watch-later/sndfilter

Algorithms for sound filters, like reverb, dynamic range compression, lowpass, highpass, notch, etc

sndfilter

Algorithms for sound filters, like reverb, dynamic range compression, lowpass, highpass, notch, etc.

It's easy to find countless math equations on sound filters, but a bit harder to find simple source code. This library is my attempt at cleaning up and presenting the math-heavy filter algorithms for the programming community.

(MIT License)

Build Instructions

The ./build script is a simple bash script that compiles the source files using clang. It's dirt simple, I promise.

Simply run ./build and the executable should be ./tgt/sndfilter.

Filters

• Reverb (Algorithmic)
• Compressor
• Low-Pass (Cutoff, Resonance)
• High-Pass (Cutoff, Resonance)
• Band-Pass (Frequency, Q)
• Notch/Band-stop (Frequency, Q)
• Peaking (Frequency, Q, Gain)
• All-Pass (Frequency, Q)
• Low Shelf (Frequency, Q, Gain)
• High Shelf (Frequency, Q, Gain)

Implementation

The reverb.c, compressor.c, and biquad.c are the core algorithms.

I do not understand the biquad math, so please don't ask me any questions :-). The core formulas were extracted from Biquad.cpp (Chromium source), and cleaned up a bit to make easier to read.

The compressor came from DynamicsCompressorKernel.cpp (also from Chromium), and cleaned up a bit more. I swapped out the adaptive release curve and simplified the knee calculations. I feel a little more comfortable with that algorithm because there isn't a whole lot of magical math involved.

The reverb effect is a complete rewrite of Freeverb3's Progenitor2 algorithm. It took quite a lot of effort to tear apart the algorithm and rebuild it, but I'm pretty sure it's right.