/* * File: PaulDither.cpp * * Version: 1.0 * * Created: 11/17/16 * * Copyright: Copyright © 2016 Airwindows, All Rights Reserved * * Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Computer, Inc. ("Apple") in * consideration of your agreement to the following terms, and your use, installation, modification * or redistribution of this Apple software constitutes acceptance of these terms. 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It won't keep assigning //it to 0 for every sample, it's as if the declaration doesn't exist in this context, //but it lets me add this denormalization fix in a single place rather than updating //it in three different locations. The variable isn't thread-safe but this is only //a random seed and we can share it with whatever. noisesource = noisesource % 1700021; noisesource++; int residue = noisesource * noisesource; residue = residue % 170003; residue *= residue; residue = residue % 17011; residue *= residue; residue = residue % 1709; residue *= residue; residue = residue % 173; residue *= residue; residue = residue % 17; double applyresidue = residue; applyresidue *= 0.00000001; applyresidue *= 0.00000001; inputSample = applyresidue; //this denormalization routine produces a white noise at -300 dB which the noise //shaping will interact with to produce a bipolar output, but the noise is actually //all positive. That should stop any variables from going denormal, and the routine //only kicks in if digital black is input. As a final touch, if you save to 24-bit //the silence will return to being digital black again. } inputSample *= 8388608.0; //0-1 is now one bit, now we dither currentDither = (rand()/(double)RAND_MAX); inputSample += currentDither; inputSample -= previousDither; inputSample = floor(inputSample); previousDither = currentDither; //Paul Frindle: It's true that the dither itself can sound different //if it's given a different freq response and you get to hear it. //The one we use most is triangular single pole high pass dither. //It not freq bent enough sound odd, but is slightly less audible than //flat dither. It can also be easily made by taking one sample of dither //away from the previous one - this gives you the triangular PDF and the //filtering in one go :-) inputSample /= 8388608.0; *destP = inputSample; sourceP += inNumChannels; destP += inNumChannels; } }