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copied!<p>Here's a real-world example: A snippet of c++ that uses Accelerate's vDSP fft routines to do autocorrelation on the Remote IO audio unit's input. Using this framework is pretty complicated, but the documentation isn't <em>too</em> bad.</p> <pre><code>OSStatus DSPCore::initialize (double _sampleRate, uint16_t _bufferSize) { sampleRate = _sampleRate; bufferSize = _bufferSize; peakIndex = 0; frequency = 0.f; uint32_t maxFrames = getMaxFramesPerSlice(); displayData = (float*)malloc(maxFrames*sizeof(float)); bzero(displayData, maxFrames*sizeof(float)); log2n = log2f(maxFrames); n = 1 << log2n; assert(n == maxFrames); nOver2 = maxFrames/2; A.realp = (float*)malloc(nOver2 * sizeof(float)); A.imagp = (float*)malloc(nOver2 * sizeof(float)); FFTSetup fftSetup = vDSP_create_fftsetup(log2n, FFT_RADIX2); return noErr; } void DSPCore::Render(uint32_t numFrames, AudioBufferList *ioData) { bufferSize = numFrames; float ln = log2f(numFrames); //vDSP autocorrelation //convert real input to even-odd vDSP_ctoz((COMPLEX*)ioData->mBuffers[0].mData, 2, &A, 1, numFrames/2); memset(ioData->mBuffers[0].mData, 0, ioData->mBuffers[0].mDataByteSize); //fft vDSP_fft_zrip(fftSetup, &A, 1, ln, FFT_FORWARD); // Absolute square (equivalent to mag^2) vDSP_zvmags(&A, 1, A.realp, 1, numFrames/2); bzero(A.imagp, (numFrames/2) * sizeof(float)); // Inverse FFT vDSP_fft_zrip(fftSetup, &A, 1, ln, FFT_INVERSE); //convert complex split to real vDSP_ztoc(&A, 1, (COMPLEX*)displayData, 2, numFrames/2); // Normalize float scale = 1.f/displayData[0]; vDSP_vsmul(displayData, 1, &scale, displayData, 1, numFrames); // Naive peak-pick: find the first local maximum peakIndex = 0; for (size_t ii=1; ii < numFrames-1; ++ii) { if ((displayData[ii] > displayData[ii-1]) && (displayData[ii] > displayData[ii+1])) { peakIndex = ii; break; } } // Calculate frequency frequency = sampleRate / peakIndex + quadInterpolate(&displayData[peakIndex-1]); bufferSize = numFrames; for (int ii=0; ii<ioData->mNumberBuffers; ++ii) { bzero(ioData->mBuffers[ii].mData, ioData->mBuffers[ii].mDataByteSize); } } </code></pre>

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