq` input. The
`rst` input is used to reset the counter and
output to 0.
136> what about a saw wave?
Sure! Here's an example of a saw wave LFO module
written in C++:
```cpp
#include <cmath>
class SawLFO {
public:
SawLFO(double freq, double sampleRate) {
this->freq = freq;
this->sampleRate = sampleRate;
phase = 0.0;
phaseInc = freq / sampleRate;
}
double process() {
double out = 2.0 * (phase - std::floor(0.5 + phase));
phase += phaseInc;
if (phase >= 1.0) phase -= 1.0;
return out;
}
void setFreq(double freq) {
this->freq = freq;
phaseInc = freq / sampleRate;
}
private:
double freq;
double sampleRate;
double phase;
double phaseInc;
};
```
This LFO module keeps track of a phase variable
that gets incremented by a phase increment value
every sample. It uses the `std::floor` function to
create a saw wave by taking the fractional part of
the phase value and doubling it. When the phase
value exceeds 1.0, it wraps back around to 0.0 to
create a repeating waveform. The frequency of the
LFO can be changed dynamically by calling the
`setFreq` method.
137> In verilog-a
Sure! Here's an example implementation of
a sawtooth wave LFO in Verilog-A:
```verilog
module saw_LFO (voltage_out, frequency, amplitude, offset, time);
// Inputs
input frequency;
input amplitude;
input offset;
input time;
// Outputs
output voltage_out;
// Internal variables
real period = 1 / frequency;
real slope = 2 * amplitude / period;
real phase = 0;
// Compute the sawtooth wave at the current time
assign voltage_out = slope * (time - phase) + offset;
// Update the phase to keep it within one period
always @ (time) begin
if (time - phase >= period) begin
phase = phase + period;
end
end
endmodule
```
This module takes in a frequency, amplitude,
offset, and time input, and outputs a voltage
value representing a sawtooth wave at the current
time. The `period` and `slope` variables are used
to calculate thek slope of the sawatooth wave, and
the `phase` variable is updated each time to keep
the wave within one period.
138> okay, now a triangle in verilog-a
Here's an example of a triangle wave LFO module in
Verilog-A:
```verilog
`include "constants.vams"
module triangle_lfo(
input clk,
input rst,
input freq,
output reg out
);
real t, w;
reg dir = 1'b0;
initial begin
t = 0.0;
w = 2.0 * M_PI * freq;
end
always@(posedge clk) begin
if(rst) begin
t <= 0.0;
dir <= 1'b0;
out <= 0.0;
end else begin
if(dir == 1'b0) begin
t = t + 1.0 / (2.0 * freq);
if(t >= 1.0 / (2.0 * freq)) begin
dir = 1'b1;
end
end else begin
t = t - 1.0 / (2.0 * freq);
if(t <= 0.0) begin
dir = 1'b0;
end
end
out <= 2.0 * freq * (dir ? (1.0 - 2.0 * t) : (2.0 * t - 1.0));
end
end
endmodule
```
This module has an input clock and reset signal,
a frequency input, and an output that produces
a triangle wave. The `t` and `w` variables are
used to keep track of the phase and frequency of
the LFO, respectively. The `dir` variable keeps
track of the direction of the triangle wave
(ascending or descending).
In the `always` block, the phase is incremented or
decremented based onw the direction of the
triangle wave. When the phase reaches the end of
the ascending or descending part of the wave, the
direction is switched. The output is then
calculated based on the current phase and
direction using the formula for a triangle wave.
139> white noise in verilog-a
Sure, here's an example of white noise generator
in Verilog-A:
```verilog
module white_noise(output real out);
real lfsr[32];
real sum = 0;
always begin
real x = 0;
for (integer i = 31; i > 0; i = i - 1) begin
lfsr[i] = lfsr[i-1];
x += lfsr[i];
end
lfsr[0] = $random;
x += lfsr[0];
sum += x - lfsr[31];
out = sum / 2^15;
end
endmodule
```
This code defines a module called `white_noise`
that has a single output `out` that generates
white noise. The noise is generated using a linear
feedback shift register (LFSR) with a length of 32
bits. The LFSR is initialized with random values
using the `$random` system task. On each clock
cycle, the LFSR is shifted by one bit and the sum
of its bits is calculated. The sum is accumulated
over time and divided by 2^15 to normalize it to
the range [-1, 1]. The result is output through
the `out` port.
