teensy-audio/effect_bitcrusher.cpp

/* Audio Library for Teensy 3.X
 * Copyright (c) 2014, Jonathan Payne (jon@jonnypayne.com)
 * Based on Effect_Fade by Paul Stoffregen
 * Also samplerate reduction based on Pete Brown's bitcrusher here: 
 * http://10rem.net/blog/2013/01/13/a-simple-bitcrusher-and-sample-rate-reducer-in-cplusplus-for-a-windows-store-app
 *
 * Development of this audio library was funded by PJRC.COM, LLC by sales of
 * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
 * open source software by purchasing Teensy or other PJRC products.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice, development funding notice, and this permission
 * notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "effect_bitcrusher.h"

void AudioEffectBitcrusher::update(void)
{
	audio_block_t *block;
	uint32_t i;
	uint32_t sampleSquidge, sampleSqueeze; //squidge is bitdepth, squeeze is for samplerate
			
	if (crushBits == 16 && sampleStep <= 1) {
		// nothing to do. Output is sent through clean, then exit the function
		block = receiveReadOnly();
		if (!block) return;
		transmit(block);
		release(block);
		return;
	}
	// start of processing functions. Could be more elegant based on external
	// functions but left like this to enable code optimisation later.
	block = receiveWritable();
	if (!block) return;

	if (sampleStep <= 1) { //no sample rate mods, just crush the bitdepth.
		for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
			// shift bits right to cut off fine detail sampleSquidge is a
			// uint32 so sign extension will not occur, fills with zeroes.
			sampleSquidge = block->data[i] >> (16-crushBits);
			// shift bits left again to regain the volume level.
			// fills with zeroes.
		 	block->data[i] = sampleSquidge << (16-crushBits);
		}
	} else if (crushBits == 16) { //bitcrusher not being used, samplerate mods only.
		i=0;
		while (i < AUDIO_BLOCK_SAMPLES) {
			// save the root sample. this will pick up a root
			// sample every _sampleStep_ samples.
			sampleSqueeze = block->data[i];
			for (int j = 0; j < sampleStep && i < AUDIO_BLOCK_SAMPLES; j++) {
 				// for each repeated sample, paste in the current
				// root sample, then move onto the next step.
				block->data[i] = sampleSqueeze;
				i++;
			}
		}
	} else {           //both being used. crush those bits and mash those samples.
		i=0;
		while (i < AUDIO_BLOCK_SAMPLES) {
			// save the root sample. this will pick up a root sample
			// every _sampleStep_ samples.
			sampleSqueeze = block->data[i];
			for (int j = 0; j < sampleStep && i < AUDIO_BLOCK_SAMPLES; j++) {
 				// shift bits right to cut off fine detail sampleSquidge
				// is a uint32 so sign extension will not occur, fills
				// with zeroes.
				sampleSquidge = sampleSqueeze >> (16-crushBits);
 				// shift bits left again to regain the volume level.
				// fills with zeroes. paste into buffer sample +
				// sampleStep offset.
				block->data[i] = sampleSquidge << (16-crushBits);
				i++;
			}
		}
	}
	transmit(block);
	release(block);
}