diff --git a/readme.md b/readme.md
index 5b874d1..aae2e38 100644
--- a/readme.md
+++ b/readme.md
@@ -32,3 +32,6 @@ Dependencies
 ------------
 
 This library extends the functionality of the [Teensy Audio Library](http://www.pjrc.com/teensy/td_libs_Audio.html), so you'll need to install it per its instructions.
+
+The floating-point processing takes advantage of the DSP acceleration afforded by the ARM M4F core inside the Teensy 3.5/3.6 processor.  Therefore, it uses `arm_math.h`.  This dependencies is installed automatically when you install the Teensy Audio Library, so you don't need to take any extra steps.  It's there already.
+