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//! ADSR envelope generator and multi-stage envelopes.
//!
//! Provides standard Attack-Decay-Sustain-Release envelopes with linear
//! segments, plus a flexible multi-stage envelope for arbitrary shapes.
use serde::{Deserialize, Serialize};
use crate::error::{NaadError, Result};
/// Envelope state machine stages.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[non_exhaustive]
pub enum EnvelopeState {
/// Envelope is inactive (output = 0).
Idle,
/// Attack phase (rising from 0 to 1).
Attack,
/// Decay phase (falling from 1 to sustain level).
Decay,
/// Sustain phase (holding at sustain level).
Sustain,
/// Release phase (falling from current to 0).
Release,
}
/// ADSR envelope generator with linear segments.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Adsr {
/// Attack time in seconds.
///
/// Note: modifying this directly bypasses validation. Use the constructor
/// for guaranteed-valid values.
pub attack_time: f32,
/// Decay time in seconds.
///
/// Note: modifying this directly bypasses validation. Use the constructor
/// for guaranteed-valid values.
pub decay_time: f32,
/// Sustain level (0.0 to 1.0).
///
/// Note: modifying this directly bypasses validation. Use the constructor
/// for guaranteed-valid values.
pub sustain_level: f32,
/// Release time in seconds.
///
/// Note: modifying this directly bypasses validation. Use the constructor
/// for guaranteed-valid values.
pub release_time: f32,
/// Sample rate in Hz.
sample_rate: f32,
/// Current envelope state.
state: EnvelopeState,
/// Current output value.
current_value: f32,
/// Value at the start of the release phase.
release_start_value: f32,
/// Time spent in the current stage (in samples).
stage_samples: f32,
}
impl Adsr {
/// Create a new ADSR envelope.
///
/// All times are in seconds. Sustain level is 0.0 to 1.0.
///
/// # Errors
///
/// Returns error if any time is negative or sustain is out of range.
pub fn new(attack: f32, decay: f32, sustain: f32, release: f32) -> Result<Self> {
Self::with_sample_rate(attack, decay, sustain, release, 44100.0)
}
/// Create a new ADSR envelope with an explicit sample rate.
///
/// # Errors
///
/// Returns error if any time is negative, sustain is out of range,
/// or sample_rate is invalid.
pub fn with_sample_rate(
attack: f32,
decay: f32,
sustain: f32,
release: f32,
sample_rate: f32,
) -> Result<Self> {
if attack < 0.0 {
return Err(NaadError::InvalidParameter {
name: "attack".to_string(),
reason: "must be >= 0".to_string(),
});
}
if decay < 0.0 {
return Err(NaadError::InvalidParameter {
name: "decay".to_string(),
reason: "must be >= 0".to_string(),
});
}
if !(0.0..=1.0).contains(&sustain) {
return Err(NaadError::InvalidParameter {
name: "sustain".to_string(),
reason: "must be between 0.0 and 1.0".to_string(),
});
}
if release < 0.0 {
return Err(NaadError::InvalidParameter {
name: "release".to_string(),
reason: "must be >= 0".to_string(),
});
}
if sample_rate <= 0.0 || !sample_rate.is_finite() {
return Err(NaadError::InvalidSampleRate { sample_rate });
}
Ok(Self {
attack_time: attack,
decay_time: decay,
sustain_level: sustain,
release_time: release,
sample_rate,
state: EnvelopeState::Idle,
current_value: 0.0,
release_start_value: 0.0,
stage_samples: 0.0,
})
}
/// Returns the current envelope state.
#[inline]
#[must_use]
pub fn state(&self) -> EnvelopeState {
self.state
}
/// Trigger the envelope (note on).
pub fn gate_on(&mut self) {
self.state = EnvelopeState::Attack;
self.stage_samples = 0.0;
}
/// Release the envelope (note off).
pub fn gate_off(&mut self) {
if self.state != EnvelopeState::Idle {
self.release_start_value = self.current_value;
self.state = EnvelopeState::Release;
self.stage_samples = 0.0;
}
}
/// Generate the next envelope value.
///
/// Returns a value between 0.0 and 1.0.
#[inline]
#[must_use]
pub fn next_value(&mut self) -> f32 {
let sr = self.sample_rate;
match self.state {
EnvelopeState::Idle => {
self.current_value = 0.0;
}
EnvelopeState::Attack => {
let attack_samples = self.attack_time * sr;
if attack_samples <= 0.0 {
self.current_value = 1.0;
self.state = EnvelopeState::Decay;
self.stage_samples = 0.0;
} else {
self.current_value = self.stage_samples / attack_samples;
self.stage_samples += 1.0;
if self.current_value >= 1.0 {
self.current_value = 1.0;
self.state = EnvelopeState::Decay;
self.stage_samples = 0.0;
}
}
}
EnvelopeState::Decay => {
let decay_samples = self.decay_time * sr;
if decay_samples <= 0.0 {
self.current_value = self.sustain_level;
self.state = EnvelopeState::Sustain;
} else {
let progress = self.stage_samples / decay_samples;
self.current_value = 1.0 + (self.sustain_level - 1.0) * progress;
self.stage_samples += 1.0;
if self.current_value <= self.sustain_level {
self.current_value = self.sustain_level;
self.state = EnvelopeState::Sustain;
}
}
}
EnvelopeState::Sustain => {
self.current_value = self.sustain_level;
}
EnvelopeState::Release => {
let release_samples = self.release_time * sr;
if release_samples <= 0.0 {
self.current_value = 0.0;
self.state = EnvelopeState::Idle;
} else {
let progress = self.stage_samples / release_samples;
self.current_value = self.release_start_value * (1.0 - progress);
self.stage_samples += 1.0;
if self.current_value <= 0.0 {
self.current_value = 0.0;
self.state = EnvelopeState::Idle;
}
}
}
}
self.current_value
}
/// Check if the envelope is active (not idle).