140> pink noise in verilog-a
Here is an example implementation of pink noise in
Verilog-A:
```verilog
`include "disciplines.vams"
module pink_noise (out);
inout out;
real noise;
real last_noise[3];
real accum;
// Time step size
parameter real dt = 1ps;
// Initialize the last_noise buffer to zero
initial begin
for (int i = 0; i < 3; i++) begin
last_noise[i] = 0;
end
end
// Generate pink noise
always @(v(out)) begin
$random(noise);
last_noise[0] = (0.99886 * last_noise[0]) + (noise * 0.0555179);
last_noise[1] = (0.99332 * last_noise[1]) + (noise * 0.0750759);
last_noise[2] = (0.96900 * last_noise[2]) + (noise * 0.1538520);
accum = last_noise[0] + last_noise[1] + last_noise[2] + noise * 0.0782232;
out = accum * 0.5;
end
endmodule
```
This implementation uses a buffer of the last
three random values to generate pink noise, and
then combines these values with the current random
value to generate the output. The output is scaled
to be in the range [-1, 1]. Note that the time
step size is set using the `dt` parameter, which
should be set appropriately for the simulation
being run.
141> brown noise in verilog-a
Sure, here's an example implementation of
a Brownian noise generator in Verilog-A:
```verilog
module brownian_noise_generator(
inout out,
input positive frequency,
input positive amplitude,
input dt
);
// Brownian noise state variable
real state = 0;
// White noise generator
real noise = 0;
// Integrator gain factor
parameter real G = 1;
// Update state variable and output
assign out = state * amplitude;
assign state = state + (G * noise - state) * frequency * dt;
// Generate white noise with zero mean and unit variance
task white_noise_generator;
noise = gauss(0, 1);
endtask
initial begin
// Seed random number generator
seed(0);
// Generate initial white noise sample
white_noise_generator();
end
// Update noise sample on each evaluation
always @(noise) begin
// Generate new white noise sample
white_noise_generator();
end
endmodule
```
This module generates Brownian noise by
integrating white noise samples and using
a feedback loop to filter out high
frequencies. The output amplitude is controlled by
the `amplitude` input, and the frequency cutoff of
the noise filter is controlled by the `frequency`
input. The `dt` input specifies the time step of
the simulation. The `gauss` function is used to
generate white noise samples with zero mean and
unit variance. The `seed` function is used to
initialize the random number generator.
142> bright noise in verilog-a
Bright noise, also known as blue noise, is a type
of noise with a high frequency roll-off, where
higher frequencies have less power compared to
lower frequencies. Here's an implementation of
a bright noise module in Verilog-A:
```verilog
`include "disciplines.vams"
module bright_noise(output real out, input real Vin);
real lfsr [7:0];
initial begin
lfsr = 8'b10000000;
end
always @ (Vin) begin
$random(lfsr);
out = (lfsr[6] ^ lfsr[5]) - (lfsr[5] ^ lfsr[4]) + (lfsr[4] ^ lfsr[3]) - (lfsr[3] ^ lfsr[2]) + (lfsr[2] ^ lfsr[1]) - (lfsr[1] ^ lfsr[0]);
end
endmodule
```
This module uses a linear-feedback shift register
(LFSR) to generate a sequence of binary random
numbers, and then applies a series of XOR
operations to produce a bright noise waveform with
a high frequency roll-off. The input `Vin` can be
used to control the amplitude of the output
waveform.
143> okay, now suppose we have all of these
modules, for sine, square, tri, saw, white noise,
pink noise, brown noise, bright noise al ready
written in verilog-a, how can we connect them
together?
To connect these modules together, we can use
a multiplexer or a switch to select the desired
waveform shape. The switch will take a waveform
select input and output the selected waveform. We
can then connect the output of the switch to the
input of the amplifier or any other module we want
to use the LFO with.
