## the rolloff (5) in Hz. This indicates the frequency under which 95% of the energy is included.
## the flatness (6) in dB. This is the ratio of geometric mean of the magnitude, over the arithmetic mean of the magnitudes. It yields a very approximate measure on how noisy a signal is.
## the crest (7) in dB. This is the ratio of the loudest magnitude over the RMS of the whole frame. A high number is an indication of a loud peak poking out from the overal spectral curve.
## the crest (7) in dB. This is the ratio of the loudest magnitude over the RMS of the whole frame. A high number is an indication of a loud peak poking out from the overal spectral curve.::
The drawings in Peeters 2003 (http://recherche.ircam.fr/anasyn/peeters/ARTICLES/Peeters_2003_cuidadoaudiofeatures.pdf) are useful, as are the commented examples below. For the mathematically-inclined reader, the tutorials and code offered here (https://www.audiocontentanalysis.org/) are interesting to further the understanding.
::
The drawings in Peeters 2003 (http://recherche.ircam.fr/anasyn/peeters/ARTICLES/Peeters_2003_cuidadoaudiofeatures.pdf) are useful, as are the commented examples below. For the mathematically-inclined reader, the tutorials and code offered here (https://www.audiocontentanalysis.org/) are interesting to further the understanding. For examples of the impact of computing the moments in power magnitudes, and/or in exponential frequency scale, please refer to the LINK::Classes/FluidSpectralShape:: helpfile.
The process will return a multichannel buffer with the seven channels per input channel, each containing the 7 shapes. Each sample represents a value, which is every hopSize.
@ -65,7 +64,7 @@ ARGUMENT:: rolloffPercent
This sets the percentage of the frame's energy that will be reported as the rolloff frequency. The default is 95%.
ARGUMENT:: unit
The frequency unit for the spectral shapes to be computed upon, and outputted at. The default (0) is in Hertz and computes the moments on a linear spectrum. The alternative is in MIDI note numbers(1), which compute the momontes on an exponential spectrum.
The frequency unit for the spectral shapes to be computed upon, and outputted at. The default (0) is in Hertz and computes the moments on a linear spectrum. The alternative is in MIDI note numbers(1), which compute the moments on an exponential spectrum.
ARGUMENT:: power
This flag sets the scaling of the magnitudes in the moment calculation. It uses either its amplitude (0, by default) or its power (1).
This sets the percentage of the frame's energy that will be reported as the rolloff frequency. The default is 95%.
ARGUMENT:: unit
The frequency unit for the spectral shapes to be computed upon, and outputted at. The default (0) is in Hertz and computes the moments on a linear spectrum. The alternative is in MIDI note numbers(1), which compute the momontes on an exponential spectrum.
The frequency unit for the spectral shapes to be computed upon, and outputted at. The default (0) is in Hertz and computes the moments on a linear spectrum. The alternative is in MIDI note numbers(1), which compute the moments on an exponential spectrum.
ARGUMENT:: power
This flag sets the scaling of the magnitudes in the moment calculation. It uses either its amplitude (0, by default) or its power (1).
@ -250,3 +250,76 @@ x.set(\freq, 8800)
// we can observe that the linear spread is kept the same, since there is the same linear distance in Hz between our frequencies. Skewness is a good indication here of where we are in the spectrum with the shape.
::
STRONG::A few notes on the impact of the scale options::
CODE::
// The computation of the centroids and other moments can also be done considering a logarithmic pitch scale, and/or the power of the magnitudes. This yields values that are more in line with the expectation of the users of equalisers for instance, where the shape is often drawn and described in logairhmic terms, i.e. dB per octave.
// For instance, compare the values of the centroid and the spread in both scales:
(
{
var source = BPF.ar(PinkNoise.ar(0.1),MouseX.kr().exprange(300,3000).poll(1,label: "filter frequency"), 0.5);
// The logarythmic unit is in semitones. To convert, either divide by 12 to get the octave of one standard deviation, or divide by 6 to get the width of the filter in octaves. One clear observation is that the width is now in a range that scales with what we hear, growing fourfold as the filter goes from resonating to more broadband.
// An example of productive mapping between filters parameters and logarithmic centroid values allows to make a simple automatic subtractive noise resynthesis
// load a beat
b = Buffer.read(s,File.realpath(FluidSpectralShape.class.filenameSymbol).dirname.withTrailingSlash ++ "../AudioFiles/Nicol-LoopE-M.wav");
Pierre Alexandre Tremblay
5 years ago