SampleHuffman Class Reference

A sample player for samples encoded with Huffman compression. More...

#include <SampleHuffman.h>

Public Member Functions
	SampleHuffman (uint8_t const *SOUNDDATA, int16_t const *HUFFMAN_DATA, uint32_t const SOUNDDATA_BITS)
	Constructor. More...
int16_t	next ()
	Update and return the next audio sample. More...
void	setLoopingOn ()
	Turns looping on, with the whole sample length as the loop range.
void	setLoopingOff ()
	Turns looping off.
void	start ()
	Sets the playhead to the beginning of the sample.

Detailed Description

A sample player for samples encoded with Huffman compression.

This class and the audio2huff.py script are adapted from "audioout", an Arduino sketch by Thomas Grill, 2011 http//grrrr.org

Huffman decoding is used on sample differentials, saving 50-70% of space for 8 bit data, depending on the sample rate.

This implementation just plays back one sample each time next() is called, with no speed or other adjustments. It's slow, so it's likely you will only be able to play one sound at a time.

Audio data, Huffman decoder table, sample rate and bit depth are defined in a sounddata.h header file. This file can be generated for a sound file with the accompanying Python script audio2huff.py, in Mozzi/extras/python/

Invoke with: python audio2huff.py –sndfile=arduinosnd.wav –hdrfile=sounddata.h –bits=8 –name=soundtablename

You can resample and dither your audio file with SOX, e.g. to 8 bits depth @ Mozzi's 16384 Hz sample rate: sox fullglory.wav -b 8 -r 16384 arduinosnd.wav

Alternatively you can export a sound from Audacity, which seems to have less noticeable or no dithering, using Project Rate 16384 Hz and these output options: Other uncompressed files, Header: WAV(Microsoft), Encoding: Unsigned 8 bit PCM

The header file contains two lengthy arrays: One is "SOUNDDATA" which must fit into Flash RAM (available in total: 32k for ATMega328) The other is "HUFFMAN" which must also fit into Flash RAM

Definition at line 49 of file SampleHuffman.h.

Constructor & Destructor Documentation

SampleHuffman()

SampleHuffman::SampleHuffman ( uint8_t const *  SOUNDDATA, int16_t const *  HUFFMAN_DATA, uint32_t const  SOUNDDATA_BITS  )

inline

Constructor.

Parameters

SOUNDDATA	the name of the SOUNDDATA table in the huffman sample .h file
HUFFMAN_DATA	the name of the HUFFMAN table in the huffman sample .h file
SOUNDDATA_BITS	from the huffman sample .h file

Definition at line 59 of file SampleHuffman.h.

Member Function Documentation

next()

int16_t SampleHuffman::next ( )

inline

Update and return the next audio sample.

So far it just plays back one sample at a time without any variable tuning or speed.

Returns

the next audio sample

Note

timing: about 5 to 40 us, varies continuously depending on data

Definition at line 70 of file SampleHuffman.h.