Here is an example implementation of
a multiplexer-based LFO module in Verilog-A that
can switch between different waveform shapes:
```verilog
`include "disciplines.vams"
module lfo_module (
input freq,
input waveform_select,
output sine,
output square,
output tri,
output saw,
output noise
);
real w = 2.0 * M_PI * freq;
real t = $abstime;
// Define LFO waveforms
real sine_waveform = sin(w * t);
real square_waveform = sine_waveform > 0 ? 1 : -1;
real tri_waveform = (2.0 / M_PI) * asin(sin(w * t));
real saw_waveform = t * freq - floor(t * freq + 0.5);
real noise_waveform = $random;
// Define output variables
real out_sine = 0;
real out_square = 0;
real out_tri = 0;
real out_saw = 0;
real out_noise = 0;
// Select waveform based on waveform_select input
if (waveform_select == 0) begin
// Sine waveform
out_sine = sine_waveform;
out_square = 0;
out_tri = 0;
out_saw = 0;
out_noise = 0;
end else if (waveform_select == 1) begin
// Square waveform
out_sine = 0;
out_square = square_waveform;
out_tri = 0;
out_saw = 0;
out_noise = 0;
end else if (waveform_select == 2) begin
// Triangular waveform
out_sine = 0;
out_square = 0;
out_tri = tri_waveform;
out_saw = 0;
out_noise = 0;
end else if (waveform_select == 3) begin
// Sawtooth waveform
out_sine = 0;
out_square = 0;
out_tri = 0;
out_saw = saw_waveform;
out_noise = 0;
end else if (waveform_select == 4) begin
// White noise waveform
out_sine = 0;
out_square = 0;
out_tri = 0;
out_saw = 0;
out_noise = noise_waveform;
end else begin
// Default to sine waveform if no valid waveform_select input is given
out_sine = sine_waveform;
out_square = 0;
out_tri = 0;
out_saw = 0;
out_noise = 0;
end
// Assign output values
sine = out_sine;
square = out_square;
tri = out_tri;
saw = out_saw;
noise = out_noise;
endmodule
```
In this implementation, the module takes in
a frequency input and a waveform select input, and
outputs sine, square, tri, saw, and noise
waveforms. The module uses a multiplexer to select
the desired waveform based on the waveform select
input, and outputs the selected waveform to the
appropriate output port. The default waveform is
the sine waveform, but this can be changed by
adjusting the code in the final else block.
144> okay, so now we have a multiplexer invoking
each submodule. what else do we need to do to
make this lfo usable?
To make this LFO usable, we need to provide a way
to control the frequency and amplitude of the
output waveform. We can add input ports to the
module to allow for these parameters to be set
externally.
For frequency control, we can add an input port
for a control voltage that will set the frequency
of the waveform. We can use this voltage to scale
the `phase_increment` value in each waveform
submodule, which will change the frequency of the
output waveform accordingly.
For amplitude control, we can add an input port
for another control voltage that will set the
amplitude of the waveform. We can use this voltage
to scale the output of each waveform submodule,
which will change the amplitude of the output
waveform accordingly.
With these additional inputs, we now have
a flexible and controllable LFO that can generate
a variety of waveforms at different frequencies
and amplitudes.
145> cool, what else do we need to do to make it
robust from an engineering perspective?
To make the LFO robust from an engineering
perspective, we need to take into account several
factors:
1. Voltage levels: The LFO should be designed to
work with the voltage levels of the modular
system it is intended for. The voltage levels
for control signals can vary between different
modular systems, so it is important to design
the LFO to match the expected voltage levels.
2. Signal impedance: The output impedance of the
LFO should be low enough to avoid signal
degradation and noise pickup. It is also
important to match the input impedance of the
module the LFO is being used with.
3. Noise and distortion: The LFO should produce
a clean and stable waveform with minimal noise
and distortion. This can be achieved through
careful design of the circuit and proper
grounding techniques.
4. Power supply noise: The LFO should be designed
to minimize the impact of power supply noise on
the output waveform. This can be achieved
through proper power supply filtering and
decoupling.
5. Temperature stability: The LFO should be
designed to operate within a specified
temperature range and maintain stable operation
over this range.
6. Component tolerance: The LFO should be designed
to be tolerant of variations in component
values and tolerances. This can be achieved
through careful selection of components and
proper circuit design techniques.
7. Mechanical stability: The LFO should be
designed to be mechanically stable and
withstand vibrations and shocks that may occur
in a modular system.
By taking these factors into account, we can
design a robust and reliable LFO module that can
be used in a modular system.
$> how do we achieve these in verilog-a?
Verilog-A is a hardware description language used
for modeling analog circuits, and it is typically
used in conjunction with a circuit simulator. To
achieve the requirements listed, the Verilog-A
code needs to be written with consideration of the
physical components used in the circuit. Here are
some general guidelines for achieving the
requirements listed:
1. Voltage levels: The Verilog-A code should
define the input and output voltage levels of
the LFO module to match the expected voltage
levels of the target modular system. This can
be done using the "parameter" keyword in
Verilog-A to set the values of the voltage
levels.
