TITLE:: FluidBufMFCC
SUMMARY:: Mel-Frequency Cepstral Coefficients as Spectral Descriptors on a Buffer
CATEGORIES:: Libraries>FluidDecomposition
RELATED:: Guides/FluCoMa, Guides/FluidDecomposition, Classes/FluidBufMelBands

DESCRIPTION::
This class implements a classic spectral descriptor, the Mel-Frequency Cepstral Coefficients (https://en.wikipedia.org/wiki/Mel-frequency_cepstrum). The input is first filtered in to STRONG::numBands:: perceptually-spaced bands, as in LINK::Classes/FluidMelBands::. It is then analysed into STRONG::numCoefs:: number of cepstral coefficients. It has the avantage of being amplitude invarient, except for the first coefficient. It is part of the Fluid Decomposition Toolkit of the FluCoMa project.FOOTNOTE:: This was made possible thanks to the FluCoMa project ( http://www.flucoma.org/ ) funded by the European Research Council ( https://erc.europa.eu/ ) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 725899).::

The process will return a single multichannel buffer of STRONG::numCoefs:: per input channel. Each frame represents a value, which is every hopSize.

CLASSMETHODS::

METHOD:: process
	This is the method that calls for the spectral shape descriptors to be calculated on a given source buffer.

ARGUMENT:: server
	The server on which the buffers to be processed are allocated.

ARGUMENT:: source
	The index of the buffer to use as the source material to be described through the various descriptors. The different channels of multichannel buffers will be processing sequentially.

ARGUMENT:: startFrame
	Where in the srcBuf should the process start, in sample.

ARGUMENT:: numFrames
	How many frames should be processed.

ARGUMENT:: startChan
	For multichannel srcBuf, which channel should be processed first.

ARGUMENT:: numChans
	For multichannel srcBuf, how many channel should be processed.

ARGUMENT:: features
	The destination buffer for the numCoefs coefficients describing the spectral shape.

ARGUMENT:: numCoefs
	The number of cepstral coefficients to be outputed. It will decide how many channels are produce per channel of the source.

ARGUMENT:: numBands
	The number of bands that will be perceptually equally distributed between STRONG::minFreq:: and STRONG::maxFreq::.

ARGUMENT:: minFreq
	The lower boundary of the lowest band of the model, in Hz.

ARGUMENT:: maxFreq
	The highest boundary of the highest band of the model, in Hz.

ARGUMENT:: windowSize
	The window size. As MFCC computation relies on spectral frames, we need to decide what precision we give it spectrally and temporally, in line with Gabor Uncertainty principles. http://www.subsurfwiki.org/wiki/Gabor_uncertainty

ARGUMENT:: hopSize
	The window hop size. As MFCC computation relies on spectral frames, we need to move the window forward. It can be any size but low overlap will create audible artefacts.

ARGUMENT:: fftSize
	The inner FFT/IFFT size. It should be at least 4 samples long, at least the size of the window, and a power of 2. Making it larger allows an oversampling of the spectral precision.

ARGUMENT:: action
	A Function to be evaluated once the offline process has finished and all Buffer's instance variables have been updated on the client side. The function will be passed [features] as an argument.

RETURNS::
	Nothing, as the destination buffer is declared in the function call.

EXAMPLES::

code::
// create some buffers
(
b = Buffer.read(s,File.realpath(FluidBufMFCC.class.filenameSymbol).dirname.withTrailingSlash ++ "../AudioFiles/Nicol-LoopE-M.wav");
c = Buffer.new(s);
)

// run the process with basic parameters
(
Routine{
	t = Main.elapsedTime;
	FluidBufMFCC.process(s, b, features: c);
	(Main.elapsedTime - t).postln;
}.play
)

// listen to the source and look at the buffer
b.play;
c.plot(separately:true)
::

STRONG::A stereo buffer example.::
CODE::

// load two very different files
(
b = Buffer.read(s,File.realpath(FluidBufSpectralShape.class.filenameSymbol).dirname.withTrailingSlash ++ "../AudioFiles/Tremblay-SA-UprightPianoPedalWide.wav");
c = Buffer.read(s,File.realpath(FluidBufSpectralShape.class.filenameSymbol).dirname.withTrailingSlash ++ "../AudioFiles/Tremblay-AaS-AcousticStrums-M.wav");
)

// composite one on left one on right as test signals
FluidBufCompose.process(s, c, numFrames:b.numFrames, startFrame:555000,destStartChan:1, destination:b)
b.play

// create a buffer as destinations
c = Buffer.new(s);

//run the process on them
(
Routine{
    t = Main.elapsedTime;
    FluidBufMFCC.process(s, b, numCoefs:5, features: c);
    (Main.elapsedTime - t).postln;
}.play
)

// look at the buffer: 5 coefs for left, then 5 coefs for right (the first of each is linked to the loudness)
c.plot(separately:true)
::