Dsp Engineering

DSP Engineering

The Audio Thread Contract

On the audio thread, you MUST NOT:

• Allocate/deallocate memory (no new, malloc, Vec::push, Box)
• Lock mutexes (use lock-free alternatives)
• Make system calls (no file I/O, no logging, no printing)
• Throw/catch exceptions (C++)
• Call virtual functions in hot paths (C++)

Cardinal Rules

1. Pre-allocate everything before audio starts
2. Use fixed-size buffers - size known at initialization
3. Smooth parameters - never jump values (causes clicks)
4. Process in blocks - batch operations for cache efficiency
5. Denormals kill performance - flush to zero

Quick Reference

Common Formulas

// Frequency to angular frequency
omega = 2 * PI * freq / sample_rate

// dB to linear gain
gain = 10^(dB / 20)

// Linear gain to dB
dB = 20 * log10(gain)

// MIDI note to frequency
freq = 440 * 2^((note - 69) / 12)

// Smoothing coefficient from time constant
coeff = 1 - exp(-1 / (time_ms * sample_rate / 1000))

Typical Processing Loop

fn process(&mut self, output: &mut [f32]) {
    for sample in output.iter_mut() {
        // 1. Get smoothed parameters
        let freq = self.freq_smoother.next();

        // 2. Generate/process audio
        let osc = self.oscillator.next(freq);

        // 3. Apply effects chain
        let filtered = self.filter.process(osc);

        // 4. Output with gain
        *sample = filtered * self.gain_smoother.next();
    }
}

Denormal Prevention

// Rust: flush denormals
fn flush_denormal(x: f32) -> f32 {
    if x.abs() < 1e-15 { 0.0 } else { x }
}

// Or use a small DC offset in feedback paths
const DC_OFFSET: f32 = 1e-25;

// C++: set FTZ/DAZ flags at plugin init
#include <xmmintrin.h>
_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON);
_MM_SET_DENORMALS_ZERO_MODE(_MM_DENORMALS_ZERO_ON);

Converted and distributed by TomeVault — claim your Tome and manage your conversions.