Twang

Library for pure Rust advanced audio synthesis.

Goals

• Fast: Auto-vectorized audio synthesis.
• Pure Rust: No system dependencies outside std.

Links to examples for each will be provided as they are implemented.

• Additive synthesis (Compositing sounds, usually sine waves - used in analysis / resynthesis along with FFT)
• Subtractive synthesis (Shaping sawtooth wave, which contains both odd and even frequencies, with filters to boost or reduce frequencies)
• Frequency Modulation synthesis (Modulating frequency with a waveform)
  • Phase Modulation (PM) synthesis - An implementation of FM used in popular 1980s synthesizers
• Phase Distortion synthesis (Inverted Frequency Counter multiplied by sine wave at resonance frequency: A higher frequency counter that starts over / resets at the end of the fundamental frequency)
• Physical modeling synthesis (Karplus-Strong algorithm, other Digital waveguide synthesis using d'Alembert's algorithm)
• Sample-Based / Wavetable Lookup synthesis (Whats used in MIDI)
• Linear arithmetic synthesis (PCM sampled attack + subtractive synthesis sustain)
• Vector synthesis (Mix of four sounds based on an X-Y plane)
• Phase Offset Modulation Synthesis (two instances of a periodic waveform kept slightly out of sync with each other, then are either multiplied or subtracted)
• Arbitrary waveform synthesis (Defined samples occuring at different times in a waveform, called waypoints - either jump or interpolate {video game music})

Waveforms

Oscillators:

• Frequency Counter (Fc / Sawtooth) - odd and even harmonics that decrease at -6 dB/octave
• Pulse Wave (When ½ duty cycle set to 1.0 is a Square Wave - odd harmonics that decrease at -6 dB/octave)
• Sine Wave - no harmonics
• Triangle Wave - odd harmonics that decrease at -12 dB/octave

"Voltage" Controlled filter:

• Lowpass (Most Common) / Highpass
• Bandpass / Notch

Envelope (example: ADSR):

• Press: Attack (time, oscillator:Fc), Hold?, Decay (time, oscillator:Fc.inv), …
• Hold: Sustain (oscillator:Pulse(1.0).Gain(level))
• Release: Release (time, oscillator:Fc.inv)

"Voltage" Controlled amplifier (multiplication)

Effects

Gated Reverb

Reverb without reflections.

Gated Reverb

Reverb And Echo

Reverb is just echo that takes place in less than 50 milliseconds, so you can use the same APIs.

Decibel Normalization

When generating waveforms you may want to normalize by the volume of the wave, which the amplitude doesn't always accurately approximate. First, calculate the RMS (Root Mean Square).

let sum = 0
for sample in samples {
    sum += sample * sample
}
sum /= samples.len()
let rms = sum.sqrt()

Now the peak value:

let mut peak_amplitude = 0
for sample in samples {
    peak_amplitude = peak_amplitude.max(sample.abs())
}

Next the crest factor:

let crest_factor = peak_amplitude / rms

Then decibels:

let papr = 20 * log10(crest_factor)

Crest Factor Post-processed Recording 4–8 / 12–18 dB headroom Crest Factor Unprocessed Recording 8–10 / 18–20 dB headroom

And actual perceived volume should be calculated with ITU-R BS.1770-4

Getting Started

Examples can be found in the Documentation and the examples folder.

MSRV

The minimum supported Rust version of twang is 1.60.0. MSRV may only be updated when increasing the leftmost version number of twang.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE_APACHE_2_0.txt or https://www.apache.org/licenses/LICENSE-2.0)
• Boost License, Version 1.0 (LICENSE_BOOST_1_0.txt or https://www.boost.org/LICENSE_1_0.txt)
• MIT License, (LICENSE_MIT.txt or https://mit-license.org/)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Anyone is more than welcome to contribute! Don't be shy about getting involved, whether with a question, idea, bug report, bug fix, feature request, feature implementation, or other enhancement. Other projects have strict contributing guidelines, but this project accepts any and all formats for pull requests and issues. For ongoing code contributions, if you wish to ensure your code is used, open a draft PR so that I know not to write the same code. If a feature needs to be bumped in importance, I may merge an unfinished draft PR into it's own branch and finish it (after a week's deadline for the person who openned it). Contributors will always be notified in this situation, and given a choice to merge early.