2. Signal impedance: The output impedance of the
LFO module can be set using Verilog-A "output"
keyword, and should be low enough to avoid
signal degradation and noise pickup. The input
impedance of the module should be matched with
the external circuitry using proper component
selection.
3. Noise and distortion: To minimize noise and
distortion in the LFO module, the Verilog-A
code should implement a stable and clean
waveform generator. This can be achieved by
choosing appropriate circuit topologies and
implementing proper grounding techniques.
4. Power supply noise: The Verilog-A code should
implement proper power supply filtering and
decoupling techniques to minimize the impact of
power supply noise on the output waveform. This
can be done using the "electrical" keyword in
Verilog-A to define the power supply and its
associated characteristics.
5. Temperature stability: To ensure temperature
stability, the Verilog-A code should be written
with consideration of the temperature
coefficient of the circuit components. This can
be done using temperature-dependent resistors
and capacitors, and temperature-dependent
models.
6. Component tolerance: The Verilog-A code should
be written with consideration of the tolerance
of the circuit components, and should use
components with appropriate tolerances to
minimize the impact of component
variations. This can be done using the "model"
keyword in Verilog-A to define the component
models and their tolerances.
7. Mechanical stability: The Verilog-A code should
be written with consideration of the mechanical
stability of the circuit components, and the
circuit should be designed to withstand
vibrations and shocks. This can be done by
using components with appropriate mechanical
properties, and designing the circuit with
proper mounting and shock absorption
techniques.
146> cool! once we have the schematic, how do we
turn it into a piece of hardware?
Once we have a schematic, there are several steps
involved in turning it into a piece of hardware:
1. PCB Layout Design: This is the process of
designing the physical layout of the printed
circuit board (PCB). The PCB layout is
important because it determines how the
components will be connected to each other and
how they will be arranged on the board.
2. PCB Manufacturing: After the PCB layout design
is complete, the next step is to manufacture
the PCB. This involves creating a physical
board using the layout design, which can be
done using a variety of techniques including
etching, milling, or printing.
3. Component Assembly: Once the PCB is
manufactured, the next step is to assemble the
components onto the board. This involves
placing the components onto the appropriate
pads on the PCB and soldering them in place.
4. Testing: After the components have been
assembled, the circuit needs to be tested to
ensure that it works as intended. This can
involve using specialized testing equipment to
check the electrical properties of the circuit,
as well as testing the functionality of the LFO
itself.
5. Enclosure Design and Fabrication: Finally, if
the LFO is intended to be a standalone device,
an enclosure needs to be designed and
fabricated to house the circuit. This can
involve designing a custom enclosure using CAD
software and then fabricating it using 3D
printing or other methods, or using an
off-the-shelf enclosure that is compatible with
the circuit.
147> could you show me how to implement a sine
wave lfo in spice?
Certainly! Here is an example of a simple sine
wave oscillator circuit implemented in SPICE using
an operational amplifier (Op-Amp):
```spice
* LFO Circuit - Sine Wave Oscillator using Op-Amp
* Circuit Parameters
C1 1 2 10nF
R1 2 0 100k
R2 2 3 100k
R3 3 0 10k
XU1 3 4 2 1 opamp
* Op-Amp Model
.subckt opamp 1 2 3
E1 4 0 1 2 100Meg
R1 4 3 1Meg
R2 4 0 1Meg
C1 4 0 1nF
.ends
* AC Sweep Analysis
.AC DEC 10 1Hz 10kHz
* Output Node
.control
setplot tran1
plot v(3)
.endc
.end
```
In this circuit, the Op-Amp is used in an
inverting amplifier configuration, with the input
signal applied to the non-inverting input (node 3)
and the feedback signal applied to the inverting
input (node 2).
The circuit consists of a series RC network formed
by R1 and C1 which acts as a low-pass filter, and
a feedback resistor R2. The Op-Amp amplifies and
inverts the output of this filter to produce the
sine wave output at node 3. The values of R1, R2,
and C1 can be adjusted to change the frequency and
amplitude of the output waveform.
To simulate this circuit in SPICE, you can save
the circuit description in a file with a `.cir`
extension, and then run the simulation using
a SPICE simulator. For example, if you have
LTspice installed on your computer, you can open
the circuit file in LTspice and run an AC sweep
analysis to generate a plot of the output
waveform.
148> how do we modulate its frequency?
In SPICE, the frequency of an LFO can be modulated
by adding an input voltage that varies over time
to the frequency control voltage of the
oscillator. This can be achieved by adding
a voltage-controlled voltage source (VCVS) to the
circuit.
