The Alternative Csound Reference Manual
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# specptrk

spectrk -- Estimates the pitch of the most prominent complex tone in the spectrum.

## Description

Estimate the pitch of the most prominent complex tone in the spectrum.

## Syntax

koct, kamp specptrk wsig, kvar, ilo, ihi, istr, idbthresh, inptls, irolloff [, iodd] [, iconfs] [, interp] [, ifprd] [, iwtflg]

## Initialization

ilo, ihi, istr -- pitch range conditioners (low, high, and starting) expressed in decimal octave form.

idbthresh -- energy threshold (in decibels) for pitch tracking to occur. Once begun, tracking will be continuous until the energy falls below one half the threshold (6 dB down), whence the koct and kamp outputs will be zero until the full threshold is again surpassed. idbthresh is a guiding value. At initialization it is first converted to the idbout mode of the source spectrum (and the 6 dB down point becomes .5, .25, or 1/root 2 for modes 0, 2 and 3). The values are also further scaled to allow for the weighted partial summation used during correlation.The actual thresholding is done using the internal weighted and summed kamp value that is visible as the second output parameter.

inptls, irolloff -- number of harmonic partials used as a matching template in the spectrally-based pitch detection, and an amplitude rolloff for the set expressed as some fraction per octave (linear, so don't roll off to negative). Since the partials and rolloff fraction can affect the pitch following, some experimentation will be useful: try 4 or 5 partials with .6 rolloff as an initial setting; raise to 10 or 12 partials with rolloff .75 for complex timbres like the bassoon (weak fundamental). Computation time is dependent on the number of partials sought. The maximum number is 16.

iodd (optional) -- if non-zero, employ only odd partials in the above set (e.g. inptls of 4 would employ partials 1,3,5,7). This improves the tracking of some instruments like the clarinet The default value is 0 (employ all partials).

iconfs (optional) -- number of confirmations required for the pitch tracker to jump an octave, pro-rated for fractions of an octave (i.e. the value 12 implies a semitone change needs 1 confirmation (two hits) at the spectrum generating iprd). This parameter limits spurious pitch analyses such as octave errors. A value of 0 means no confirmations required; the default value is 10.

interp (optional) -- if non-zero, interpolate each output signal (koct, kamp) between incoming wsig frames. The default value is 0 (repeat the signal values between frames).

ifprd (optional) -- if non-zero, display the internally computed spectrum of candidate fundamentals. The default value is 0 (no display).

iwtftg (optional) -- wait flag. If non-zero, hold each display until released by the user. The default value is 0 (no wait).

## Performance

At note initialization this unit creates a template of inptls harmonically related partials (odd partials, if iodd non-zero) with amplitude rolloff to the fraction irolloff per octave. At each new frame of wsig, the spectrum is cross-correlated with this template to provide an internal spectrum of candidate fundamentals (optionally displayed). A likely pitch/amp pair (koct, kamp, in decimal octave and summed idbout form) is then estimated. koct varies from the previous koct by no more than plus or minus kvar decimal octave units. It is also guaranteed to lie within the hard limit range ilo -- ihi (decimal octave low and high pitch). kvar can be dynamic, e.g. onset amp dependent. Pitch resolution uses the originating spectrum ifrqs bins/octave, with further parabolic interpolation between adjacent bins. Settings of root magnitude, ifrqs = 24, iq = 15 should capture all the inflections of interest. Between frames, the output is either repeated or interpolated at the k-rate. (See spectrum.)

## Examples

      a1,a2   ins                                                         ; read a stereo clarinet input
      krms    rms        a1, 20                                           ; find a monaural rms value
      kvar    =          0.6 + krms/8000                                  ; & use to gate the pitch variance
      wsig    spectrum   a1, .01, 7, 24, 15, 0, 3                         ; get a 7-oct spectrum, 24 bibs/oct
              specdisp   wsig, .2                                         ; display this and now estimate
      koct,ka spectrk    wsig, kvar, 7.0, 10, 9, 20,  4, .7, 1, 5, 1, .2  ; the pch and amp
      aosc    oscil      ka*ka*10, cpsoct(koct),2                         ; & generate \ new tone with these
      koct    =          (koct<7.0?7.0:koct)                           ; replace non pitch with low C
              display    koct-7.0, .25, 20                                ; & display the pitch track
              display    ka, .25, 20                                      ; plus the summed root mag
              outs       a1, aosc                                         ; output 1 original and 1 new track

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