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#![forbid(unsafe_code)]
#![deny(
missing_docs,
missing_debug_implementations,
rust_2018_idioms,
future_incompatible,
bare_trait_objects,
elided_lifetimes_in_paths,
trivial_casts,
unreachable_pub
)]
use sample::{Frame, Sample, SignedSample};
#[derive(Debug, Clone, PartialEq)]
pub struct NoiseGate<S> {
pub open_threshold: S,
pub release_time: usize,
state: State,
}
impl<S> NoiseGate<S> {
pub const fn new(open_threshold: S, release_time: usize) -> Self {
NoiseGate {
open_threshold,
release_time,
state: State::Closed,
}
}
pub fn is_open(&self) -> bool {
match self.state {
State::Open | State::Closing { .. } => true,
State::Closed => false,
}
}
pub fn is_closed(&self) -> bool { !self.is_open() }
}
impl<S: Sample> NoiseGate<S> {
pub fn process_frames<K, F>(&mut self, frames: &[F], sink: &mut K)
where
F: Frame<Sample = S>,
K: Sink<F>,
{
for &frame in frames {
let previously_open = self.is_open();
self.state = next_state(
self.state,
frame,
self.open_threshold,
self.release_time,
);
if self.is_open() {
sink.record(frame);
} else if previously_open {
sink.end_of_transmission();
}
}
}
}
fn below_threshold<F>(frame: F, threshold: F::Sample) -> bool
where
F: Frame,
{
let threshold = abs(threshold.to_signed_sample());
let negated_threshold =
F::Sample::equilibrium().to_signed_sample() - threshold;
frame
.channels()
.map(|sample| sample.to_signed_sample())
.all(|sample| negated_threshold < sample && sample < threshold)
}
fn abs<S: SignedSample>(sample: S) -> S {
let zero = S::equilibrium();
if sample >= zero {
sample
} else {
-sample
}
}
#[derive(Debug, Copy, Clone, PartialEq)]
enum State {
Open,
Closing { remaining_samples: usize },
Closed,
}
fn next_state<F>(
state: State,
frame: F,
open_threshold: F::Sample,
release_time: usize,
) -> State
where
F: Frame,
{
match state {
State::Open => {
if below_threshold(frame, open_threshold) {
State::Closing {
remaining_samples: release_time,
}
} else {
State::Open
}
},
State::Closing { remaining_samples } => {
if below_threshold(frame, open_threshold) {
if remaining_samples == 0 {
State::Closed
} else {
State::Closing {
remaining_samples: remaining_samples - 1,
}
}
} else {
State::Open
}
},
State::Closed => {
if below_threshold(frame, open_threshold) {
State::Closed
} else {
State::Open
}
},
}
}
pub trait Sink<F> {
fn record(&mut self, frame: F);
fn end_of_transmission(&mut self);
}
#[cfg(test)]
mod tests {
use super::*;
const OPEN_THRESHOLD: i16 = 100;
const RELEASE_TIME: usize = 5;
macro_rules! test_state_transition {
($name:ident: $from:expr, $sample:expr => $expected:expr) => {
#[test]
fn $name() {
let start: State = $from;
let expected: State = $expected;
let frame: [i16; 1] = [$sample];
let got =
next_state(start, frame, OPEN_THRESHOLD, RELEASE_TIME);
assert_eq!(got, expected);
}
};
}
test_state_transition!(open_to_open: State::Open, 101 => State::Open);
test_state_transition!(open_to_closing: State::Open, 40 => State::Closing { remaining_samples: RELEASE_TIME });
test_state_transition!(closing_to_closed: State::Closing { remaining_samples: 0 }, 40 => State::Closed);
test_state_transition!(closing_to_closing: State::Closing { remaining_samples: 1 }, 40 => State::Closing { remaining_samples: 0 });
test_state_transition!(reopen_when_closing: State::Closing { remaining_samples: 1 }, 101 => State::Open);
test_state_transition!(closed_to_closed: State::Closed, 40 => State::Closed);
test_state_transition!(closed_to_open: State::Closed, 101 => State::Open);
}