[Discussion] Minimize unnecessary resampling

examples/mix_multiple_sources.rs

@@ -1,11 +1,12 @@
+use rodio::constants::DEFAULT_SAMPLE_RATE;
 use rodio::mixer;
 use rodio::source::{SineWave, Source};
 use std::error::Error;
 use std::time::Duration;
 
 fn main() -> Result<(), Box<dyn Error>> {
     // Construct a dynamic controller and mixer, stream_handle, and sink.
-    let (controller, mixer) = mixer::mixer::<f32>(2, 44_100);
+    let (controller, mixer) = mixer::mixer::<f32>(2, DEFAULT_SAMPLE_RATE);
     let stream_handle = rodio::OutputStreamBuilder::open_default_stream()?;
     let sink = rodio::Sink::connect_new(&stream_handle.mixer());
 

examples/noise_generator.rs

@@ -1,5 +1,6 @@
 //! Noise generator example. Use the "noise" feature to enable the noise generator sources.
 
+use rodio::constants::DEFAULT_SAMPLE_RATE;
 use std::error::Error;
 
 #[cfg(feature = "noise")]
@@ -14,7 +15,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let interval_duration = Duration::from_millis(1500);
 
     stream_handle.mixer().add(
-        white(cpal::SampleRate(48000))
+        white(cpal::SampleRate(DEFAULT_SAMPLE_RATE))
             .amplify(0.1)
             .take_duration(noise_duration),
     );
@@ -23,7 +24,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     thread::sleep(interval_duration);
 
     stream_handle.mixer().add(
-        pink(cpal::SampleRate(48000))
+        pink(cpal::SampleRate(DEFAULT_SAMPLE_RATE))
             .amplify(0.1)
             .take_duration(noise_duration),
     );

examples/signal_generator.rs

@@ -1,5 +1,6 @@
 //! Test signal generator example.
 
+use rodio::constants::DEFAULT_SAMPLE_RATE;
 use std::error::Error;
 
 fn main() -> Result<(), Box<dyn Error>> {
@@ -11,7 +12,7 @@ fn main() -> Result<(), Box<dyn Error>> {
 
     let test_signal_duration = Duration::from_millis(1000);
     let interval_duration = Duration::from_millis(1500);
-    let sample_rate = cpal::SampleRate(48000);
+    let sample_rate = cpal::SampleRate(DEFAULT_SAMPLE_RATE);
 
     println!("Playing 1000 Hz tone");
     stream_handle.mixer().add(

src/constants.rs

@@ -0,0 +1,5 @@
+//! Rodio common constants
+
+/// The sample rate (Hz) output stream uses by default.
+/// Prefer this one in the processing chain to minimize sample rate conversions.
+pub const DEFAULT_SAMPLE_RATE: u32 = 44_100;

src/conversions/mod.rs

@@ -2,7 +2,6 @@
 This module contains function that will convert from one PCM format to another.
 
 This includes conversion between sample formats, channels or sample rates.
-
 */
 
 pub use self::channels::ChannelCountConverter;

src/lib.rs

@@ -161,6 +161,7 @@ mod spatial_sink;
 mod stream;
 
 pub mod buffer;
+pub mod constants;
 pub mod decoder;
 pub mod mixer;
 pub mod queue;

src/source/empty.rs

@@ -1,9 +1,9 @@
 use std::marker::PhantomData;
 use std::time::Duration;
 
-use crate::{Sample, Source};
-
 use super::SeekError;
+use crate::constants::DEFAULT_SAMPLE_RATE;
+use crate::{Sample, Source};
 
 /// An empty source.
 #[derive(Debug, Copy, Clone)]
@@ -50,7 +50,7 @@ where
 
     #[inline]
     fn sample_rate(&self) -> u32 {
-        48000
+        DEFAULT_SAMPLE_RATE
     }
 
     #[inline]

src/source/empty_callback.rs

@@ -1,9 +1,9 @@
 use std::marker::PhantomData;
 use std::time::Duration;
 
-use crate::{Sample, Source};
-
 use super::SeekError;
+use crate::constants::DEFAULT_SAMPLE_RATE;
+use crate::{Sample, Source};
 
 /// An empty source which executes a callback function
 pub struct EmptyCallback<S> {
@@ -53,7 +53,7 @@ where
 
     #[inline]
     fn sample_rate(&self) -> u32 {
-        48000
+        DEFAULT_SAMPLE_RATE
     }
 
     #[inline]

src/source/sine.rs

@@ -1,13 +1,13 @@
-use std::time::Duration;
-
+use crate::constants::DEFAULT_SAMPLE_RATE;
 use crate::source::{Function, SignalGenerator};
 use crate::Source;
+use std::time::Duration;
 
 use super::SeekError;
 
 /// An infinite source that produces a sine.
 ///
-/// Always has a sample rate of 48kHz and one channel.
+/// Always has default sample rate.
 ///
 /// This source is a thin interface on top of `SignalGenerator` provided for
 /// your convenience.
@@ -17,12 +17,10 @@ pub struct SineWave {
 }
 
 impl SineWave {
-    const SAMPLE_RATE: u32 = 48000;
-
     /// The frequency of the sine.
     #[inline]
     pub fn new(freq: f32) -> SineWave {
-        let sr = cpal::SampleRate(Self::SAMPLE_RATE);
+        let sr = cpal::SampleRate(DEFAULT_SAMPLE_RATE);
         SineWave {
             test_sine: SignalGenerator::new(sr, freq, Function::Sine),
         }
@@ -51,7 +49,7 @@ impl Source for SineWave {
 
     #[inline]
     fn sample_rate(&self) -> u32 {
-        Self::SAMPLE_RATE
+        self.test_sine.sample_rate()
     }
 
     #[inline]

src/stream.rs

@@ -3,6 +3,7 @@ use std::marker::Sync;
 use std::sync::Arc;
 use std::{error, fmt};
 
+use crate::constants::DEFAULT_SAMPLE_RATE;
 use crate::decoder;
 use crate::mixer::{mixer, Mixer, MixerSource};
 use crate::sink::Sink;
@@ -12,7 +13,7 @@ use cpal::{
     SupportedBufferSize,
 };
 
-const HZ_44100: cpal::SampleRate = cpal::SampleRate(44_100);
+const HZ_44100: cpal::SampleRate = cpal::SampleRate(DEFAULT_SAMPLE_RATE);
 
 /// `cpal::Stream` container.
 /// Use `mixer()` method to control output.