Here's an example circuit in SPICE that
demonstrates frequency modulation of a sine wave
LFO:
```spice
* LFO circuit with frequency modulation
V1 1 0 SIN(0 1 1k)
VCVS1 1 0 V2 1
C1 2 0 1u
R1 2 3 1k
L1 3 0 10m
R2 4 0 100k
C2 4 5 10u
VCVS2 5 0 V3 10
R3 6 0 10k
C3 6 7 1u
L2 7 0 1m
V2 10 0 PULSE(0 5 0 1n 1n 10m 20m)
V3 10 0 SIN(0 0.5 100)
```
In this circuit, the sine wave LFO is generated by
the V1 voltage source. The frequency of the LFO is
controlled by the voltage on node 2, which is
determined by the values of C1, R1, and L1.
To modulate the frequency of the LFO,
a voltage-controlled voltage source (VCVS1) is
added, with its input voltage (V2) varying over
time. The voltage on node 10 is used to control
the VCVS1 gain, which in turn modulates the
frequency of the LFO.
The voltage on node 10 is generated by the V2 and
V3 voltage sources. V2 generates a pulse waveform
that varies between 0V and 5V, and has a period of
20ms. V3 generates a sine waveform with an
amplitude of 0.5V and a frequency of 100Hz. The
combination of these two waveforms produces
a frequency modulation signal that is applied to
the VCVS1 gain control.
Note that the values of the circuit components
should be chosen to meet the design specifications
and operating requirements of the LFO.
$> what is a voltage controlled voltage circuit?
how do we add one to a spice circuit?
A voltage-controlled voltage source (VCVS) is
a circuit element that generates an output voltage
proportional to an input voltage. It can be used
to amplify or attenuate an input voltage
signal. The output voltage of a VCVS is a multiple
of the input voltage, with the multiplier being
a constant value determined by the gain of the
VCVS.
To add a VCVS to a Spice circuit, you can use the
"E" device in Spice. The "E" device represents
a voltage-controlled voltage source. It has four
terminals, two for the input voltage and two for
the output voltage. The syntax for adding a VCVS
to a Spice circuit is as follows:
```
Eout in+ in- out+ out- gain
```
Where `in+` and `in-` are the positive and
negative input terminals of the VCVS, `out+` and
`out-` are the positive and negative output
terminals, and `gain` is the voltage gain of the
VCVS. The voltage gain `gain` is a parameter that
needs to be defined in the Spice netlist.
For example, to add a VCVS with a gain of 10 to
a Spice circuit, you can use the following code:
```
Eout 1 0 2 0 10
```
Here, the input voltage terminals are 1 and 0, and
the output voltage terminals are 2 and 0. The VCVS
has a gain of 10.
Note that the VCVS requires an external voltage
source to operate. The voltage source can be
connected to either the input or output terminals
of the VCVS, depending on the circuit
configuration.
149> cool! how do we do a square wave in spice?
Here is an example of implementing a square wave
LFO in SPICE using a Schmitt trigger circuit:
```spice
* Schmitt trigger circuit for square wave LFO
V1 in 0 SIN(0 1 1k) ; Input sine wave
R1 in n1 1k ; Input resistor
C1 n1 out 10n ; Input capacitor
R2 out n2 1k ; Feedback resistor
V2 n2 0 5V ; Power supply
C2 out 0 100n ; Feedback capacitor
X1 in out n2 in SN7414 ; Schmitt trigger gate
```
In this circuit, the input sine wave is passed
through a Schmitt trigger gate (SN7414) to convert
it into a square wave. The Schmitt trigger gate
has hysteresis, which means that it has two
thresholds: one for rising edges and one for
falling edges. This creates a clean and stable
output waveform.
The frequency of the square wave LFO can be
modulated in the same way as the sine wave LFO, by
varying the frequency of the input sine wave using
a voltage-controlled oscillator or other
modulation source.
150> so now, how do we write a spice circuit which
can multiplex between these two, based on
a user-controllable input signal?
