diff --git a/CHANGELOG.md b/CHANGELOG.md
index 63faa80..03cf51f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,8 +8,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
-- Support for *ALAC/AIFF* 
-- New sources:
+- Support for *ALAC/AIFF*
+- New test signal generator sources:
+    - `TestSignal` source generates a sine, triangle, square wave or sawtooth
+      of a given frequency and sample rate.
+    - `Chirp` source generates a sine wave with linearly period over a given
+      frequency range and duration.
+    - `white` and `pink` generate white or pink noise, respectively. These 
+      sources depend on the `rand` crate  and are guarded with the "noise" 
+      feature.
+    - Documentation for the "noise" feature has been added to `lib.rs`.
+- New Fade and Crossfade sources:
     - `fade_out` fades an input out using a linear gain fade.
     - `linear_gain_ramp` applies a linear gain change to a sound over a
       given duration. `fade_out` is implemented as a `linear_gain_ramp` and
diff --git a/src/lib.rs b/src/lib.rs
index 6f6c505..c47eafa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -112,6 +112,15 @@
 //! the number of sinks that can be created (except for the fact that creating too many will slow
 //! down your program).
 //!
+//! 
+//! ## Features 
+//!
+//! Rodio provides several optional features that are guarded with feature gates.
+//!
+//! ### Feature "Noise"
+//!
+//! The "noise" feature adds support for white and pink noise sources. This feature requires the
+//! "rand" crate.
 #![cfg_attr(test, deny(missing_docs))]
 pub use cpal::{
     self, traits::DeviceTrait, Device, Devices, DevicesError, InputDevices, OutputDevices,
diff --git a/src/source/chirp.rs b/src/source/chirp.rs
index 8fabc29..1971c70 100644
--- a/src/source/chirp.rs
+++ b/src/source/chirp.rs
@@ -1,6 +1,6 @@
 //! Chirp/sweep source.
 
-use std::time::Duration;
+use std::{f32::consts::TAU, time::Duration};
 
 use crate::Source;
 
@@ -48,9 +48,11 @@ impl Iterator for Chirp {
 
     fn next(&mut self) -> Option<Self::Item> {
         let i = self.elapsed_samples;
+        let ratio = self.elapsed_samples as f32 / self.total_samples as f32;
         self.elapsed_samples += 1;
-
-        todo!()
+        let freq = self.start_frequency * (1.0 - ratio) + self.end_frequency * ratio;
+        let t = (i as f32 / self.sample_rate() as f32) * TAU * freq;
+        Some( t.sin() )
     }
 }