diff --git a/Machines/CRTMachine.hpp b/Machines/CRTMachine.hpp
index c58f5d320..ce693f5cc 100644
--- a/Machines/CRTMachine.hpp
+++ b/Machines/CRTMachine.hpp
@@ -14,6 +14,11 @@
 
 namespace CRTMachine {
 
+/*!
+	A CRTMachine::Machine is a mostly-abstract base class for machines that connect to a CRT,
+	that optionally provide a speaker, and that nominate a clock rate and can announce to a delegate
+	should that clock rate change.
+*/
 class Machine {
 	public:
 		virtual void setup_output(float aspect_ratio) = 0;
@@ -24,6 +29,7 @@ class Machine {
 
 		virtual void run_for_cycles(int number_of_cycles) = 0;
 
+		// TODO: sever the clock-rate stuff.
 		virtual double get_clock_rate() = 0;
 		class Delegate {
 			public:
diff --git a/Outputs/Speaker.hpp b/Outputs/Speaker.hpp
index 4bcf10408..41efa5586 100644
--- a/Outputs/Speaker.hpp
+++ b/Outputs/Speaker.hpp
@@ -17,6 +17,14 @@
 
 namespace Outputs {
 
+/*!
+	Provides the base class for an audio output source, with an input rate (the speed at which the source will
+	provide data), an output rate (the speed at which the destination will receive data), a delegate to receive
+	the output and some help for the output in picking an appropriate rate once the input rate is known.
+
+	Intended to be a parent class, allowing descendants to pick the strategy by which input samples are mapped to
+	output samples.
+*/
 class Speaker {
 	public:
 		class Delegate {
@@ -82,6 +90,16 @@ class Speaker {
 		}
 };
 
+/*!
+	A concrete descendant of Speaker that uses a FIR filter to map from input data to output data when scaling
+	and a copy-through buffer when input and output rates are the same.
+
+	Audio sources should use @c Filter as both a template and a parent, implementing at least
+	`get_samples(unsigned int quantity, int16_t *target)` and ideally also `skip_samples(unsigned int quantity)`
+	to provide source data.
+
+	Call `run_for_cycles(n)` to request that the next n cycles of input data are collected.
+*/
 template <class T> class Filter: public Speaker {
 	public:
 		void run_for_cycles(unsigned int input_cycles)
@@ -147,7 +165,7 @@ template <class T> class Filter: public Speaker {
 						if(steps < _number_of_taps)
 						{
 							int16_t *input_buffer = _input_buffer.get();
-							memmove(input_buffer, &input_buffer[steps], sizeof(int16_t)  * ((size_t)_number_of_taps - (size_t)steps));
+							memmove(input_buffer, &input_buffer[steps], sizeof(int16_t) * ((size_t)_number_of_taps - (size_t)steps));
 							_input_buffer_depth -= steps;
 						}
 						else