Sound Tests

Various small test programs that I am creating to learn more about audio processing.

Audio synthesis tests:

1: Hello Sine - Play a sine wave

Creates a sine wave for one second on the default audio device
Can change the frequency
Very similar to the cpal example code

2: Samples - Play various samples

Adds new functionality on to '1: Hello Sine'
Can now create a Sine, Square, Sawtooth or Triangle sound
RunArgs struct -- change the sample in the main fn, change the frequency

RunArgs::generate_arrays

If this boolean set true no sound will play
Instead a text file samples.txt will be generated in the crate root
The python script at tools/plot.py will open this data when run and plot the sample
This lets you inspect and verify if the samples are correct

3: Mix - Combine the various samples

Adds new functionality on to '2: Samples'
Can now mix and play many samples at once
RunArgs struct now takes a Vec of (Sample, Freq) pairs to specify the sounds you want to mix
Added Silence waveform that has no effect when mixing just for testing
Will mix all the sounds and normalize the amplitude of the combined sample
RunArgs::generate_arrays is still supported so you can view the mixed samples using tools/plot.py

RunArgs::generate_arrays extension new functionality

Now also generates a samples.wav file in addition to the samples.txt so you can listen to the audio

Configurable constants

Both of these optimizations are on by default just to make the code run fast. Seems to be fine but I haven't proven the correctness of them to myself so I made them toggleable.

FAST_AMPLITUDE - Take a shortcut guess when calculating amplitude. Much faster and probably good enough
CAP_ARRAY_GENERATION_SIZE - Another shortcut guess when calculating amplitude. Can stop giant sample expansions.

4: FM Synth - Simple FM Synthesis

Modifies '3: Mix' but is not additive, removes the ability to mix
RunArgs changed. Takes a 'carrier' (Wave, Freq) for the base waveform and a list of modulators
Modulators consist of (Wave, Freq, Depth)
The final waveform is frequency modified (by the list of modulators, first to last)
Modulators run in a linear chain progressively modifying each others output
More complex FM synthesis chains/trees are possible but I've just done the simplest thing here
Added a new waveform OnOff that is 1 for half its period than 0 for the rest (useful for modulators?)
RunArgs hide_device_out will disable audio device information prints but not other information.. is overriden by quiet flag
Also normalized the sine wave (can correctly generate sample values after 1sec of playback)

FM Synth example

The following setup sounds like a harsher telephone ringing sound:

carrier: (WaveformKind::Sine, 440.0),
modulators: vec![
    (WaveformKind::Square, 1760.0, 22.0),
],

Tools (python scripts)

plot.py and plot2.py are interchangeable
plot.py uses native desktop rendering
plot2.py uses browser rendering

Tests (as in not sure if they're good)

1: Lowpass

Modify '3: Mix' and add a naive first order low pass filter
Only parameter is a cutoff frequency
Seems to impart noise and phase shift on the output
Needs more research...

2: Play midi input

Modify '3: Mix' adding midi reading
Keep track of currently activated notes and their velocities, mixes them
Scales the linear midi velocities into an exponential to guess/match perceived loudness
Lets you pick your midi device and wave choice
'Unlimited' polyphony
BASIC MIDI SUPPORT INCLUDES: channel 0, Commands: Note on, Note off
I think it has a decent amount of delay from keypress -> note heard.. not sure

Outdated documentation

OLD FM synthesis examples

WARNING: These only apply to an older version (commit hash c4b68dcd108e497fe95b117fec56942d9af448b1) and p4fmsynth was changed after. Be sure to use the plotting tool to make sense of these, FM synthesis can be really hard to predict.

1 - Square into Sine

(WaveformKind::Square, 440.0),
(WaveformKind::Sine, 440.0),

Explained: When the square is 1 (first 1/2 of the cycle) it adds 440Hz to the sine making it 880Hz. But when it is 0 (second 1/2 of the cycle) it subtracts 440Hz making it 0Hz

2 - Square into Sine with wobble

(WaveformKind::Sine, 4.4),
(WaveformKind::Square, 440.0),
(WaveformKind::Sine, 440.0),

Same as previous example except the 4.4Hz sine controlling the square makes the waveform 'wobble'

xenon/soundtests