11 releases
0.2.12alpha.0  Apr 7, 2023 

0.2.11alpha.0  Dec 19, 2022 
0.2.5alpha.0  Jun 21, 2022 
0.2.4alpha.0  Mar 14, 2022 
0.1.42alpha.0  Oct 27, 2021 
#8 in #lowpass
106 downloads per month
Used in surgesynthesizer
495KB
9K
SLoC
surgefilterk35
The surgefilterk35
crate provides a set of
filters based on the K35 algorithm, which is
a variant of the classic Korg 35 filter used in
analog synthesizers. The K35 algorithm provides
a flexible and powerful way to implement lowpass
and highpass filters with adjustable cutoff
frequencies and resonance.
The crate provides two main filter types: LPF
(lowpass filter) and HPF
(highpass filter), each
with its own set of coefficients and processing
functions. The filters can be configured using
a clamped frequency parameter, which determines
the cutoff frequency of the filter as a fraction
of the sampling rate.
The filters are implemented using a cascade of secondorder IIR filters, or biquads, which provide a flexible and efficient way to implement complex frequency response curves. The biquad processing functions use the Direct Form II Transposed structure, which is a canonical way to implement IIR filters in a computationally efficient way.
The coeff_make
function is used to compute the
filter coefficients based on the desired filter
parameters. The function takes as input the filter
type (lowpass or highpass), the sampling rate, the
clamped frequency, and the resonance (Q factor),
and returns a set of filter coefficients in
a FilterCoeffs
struct.
The process_lp
and process_hp
functions are
used to process input signals with the lowpass and
highpass filters, respectively. The functions take
as input the filter coefficients, the input
signal, and a mutable output buffer, and apply the
filter to the input signal in place.
The do_lpf
and do_hpf
functions are
convenience functions that wrap the coeff_make
and process_lp
/process_hp
functions to provide
a simpler API for processing signals with the
lowpass and highpass filters.
The process_quad
function is a lowerlevel
function that implements the biquad processing
logic directly. It takes as input the biquad
coefficients, the input signal, and a mutable
state buffer, and applies the biquad filter to the
input signal in place.
Overall, the surgefilterk35
crate provides
a flexible and efficient way to implement K35
filters in Rust, with a simple and intuitive API
that is wellsuited for realtime audio processing
and other signal processing applications.
11> thanks! could you show me how to implement the korg 35 filter in veriloga?
Sure! Here's an example implementation of the Korg 35 filter in VerilogA:
// veriloga, (using verilog highlighting)
module korg_35_filter (
input real x,
output real y,
parameter real fc = 1000, // cutoff frequency
parameter real q = 0.5 // resonance
);
real fs = $abstime_step(); // sampling rate
real w0 = 2 * $pi * fc / fs; // normalized cutoff frequency
real alpha = sin(w0) / (2 * q); // filter resonance
real a0 = 1 + alpha;
real a1 = 2 * cos(w0);
real a2 = 1  alpha;
real b0 = (1  cos(w0)) / 2;
real b1 = 1  cos(w0);
real b2 = (1  cos(w0)) / 2;
real x1, x2, y1, y2;
initial begin
x1 = 0;
x2 = 0;
y1 = 0;
y2 = 0;
end
analog begin
real v0 = x  a1 * x1  a2 * x2;
real v1 = b0 * v0 + b1 * x1 + b2 * x2;
real v2 = a0 * y1  a1 * y2 + v1;
y = v2;
x2 = x1;
x1 = x;
y2 = y1;
y1 = y;
end
endmodule
This implementation uses the normalized cutoff
frequency w0
and resonance alpha
to compute
the filter coefficients a0
, a1
, a2
, b0
,
b1
, and b2
. The filter is implemented using
a Direct Form II Transposed structure, which is
a common way to implement IIR filters in
VerilogA.
The x1
, x2
, y1
, and y2
variables are used
to store the previous input and output samples for
each stage of the filter, and are updated on each
simulation time step using VerilogA's analog
block.
To use this filter in your VerilogA simulation,
you can instantiate the korg_35_filter
module
and connect its x
and y
ports to your input
and output signals, respectively. You can also
adjust the fc
and q
parameters to configure
the filter cutoff frequency and resonance to meet
your specific requirements.
Note that VerilogA is a behavioral modeling language, and its performance and accuracy may vary depending on the simulation environment and settings. For highperformance or highprecision simulations, you may want to consider using a more specialized hardware description language such as Verilog or VHDL, or a specialized filter design tool such as MATLAB or Python's scipy.signal library.
12> thanks! what are the mathematical properties of this algorithm?
The Korg 35 filter is a type of secondorder Infinite Impulse Response (IIR) filter that is commonly used in analog synthesizers. Here are some of the mathematical properties of the Korg 35 filter algorithm:

Linearity: The Korg 35 filter is a linear system, which means that its input/output relationship is linear. In other words, the output of the filter is a linear combination of its input and previous output samples.

