docs: fixes spatial source & sink description (was wrong & missing)

src/source/channel_volume.rs

@@ -82,7 +82,6 @@ where
 
     #[inline]
     fn next(&mut self) -> Option<I::Item> {
-        // return value
         let ret = self
             .current_sample
             .map(|sample| sample.amplify(self.channel_volumes[self.current_channel]));

src/source/spatial.rs

@@ -5,8 +5,9 @@ use crate::{Sample, Source};
 
 use super::SeekError;
 
-/// Combines channels in input into a single mono source, then plays that mono sound
-/// to each channel at the volume given for that channel.
+/// A simple spatial audio source. The underlying source is transformed to Mono
+/// and then played in stereo. The left and right channel's volume are amplified
+/// differently depending on the distance of the left and right ear to the source.
 #[derive(Clone)]
 pub struct Spatial<I>
 where

src/spatial_sink.rs

@@ -8,6 +8,9 @@ use crate::source::{SeekError, Spatial};
 use crate::stream::{OutputStreamHandle, PlayError};
 use crate::{Sample, Sink, Source};
 
+/// A sink that allows changing the position of the source and the listeners
+/// ears while playing. The sources played are then transformed to give a simple
+/// spatial effect. See [`Spatial`] for details.
 pub struct SpatialSink {
     sink: Sink,
     positions: Arc<Mutex<SoundPositions>>,