#[must_use]
pub fn is_active(&self) -> bool {
self.state != EnvelopeState::Idle
}
}
/// A single segment in a multi-stage envelope.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EnvelopeSegment {
/// Target level for this segment (0.0 to 1.0).
pub target: f32,
/// Duration in seconds.
pub duration: f32,
}
/// Multi-stage envelope with arbitrary segments.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MultiStageEnvelope {
/// The segments of the envelope.
pub segments: Vec<EnvelopeSegment>,
/// Sample rate in Hz.
sample_rate: f32,
/// Current segment index.
current_segment: usize,
/// Current output value.
current_value: f32,
/// Start value of current segment.
segment_start_value: f32,
/// Time spent in current segment (in samples).
stage_samples: f32,
/// Whether the envelope is active.
active: bool,
}
impl MultiStageEnvelope {
/// Create a new multi-stage envelope (defaults to 44100 Hz sample rate).
///
/// # Errors
///
/// Returns error if segments is empty.
pub fn new(segments: Vec<EnvelopeSegment>) -> Result<Self> {
Self::with_sample_rate(segments, 44100.0)
}
/// Create a new multi-stage envelope with an explicit sample rate.
///
/// # Errors
///
/// Returns error if segments is empty or sample_rate is invalid.
pub fn with_sample_rate(segments: Vec<EnvelopeSegment>, sample_rate: f32) -> Result<Self> {
if segments.is_empty() {
return Err(NaadError::InvalidParameter {
name: "segments".to_string(),
reason: "must have at least one segment".to_string(),
});
}
if sample_rate <= 0.0 || !sample_rate.is_finite() {
return Err(NaadError::InvalidSampleRate { sample_rate });
}
Ok(Self {
segments,
sample_rate,
current_segment: 0,
current_value: 0.0,
segment_start_value: 0.0,
stage_samples: 0.0,
active: false,
})
}
/// Start the envelope.
pub fn trigger(&mut self) {
self.current_segment = 0;
self.current_value = 0.0;
self.segment_start_value = 0.0;
self.stage_samples = 0.0;
self.active = true;
}
/// Generate the next envelope value.
#[inline]
#[must_use]
pub fn next_value(&mut self) -> f32 {
if !self.active {
return 0.0;
}
if self.current_segment >= self.segments.len() {
self.active = false;
return 0.0;
}
let seg = &self.segments[self.current_segment];
let seg_samples = seg.duration * self.sample_rate;
if seg_samples <= 0.0 {
self.current_value = seg.target;
self.segment_start_value = self.current_value;
self.current_segment += 1;
self.stage_samples = 0.0;
} else {
let progress = (self.stage_samples / seg_samples).min(1.0);
self.current_value =
self.segment_start_value + (seg.target - self.segment_start_value) * progress;
self.stage_samples += 1.0;
if self.stage_samples >= seg_samples {
self.current_value = seg.target;
self.segment_start_value = self.current_value;
self.current_segment += 1;
self.stage_samples = 0.0;
}
}
self.current_value
}
/// Check if the envelope is active.
#[must_use]
pub fn is_active(&self) -> bool {
self.active
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_adsr_basic() {
let mut env = Adsr::new(0.01, 0.01, 0.5, 0.01).unwrap();
assert!(!env.is_active());
env.gate_on();
assert!(env.is_active());
}
#[test]
fn test_adsr_sustain_holds() {
let mut env = Adsr::new(0.001, 0.001, 0.7, 0.01).unwrap();
env.gate_on();
// Run through attack + decay
for _ in 0..1000 {
let _ = env.next_value();
}
// Should be at sustain level
let val = env.next_value();
assert!(
(val - 0.7).abs() < 0.01,
"sustain should hold at 0.7, got {val}"
);
}
#[test]
fn test_adsr_release_to_zero() {
let mut env = Adsr::new(0.0, 0.0, 1.0, 0.01).unwrap();
env.gate_on();
let _ = env.next_value();
env.gate_off();
for _ in 0..2000 {
let _ = env.next_value();
}
assert!(!env.is_active());
}
#[test]
fn test_invalid_params() {
assert!(Adsr::new(-1.0, 0.0, 0.5, 0.0).is_err());
assert!(Adsr::new(0.0, 0.0, 1.5, 0.0).is_err());
assert!(Adsr::new(0.0, 0.0, -0.1, 0.0).is_err());
}
#[test]
fn test_multi_stage() {
let segments = vec![
EnvelopeSegment {
target: 1.0,
duration: 0.01,
},
EnvelopeSegment {
target: 0.5,
duration: 0.01,
},
EnvelopeSegment {
target: 0.0,
duration: 0.01,
},
];
let mut env = MultiStageEnvelope::new(segments).unwrap();
env.trigger();
assert!(env.is_active());
for _ in 0..5000 {
let _ = env.next_value();
}
assert!(!env.is_active());
}
#[test]
fn test_serde_roundtrip() {
let env = Adsr::new(0.01, 0.1, 0.5, 0.2).unwrap();
let json = serde_json::to_string(&env).unwrap();
let back: Adsr = serde_json::from_str(&json).unwrap();
assert!((env.attack_time - back.attack_time).abs() < f32::EPSILON);
assert!((env.sustain_level - back.sustain_level).abs() < f32::EPSILON);
}
}