Timeinvariance: The Korg 35 filter is a timeinvariant system, which means that its behavior does not change over time. In other words, the filter's response to an input signal is the same at any point in time.

Memory: The Korg 35 filter is a recursive system, which means that it has memory. The filter output depends not only on the current input sample, but also on past input and output samples.

Frequency response: The frequency response of the Korg 35 filter depends on the location of its poles and zeros in the complex plane. The filter's magnitude and phase response can be analyzed using tools such as the Fourier transform and the Ztransform.

Stability: The stability of the Korg 35 filter depends on the location of its poles in the complex plane. If all of the poles are inside the unit circle, the filter is stable and its output will not grow without bound.

Nonlinear phase: The Korg 35 filter has a nonlinear phase response, which means that it can introduce phase distortion in the filtered signal. This can be a desirable or undesirable effect depending on the application.

Resonance: The Korg 35 filter has a resonance parameter, which controls the peak gain of the filter at its cutoff frequency. This can be used to create a resonant peak or notch in the frequency response of the filter.
These mathematical properties of the Korg 35 filter algorithm are important for understanding its behavior and performance in various applications. By manipulating the location of the poles and zeros, adjusting the resonance parameter, and selecting the appropriate implementation method, you can design Korg 35 filters with a wide range of characteristics to meet your specific requirements.
13> what distinguishes it from other IIR filters?
The Korg 35 filter is a type of Infinite Impulse Response (IIR) filter that is widely used in analog synthesizers. What distinguishes the Korg 35 filter from other IIR filters are its specific design characteristics and resulting frequency response. Here are some of the key features that distinguish the Korg 35 filter from other IIR filters:

Resonance: The Korg 35 filter is known for its strong resonance characteristic, which allows it to create a peak or notch in the frequency response at the cutoff frequency. This makes it wellsuited for use in audio processing applications such as equalizers, tone controls, and other filters that require precise frequency shaping.

Nonlinear phase response: The Korg 35 filter has a nonlinear phase response, which means that it can introduce phase distortion in the filtered signal. This can be a desirable or undesirable effect depending on the application, but it makes the Korg 35 filter wellsuited for use in audio processing applications where the phase response is an important consideration.

Secondorder implementation: The Korg 35 filter is implemented as a cascade of secondorder IIR filters, or biquads. This provides a flexible and efficient way to implement complex frequency response curves, and allows for a greater degree of control over the filter response.

Adjustable cutoff frequency: The Korg 35 filter has an adjustable cutoff frequency, which can be set to any frequency within the passband of the filter. This makes it wellsuited for use in applications where precise control over the frequency response is required.

Analog heritage: The Korg 35 filter was originally designed for use in analog synthesizers, and its implementation reflects this heritage. While it can be implemented digitally, it has a distinct character and warmth that is often associated with analog filters.
Overall, the Korg 35 filter is distinguished from other IIR filters by its strong resonance characteristic, nonlinear phase response, secondorder implementation, adjustable cutoff frequency, and analog heritage. These features make it a popular choice for audio processing applications where precise frequency shaping and a distinct character are desired.
14> thanks  any caveats? what should we keep in mind while using it?
While the Korg 35 filter is a powerful and versatile tool for audio processing and other signal processing applications, there are several caveats and considerations that should be kept in mind when using it:

Resonance can lead to instability: The resonance characteristic of the Korg 35 filter can cause instability if it is set too high. This can result in unpredictable and erratic behavior, and can damage speakers or other audio equipment. It is important to use the resonance control with care, and to ensure that the filter is properly designed and implemented to avoid instability.

Nonlinear phase response can introduce artifacts: The nonlinear phase response of the Korg 35 filter can introduce artifacts in the filtered signal, such as phase distortion or frequencydependent delay. This can be a desirable or undesirable effect depending on the application, but it is important to be aware of the potential for artifacts and to design the filter appropriately to minimize their impact.

Secondorder implementation requires careful design: The Korg 35 filter is implemented as a cascade of secondorder IIR filters, or biquads. While this provides a flexible and efficient way to implement complex frequency response curves, it also requires careful design and tuning to ensure stability and accuracy.

Analog implementation can introduce noise and distortion: While the Korg 35 filter can be implemented digitally, it has an analog heritage and is often associated with analog filters. Analog implementation can introduce noise and distortion, which may be desirable or undesirable depending on the application.

Limitations of digital implementation: Digital implementation of the Korg 35 filter can introduce quantization noise and other artifacts, and can be limited by the available processing power and precision. It is important to design the filter appropriately for the available hardware and software, and to ensure that the implementation meets the desired performance criteria.
Overall, the Korg 35 filter is a powerful and versatile tool that requires careful design and implementation to achieve the desired results. By understanding the potential caveats and limitations, and by designing the filter appropriately, you can take full advantage of the Korg 35 filter's unique characteristics and capabilities in your signal processing applications.
15> what other filters are in its family tree?
The Korg 35 filter is part of a family of filters that are commonly used in analog synthesizers and other audio processing applications. Here are some of the other filters that are related to the Korg 35 filter:

Moog ladder filter: The Moog ladder filter is a classic analog filter design that was used in the original Moog synthesizers. Like the Korg 35 filter, the Moog ladder filter has a strong resonance characteristic and a nonlinear phase response.

