# noise

sample-by-sample digital audio processing in zig.

inspired by [torvalds/AudioNoise](https://github.com/torvalds/AudioNoise).

## philosophy

- single sample in, single sample out
- zero latency (no block processing)
- IIR filters and delay lines only
- no FFT, no complex transforms
- learn by building

## what's here

- **biquad** - second-order IIR filter (lowpass, highpass, bandpass, notch, allpass)
- **lfo** - low frequency oscillator (sine, triangle, sawtooth)
- **wav** - wav file writer (44-byte header + samples, no ffmpeg)

## compositions

### ambient

```bash
zig build ambient   # generates ambient.wav
```

an eno-inspired generative piece. a low C2 drone serves as the constant tonal center, while auxiliary voices (fifth, octave, major third, major seventh) fade in and out on their own long cycles. each voice has a prime-number period (17, 19, 23, 29, 31 seconds) so they never sync up - sometimes you hear just the drone, sometimes several voices bloom together, never the same combination twice.

## usage

```zig
const noise = @import("noise");

// create a lowpass filter at 1kHz
const lpf = noise.biquad.lowpass(1000, 0.707, 48000);
var state: noise.State = .{};

// process samples
for (input_samples) |sample| {
    const output = noise.biquad.step(lpf, &state, sample);
    // ...
}
```

## example

```bash
zig build run   # generates output.wav
```

a 440Hz sine with lowpass filtering and tremolo. demonstrates basic synthesis pipeline.

## install

```zig
// build.zig.zon
.noise = .{ .url = "https://tangled.sh/@zzstoatzz.io/noise/archive/main" },

// build.zig
const noise = b.dependency("noise", .{}).module("noise");
exe.root_module.addImport("noise", noise);
```

## test

```bash
zig build test
```