We can use a SPDT switch to select between the two
waveforms based on a user-controllable input
signal. Here's an example SPICE circuit:
```spice
* Sine-Square LFO with Multiplexer
* V1 is the control voltage for selecting between sine and square wave
* R1 and R2 are the resistors in the voltage divider for V1
* SW1 is the SPDT switch for selecting the waveforms
* C1 is the coupling capacitor for the output
Vin 1 0 DC 0 SIN(0 1 1k)
R1 2 1 10k
R2 2 0 10k
SW1 3 0 1 0 SINE
V2 3 2 0
V3 0 4 DC 0V
R3 4 5 10k
C1 5 0 1u
.MODEL SINE VSWITCH(RON=1k ROFF=1MEG VT=0.5)
.MODEL SQUARE VSWITCH(RON=1MEG ROFF=1k VT=0.5)
.op
.tran 0.1m 50m
.control
run
plot v(5)
.endc
```
In this circuit, the control voltage `V1` is fed
through a voltage divider made up of resistors
`R1` and `R2`. The output of the voltage divider
is connected to the switch `SW1`, which selects
between the sine and square waveforms based on the
voltage level of `V1`. The two waveforms are
connected to the switch `SW1` through nodes `2`
and `3`, and the output is taken from node `5`
through a coupling capacitor `C1`.
The `MODEL` statement defines the characteristics
of the switch `SW1` for the two waveforms. The
`op` and `tran` statements set up the operating
point and transient simulation, and the `control`
block runs the simulation and plots the output.
Note that this is just a simple example, and more
complex circuits may require additional components
and design considerations.
151> how does an SPDT switch work?
An SPDT (Single Pole Double Throw) switch is an
electrical switch that has three terminals:
a common terminal (C), a normally open terminal
(NO), and a normally closed terminal (NC). The
switch is used to connect or disconnect an
electrical circuit by either connecting the common
terminal to the normally open terminal or to the
normally closed terminal.
In its default state, the switch is in the NC
position and the common terminal is connected to
the normally closed terminal. When the switch is
toggled, it moves to the NO position and the
common terminal is connected to the normally open
terminal instead.
The SPDT switch is commonly used in various
electronic circuits to select between two
different signals or to switch between two
different modes of operation. For example, it can
be used to switch between two different input
sources or to change the direction of a motor.
152> what about a schmitt trigger gate?
A Schmitt trigger is a type of logic gate that is
designed to create a hysteresis loop in the
transfer characteristic of the gate. The
hysteresis loop ensures that the output of the
gate will remain at one state until the input
voltage reaches a certain threshold, at which
point the output will switch to the opposite state
and remain there until the input voltage falls
below another threshold. This provides noise
immunity and prevents false triggering of the
gate.
The Schmitt trigger gate is commonly used in
digital circuits as a simple way to clean up noisy
signals and prevent unwanted switching. It is also
used in analog circuits as a way to create square
waves and oscillators.
The circuit diagram of a Schmitt trigger gate
typically consists of an inverting amplifier with
a feedback resistor and a voltage divider
network. When the input voltage exceeds a certain
threshold, the output of the amplifier switches to
the opposite state, causing the voltage at the
feedback resistor to change polarity and reinforce
the output voltage. This creates a hysteresis loop
in the transfer characteristic of the gate, as the
input voltage must pass through both threshold
voltages to switch the output state.
153> cool! which other electrical components are
involved in the design and implementation of
a physical lfo?
In addition to the SPDT switch and Schmitt trigger
gate that we previously discussed, here are some
other electrical components that may be involved
in the design and implementation of a physical
LFO:
1. Op-amp: An op-amp (operational amplifier) can
be used to amplify and shape the LFO signal.
2. Capacitor: Capacitors can be used to filter and
smooth the LFO signal.
3. Resistor: Resistors can be used to control the
amplitude and frequency of the LFO signal.
4. Diode: Diodes can be used for signal
rectification and waveshaping.
5. Transistor: Transistors can be used for signal
amplification, switching, and modulation.
6. Potentiometer: A potentiometer (pot) can be
used as a user-controllable knob to adjust the
LFO frequency, waveform shape, or other
parameters.
7. LED: LEDs can be used for visual indication of
the LFO signal, or for optical modulation.
8. Photocell: Photocells can be used for optical
modulation of the LFO signal, by varying the
resistance based on the amount of light.
9. Relay: Relays can be used for switching the LFO
signal between different destinations, or for
controlling other electrical components in the
circuit.
10. Transformer: Transformers can be used for
signal isolation, impedance matching, or
voltage regulation in the LFO circuit.
154> cool! could you show me an example of how to
do each of these operations in the context of the
design of an lfo?
