Unpack an FFT chain into separate demand-rate FFT bin streams

Source: FFTUnpacking.sc

Takes an FFT chain and separates the magnitude and phase data into separate demand-rate streams, for arithmetic manipulation etc.

This is technically a demand-rate UGen. The actual "demand" is usually created by PackFFT later on in the graph, which requests the values in order to re-pack the data. This allows for processing to occur in between...

See also pvcollect, pvcalc and pvcalc2 methods ( in PV_ChainUGen ) which provide convenient ways to process audio in the frequency domain. The help for pvcollect includes notes on efficiency considerations.

chain |
FFT chain |

bufsize |
FFT buffer size |

frombin |
limiting analysis to the bins of interest |

tobin |
limiting analysis to the bins of interest |

A list from DC up to Nyquist of `[mag[0], phase[0], mag[1], phase[1], ... mag[nyquist], phase[nyquist]].`

Note that you do have to decide your FFT buffer size in advance, since this determines how many values the UGen will output.

#magsphases = UnpackFFT(chain, bufsize)

c = Buffer.read(s, Platform.resourceDir +/+ "sounds/a11wlk01.wav"); // This one just drags out various the values and posts them - a little bit pointless! ( x = { var sig, chain, unp; //sig = SinOsc.ar; sig = PlayBuf.ar(1, c, BufRateScale.kr(c), loop: 1); chain = FFT(LocalBuf(1, 1024), sig); // Using the frombin & tobin args makes it much more efficient, limiting analysis to the bins of interest unp = UnpackFFT(chain, b.numFrames, frombin: 0, tobin: 4); // Demand some data from the unpacker. // NOTE: At present, Demand.kr is unable to handle more than 32 inputs, // so using frombin & tobin to limit the number of bins is compulsory. Demand.kr(chain>=0, 0, unp).collect{|anunp, index| anunp.poll(chain>=0, if(index % 2 == 0, "Magnitude", "Phase")+(index/2).floor); }; (sig * 0.1).dup; }.play ) x.free; // Now a simple frequency-domain manipulation, square-rooting the magnitudes AND phases. ( x = { var sig, chain, magsphases, b; b = LocalBuf(1, 1024); sig = PlayBuf.ar(1, c, BufRateScale.kr(c), loop: 1); chain = FFT(b, sig); magsphases = UnpackFFT(chain, b.numFrames); magsphases = magsphases.collect(_.sqrt); PackFFT(chain, b.numFrames, magsphases); Out.ar(0, 0.25 * IFFT(chain).dup); }.play ) x.free;

helpfile source: /usr/local/share/SuperCollider/HelpSource/Classes/UnpackFFT.schelp

link::Classes/UnpackFFT::

link::Classes/UnpackFFT::