Re: Detection of harmonics and rhythmic structure

[Eric Scheirer <eds@xxxxxxxxxxxxx>]

Hi Brian,

>Does anyone know some good algorithms for determining a) the presence or
>absence of harmonics in a signal (non-speech), and b) whether the signal
>is discrete or rhythmic (repetitive)?  I can imagine that these two
>questions are related, one is in the frequency domain and one in the time
>domain.  I have fooled around with autocorrelations, but want to be able
>to extract a number that would capture the amount of either harmonic or
>rhythmic structure in a signal.

With regard to (b)...

The basic technique that I reported [1] for finding the tempo and beat
of musical sounds is straightforwardly turned into a "rhythm detector."
In fact, we did exactly this and used it as one of the features in
in the speech/music discrimination system I built with Malcolm [2].
The basic idea is to divide the signal into subbands, find the
envelope in each subband, and calculate the periodicity somehow
(eg autocorrelation).

In signals that are perceived to be rhythmic,
the autocorrelations will be spiky and consistant cross-band, while
in signals that are not perceived to be rhythm, the autocorrelations
will be flat and/or different from band to band. As far as I know,
there's no formal psychoacoustic evidence of this, but we acheived
good empirical results in engineering-style tests.

>PS if you have Matlab code, all the better.


Matlab and C++ code for my rhythm-analysis system is available if
you mail me offline.  As far as I know (maybe Malcolm can say
different), the speech/music system is unfortunately not publically
available.

Hope this helps,

 -- Eric

REFERENCES

1. Scheirer, E. D. "Tempo and beat analysis of acoustic musical
signals."  J. Acoust. Soc. Am 103:1, pp. 588-601, 1998.

2. Scheirer, E. D. and Malcolm Slaney. "Construction and evaluation
of a robust multifeature speech/music discriminator."  Proc.
1997 IEEE Int. Conf. Acoust Speech Sig. Proc., pp. 1331-1334.

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