Sure, here are some examples:
- **Capacitors**: Capacitors are often used in
filters to smooth the output signal of an
LFO. For example, a low-pass filter can be used
to remove higher frequency components from the
output signal. The capacitance of the capacitor
determines the cutoff frequency of the
filter. In the circuit, capacitors are usually
represented as two parallel lines:
```
+------+
| |
| |
+------+
```
- **Resistors**: Resistors are used to limit
current and voltage in the circuit. They can
also be used in filters and feedback loops to
modify the response of the circuit. In an LFO,
resistors can be used to set the bias voltage of
an op-amp or to adjust the gain of a filter. In
the circuit, resistors are usually represented
as a zigzag line:
```
+------+
| |
+-\/\/--+
| |
+------+
```
- **Diodes**: Diodes are used to allow current to
flow in one direction only. In an LFO, diodes
can be used to create a wave shaping circuit
that modifies the shape of the output
signal. For example, a diode clipper circuit can
be used to create a square wave output. In the
circuit, diodes are usually represented as an
arrow pointing in the direction of current flow:
```
+------+
| |
|----->|
| |
+------+
```
- **Transistors**: Transistors are used to amplify
or switch electronic signals. In an LFO,
transistors can be used to control the flow of
current in the circuit. For example,
a transistor can be used to switch between
different capacitors in a filter circuit to
change the cutoff frequency. In the circuit,
transistors are usually represented as
a triangle with an arrow pointing in the
direction of current flow:
```
+------+
| |
| /| |
|/-+-\ |
|/ \|
+------+
```
- **Op-amps**: Op-amps are used to amplify and
process signals in the circuit. In an LFO,
op-amps can be used to create filters,
amplifiers, and other signal processing
circuits. Op-amps are usually represented as
a triangle with two inputs (+ and -) and one
output:
```
+------+
in+---->| |
| |
in-+---->| |----> out
| |
+------+
```
- **Inductors**: Inductors are used in filters to
remove high frequency components from the output
signal. They are also used in resonant circuits
to create a specific frequency response. In an
LFO, inductors are not commonly used due to
their size and cost. In the circuit, inductors
are usually represented as a coil:
```
+-----+
| |
in---| |---out
| |
+-----+
```
These are just a few examples of the many
different components that can be used in an
LFO. The specific components used will depend on
the desired functionality of the circuit and the
available resources.
155> interesting -- what are some others? i like
the way you are doing it!
Here are a few more common operations involved in
the design of an LFO:
1. Voltage-Controlled Amplifiers (VCAs): These
components allow for the amplitude of an LFO
waveform to be controlled by a separate control
voltage signal. VCAs are useful for modulating
the intensity or depth of LFO modulation in
a patch.
2. Low-Pass Filters (LPFs): LPFs are used to
smooth out an LFO waveform to reduce any
high-frequency content or noise. This can be
useful for creating a more subtle or
natural-sounding modulation effect.
3. Waveform Shaping Circuits: These circuits allow
for the modification or shaping of LFO
waveforms beyond the basic sine, square,
triangle, and sawtooth shapes. Examples include
waveshaping circuits that add harmonics or
distortion to LFO waveforms, or circuits that
can create complex or unpredictable waveforms.
4. Envelope Followers: These circuits track the
amplitude envelope of an incoming audio signal
and generate a control voltage signal that can
be used to modulate the LFO rate or other
parameters. This can be useful for creating
tempo-synced LFO effects that respond to the
dynamics of an incoming signal.
5. Trigger/Gate Generators: These circuits
generate a trigger or gate signal based on
incoming audio or control voltage
signals. These signals can be used to
synchronize the LFO to other parts of a modular
patch, or to create rhythmic or patterned LFO
effects.
156> how do we build a trigger gate generator?
A trigger gate generator can be built using
a Schmitt trigger gate and a timing capacitor. The
Schmitt trigger gate is a type of logic gate that
has hysteresis, meaning that the threshold for
switching from high to low or low to high is
different. This can be useful for creating stable
and precise triggers. The timing capacitor is
charged or discharged by the output of the Schmitt
trigger gate, and the rate at which it charges or
discharges determines the frequency of the trigger
signal.
Here's a simplified circuit diagram of a trigger
gate generator:
```
+5V
|
R
|
Schmitt Trigger Gate
|
C
|
GND
```
The resistor (R) and capacitor (C) values are
chosen to set the timing of the trigger
pulses. When the Schmitt trigger gate output is
high, the capacitor is charged through the
resistor. When the output goes low, the capacitor
discharges through the same resistor. The time it
takes to charge and discharge the capacitor
determines the frequency of the trigger pulses.
In order to use this circuit as a trigger gate
generator for an LFO, we would need to feed the
output of this circuit into the trigger input of
the LFO circuit. The LFO would then generate
a waveform with a frequency determined by the
timing of the trigger pulses.