Statevariable filter: The statevariable filter is a type of filter that can be configured as a lowpass, highpass, or bandpass filter. It is often used in analog synthesizers, and is known for its flexibility and versatility.

SallenKey filter: The SallenKey filter is a type of active filter that is commonly used in audio processing and other signal processing applications. It is a secondorder filter that can be configured as a lowpass, highpass, or bandpass filter.

Butterworth filter: The Butterworth filter is a type of IIR filter that has a maximally flat frequency response in the passband. It is often used in audio processing and other signal processing applications where a flat frequency response is desired.

Chebyshev filter: The Chebyshev filter is a type of IIR filter that has a steeper rolloff than the Butterworth filter, but has a ripple in the passband. It is often used in audio processing and other signal processing applications where a steeper rolloff is desired.
These filters, along with the Korg 35 filter, are part of a rich heritage of analog filter designs that have been used in a wide range of applications. Each filter has its own unique characteristics and tradeoffs, and the choice of filter depends on the specific requirements of the application.
16> could you please provide 10 examples of projects which may benefit from using this crate?
Sure, here are ten examples of projects that may
benefit from using the surgefilterk35
Rust
crate:

Audio synthesizers: The Korg 35 filter is a common filter used in audio synthesizers, and the
surgefilterk35
crate could be used to implement the filter in software. 
Audio effects processors: The Korg 35 filter can also be used in audio effects processors such as equalizers, tone controls, and other filters. The
surgefilterk35
crate could be used to implement these filters in software. 
Music production software: Music production software such as digital audio workstations (DAWs) and virtual instruments can benefit from the Korg 35 filter's unique resonance and nonlinear phase characteristics. The
surgefilterk35
crate could be used to implement the filter in these applications. 
Audio processing research: Researchers in audio processing may use the
surgefilterk35
crate as a tool for exploring the characteristics of the Korg 35 filter and its variants. 
Audio programming tutorials: The
surgefilterk35
crate could be used in audio programming tutorials as an example of a filter implementation in Rust. 
Analog modeling software: The Korg 35 filter is often used as a reference filter for analog modeling software. The
surgefilterk35
crate could be used to implement the filter in these applications. 
Music visualization software: Music visualization software that reacts to audio signals in realtime could benefit from the Korg 35 filter's unique frequency response and resonance characteristics. The
surgefilterk35
crate could be used to implement the filter in these applications. 
Audio art installations: Audio art installations that require realtime audio processing could benefit from the Korg 35 filter's unique characteristics. The
surgefilterk35
crate could be used to implement the filter in these installations. 
Audio game development: Game developers that require realtime audio processing could use the Korg 35 filter in audio effects such as filters and synthesizers. The
surgefilterk35
crate could be used to implement these effects in game audio. 
Audio hardware design: Audio hardware designers may use the
surgefilterk35
crate as a tool for simulating the behavior of the Korg 35 filter in software before implementing the filter in hardware.
Overall, the surgefilterk35
Rust crate could be
useful in a wide range of audio processing
applications that require realtime processing,
precise frequency shaping, and a distinct
character in the audio output.
17> how could we use this crate in game development?
The surgefilterk35
Rust crate could be used in
game development to implement audio effects such
as filters and synthesizers that require realtime
processing and a unique character in the audio
output. Here are some examples of how this crate
could be used in game development:

Sound design: The Korg 35 filter is known for its strong resonance characteristic, which can be used to create interesting and unique sounds in games. The
surgefilterk35
crate could be used to implement the filter in software and create custom sounds for game assets such as weapons, vehicles, and environments. 
Music production: Games that feature original music compositions could benefit from the Korg 35 filter's unique resonance and nonlinear phase characteristics. The
surgefilterk35
crate could be used to implement the filter in software and process the music in realtime to create interesting and dynamic soundscapes. 
Realtime audio effects: Games that feature realtime audio effects such as filters and synthesizers could use the
surgefilterk35
crate to implement these effects in software. This could be used to create immersive sound environments, dynamic soundtracks, and unique audio effects. 
Sound processing for voiceover: Games that feature voiceover could use the Korg 35 filter to process the voice audio and add interesting effects to the audio output. The
surgefilterk35
crate could be used to implement the filter in software and add effects such as resonance, filtering, and distortion to the voice audio. 
Audiodriven gameplay: Games that use audio cues to drive gameplay mechanics could use the Korg 35 filter to create unique audio feedback for player actions. The
surgefilterk35
crate could be used to implement the filter in software and create audio effects that respond dynamically to player actions in realtime.
Overall, the surgefilterk35
Rust crate could be
a useful tool in game development for creating
unique and interesting audio effects that enhance
the player's experience and add to the overall
immersion of the game.
Dependencies
~12–22MB
~314K SLoC