kira 0.12.0

Expressive audio library for games
Documentation 
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//! Reduces (or increases) the dynamic range of audio.

// Loosely based on https://www.musicdsp.org/en/latest/Effects/204-simple-compressor-class-c.html

mod builder;
mod handle;

pub use builder::*;
pub use handle::*;

use std::time::Duration;

use crate::{
	Decibels, Mix, Parameter,
	command::{ValueChangeCommand, read_commands_into_parameters},
	command_writers_and_readers,
	frame::Frame,
	info::Info,
};

use super::Effect;

struct Compressor {
	command_readers: CommandReaders,
	threshold: Parameter,
	ratio: Parameter,
	attack_duration: Parameter<Duration>,
	release_duration: Parameter<Duration>,
	makeup_gain: Parameter<Decibels>,
	mix: Parameter<Mix>,
	envelope_follower: [f32; 2],
}

impl Compressor {
	#[must_use]
	fn new(builder: CompressorBuilder, command_readers: CommandReaders) -> Self {
		Self {
			command_readers,
			threshold: Parameter::new(builder.threshold, CompressorBuilder::DEFAULT_THRESHOLD),
			ratio: Parameter::new(builder.ratio, CompressorBuilder::DEFAULT_RATIO),
			attack_duration: Parameter::new(
				builder.attack_duration,
				CompressorBuilder::DEFAULT_ATTACK_DURATION,
			),
			release_duration: Parameter::new(
				builder.release_duration,
				CompressorBuilder::DEFAULT_RELEASE_DURATION,
			),
			makeup_gain: Parameter::new(
				builder.makeup_gain,
				CompressorBuilder::DEFAULT_MAKEUP_GAIN,
			),
			mix: Parameter::new(builder.mix, CompressorBuilder::DEFAULT_MIX),
			envelope_follower: [0.0; 2],
		}
	}
}

impl Effect for Compressor {
	fn on_start_processing(&mut self) {
		read_commands_into_parameters!(
			self,
			threshold,
			ratio,
			attack_duration,
			release_duration,
			makeup_gain,
			mix,
		);
	}

	fn process(&mut self, input: &mut [Frame], dt: f64, info: &Info) {
		self.threshold.update(dt * input.len() as f64, info);
		self.ratio.update(dt * input.len() as f64, info);
		self.attack_duration.update(dt * input.len() as f64, info);
		self.release_duration.update(dt * input.len() as f64, info);
		self.makeup_gain.update(dt * input.len() as f64, info);
		self.mix.update(dt * input.len() as f64, info);

		let threshold = self.threshold.value() as f32;
		let ratio = self.ratio.value() as f32;
		let attack_duration = self.attack_duration.value();
		let release_duration = self.release_duration.value();

		let num_frames = input.len();
		for (i, frame) in input.iter_mut().enumerate() {
			let time_in_chunk = (i + 1) as f64 / num_frames as f64;
			let makeup_gain = self.makeup_gain.interpolated_value(time_in_chunk);
			let mix = self.mix.interpolated_value(time_in_chunk).0.clamp(0.0, 1.0);

			let input_decibels = [
				20.0 * frame.left.abs().log10(),
				20.0 * frame.right.abs().log10(),
			];
			let over_decibels = input_decibels.map(|input| (input - threshold).max(0.0));
			for (i, envelope_follower) in self.envelope_follower.iter_mut().enumerate() {
				let duration = if *envelope_follower > over_decibels[i] {
					release_duration
				} else {
					attack_duration
				};
				let speed = (-1.0 / (duration.as_secs_f64() / dt)).exp();
				*envelope_follower =
					over_decibels[i] + speed as f32 * (*envelope_follower - over_decibels[i]);
			}
			let gain_reduction = self
				.envelope_follower
				.map(|envelope_follower| envelope_follower * ((1.0 / ratio) - 1.0));
			let amplitude =
				gain_reduction.map(|gain_reduction| 10.0f32.powf(gain_reduction / 20.0));
			let makeup_gain_linear = 10.0f32.powf(makeup_gain.0 / 20.0);
			let output = Frame {
				left: amplitude[0] * frame.left,
				right: amplitude[1] * frame.right,
			} * makeup_gain_linear;

			*frame = output * mix.sqrt() + *frame * (1.0 - mix).sqrt()
		}
	}
}

command_writers_and_readers! {
	set_threshold: ValueChangeCommand<f64>,
	set_ratio: ValueChangeCommand<f64>,
	set_attack_duration: ValueChangeCommand<Duration>,
	set_release_duration: ValueChangeCommand<Duration>,
	set_makeup_gain: ValueChangeCommand<Decibels>,
	set_mix: ValueChangeCommand<Mix>,
}