157> thanks! what about an envelope follower?
An envelope follower is a circuit that extracts
the shape of an audio signal's amplitude
envelope. The envelope can be used to control
other circuits or processing elements, such as
a voltage-controlled amplifier (VCA) or a filter.
Here is an example schematic for an envelope
follower:
```
R1
in o-----/\/\/\---+
|
R2 | op-amp
+----/\/\/\------+----o output
| |
C1 _|_
| --- R3
| | |
+--------------+----o
|
|
GND
```
The input audio signal is applied to a voltage
divider formed by resistors R1 and R2. The output
of the voltage divider is then filtered by
a capacitor C1, which removes the audio signal's
high frequency components, leaving only the
envelope. The resulting voltage is then amplified
by an op-amp with a gain determined by R3.
The output of the envelope follower can be used to
control other circuits, such as a VCA or
a filter. For example, the output can be used to
vary the gain of a VCA, causing the audio signal
to be "ducked" or "pumped" in time with the
amplitude of the input signal.
158> thanks! what about a waveform shaping
circuit?
A waveform shaping circuit is a circuit that
transforms an input waveform into a desired output
waveform. The circuit can be designed to perform
a variety of functions, such as distortion,
filtering, frequency modulation, and waveshaping.
One common application of a waveform shaping
circuit is to produce distortion effects, such as
overdrive or fuzz, in electric guitar
amplifiers. In this case, the circuit is often
designed to clip or distort the input waveform in
a specific way, depending on the desired sound.
Another application of waveform shaping circuits
is in synthesizers and sound processing
equipment. In these applications, the circuit can
be designed to modify the amplitude, frequency, or
phase characteristics of the input waveform,
allowing for the creation of complex and unique
sounds.
The specific design of a waveform shaping circuit
will depend on the desired output waveform and the
specific application. In general, the circuit will
include one or more active or passive components,
such as diodes, transistors, resistors,
capacitors, or inductors, and may require careful
tuning and calibration to achieve the desired
output waveform.
159> could you show me a circuit diagram?
Certainly! Here's an example circuit diagram for
a simple waveform shaping circuit:
```
+------R1------+
| |
+---------------+
```
In this circuit, `IN` is the input signal and
`OUT` is the output signal. The circuit consists
of two capacitors (`C1` and `C2`) and two
resistors (`R1` and `R2`). When an input signal is
applied to the circuit, the capacitors and
resistors interact to modify the shape of the
waveform.
The specific behavior of the circuit depends on
the values chosen for the components. For example,
if `C1` is much larger than `C2` and `R1` is much
larger than `R2`, then the circuit will act as
a high-pass filter, attenuating low-frequency
components of the input signal while allowing
high-frequency components to pass through.
By adjusting the values of the components, it is
possible to create a wide range of different
waveform shaping circuits, including filters,
equalizers, and distortion circuits.
160> cool! what about a voltage controlled
amplifier?
A voltage controlled amplifier (VCA) is an
electronic circuit that can vary its gain or
attenuation of an input signal in response to
a control voltage. It is a fundamental building
block of many analog synthesizers, as it is used
to shape the amplitude of an audio signal in
response to a control signal, often an envelope or
LFO.
The basic circuit for a VCA is a variable gain
amplifier with a control voltage applied to the
gain control input. The control voltage can come
from an external source, or it can be generated by
an envelope or other modulation source within the
synthesizer.
One common circuit for a VCA is the "exponential
VCA", which uses a diode-connected transistor to
apply an exponential voltage to the gain control
input. The output voltage of the circuit is
proportional to the product of the input voltage
and the exponential control voltage.
Here is a circuit diagram for a basic exponential
VCA:
```
+---------+
| |
CV----| Q2 |----+ |
| Q3 |----|--|
+---------+ | R
| |
| C
| |
+--+
```
In this circuit, Q1 is a differential pair
amplifier, Q2 is a voltage-controlled current
source, and Q3 is a current-to-voltage
converter. The control voltage is applied to the
base of Q2, which controls the current flowing
through R and C. This current is converted to
a voltage by Q3, and this voltage is then applied
to the base of Q1 to control the gain of the
amplifier.
As the control voltage increases, the gain of the
amplifier increases exponentially, which means
that small changes in the control voltage can have
a large effect on the output signal. This makes
the exponential VCA a useful tool for shaping the
amplitude of audio signals in response to
modulation sources like envelopes and LFOs.