audio-midi-shell 0.1.0

Prototyping shell for audio development.
Documentation 
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//! Simple monophonic synthesizer generating a sine wave for each received MIDI note.

use audio_midi_shell::{AudioGenerator, AudioMidiShell};

const SAMPLE_RATE: u32 = 44100;
const BUFFER_SIZE: usize = 1024;
const PROCESS_CHUNK_SIZE: usize = 16;

fn main() -> ! {
    AudioMidiShell::run_forever(
        SAMPLE_RATE,
        BUFFER_SIZE,
        PROCESS_CHUNK_SIZE,
        SineSynth::default(),
    );
}

#[derive(Debug, Default)]
struct SineSynth {
    level: f32,
    phase: f32,
    phase_inc: f32,
}

impl AudioGenerator for SineSynth {
    fn process(&mut self, frames: &mut [[f32; 2]]) {
        for frame in frames {
            let sample = f32::sin(self.phase) * self.level * 0.5;
            frame[0] = sample;
            frame[1] = sample;

            self.phase += self.phase_inc;

            if self.phase > core::f32::consts::TAU {
                self.phase -= core::f32::consts::TAU;
            }
        }
    }

    fn process_midi(&mut self, message: &[u8], _timestamp: u64) {
        match message[0] & 0xF0 {
            0x80 => {
                // Note off
                self.level = 0.0;
            }
            0x90 => {
                // Note on
                self.level = message[2] as f32 / 127.0;
                let frequency = 440.0 * f32::powf(2.0, (message[1] as i32 - 69) as f32 / 12.0);
                self.phase_inc = frequency / SAMPLE_RATE as f32 * core::f32::consts::TAU;
            }
            _ => {}
        };
    }
}