Forums

Constant Q spectrogram Vs FFT Spectrogram?

Started by Simon March 1, 2006
I am a newcomer to Spectrogram analysis.
 It is said, there are two kind of spectrogram, one is constant Q
spectrogram(octave band filter,logrithm of frequency ).The other is FFT
spectrogram.  I knew a little about FFT spectrogram.But I am not so
sure what's the difference between them?
advanced Thanks

Simon

Simon wrote:
> I am a newcomer to Spectrogram analysis. > It is said, there are two kind of spectrogram, one is constant Q > spectrogram(octave band filter,logrithm of frequency ).The other is FFT > spectrogram. I knew a little about FFT spectrogram.But I am not so > sure what's the difference between them?
I think one major difference is in the appearance of overtones or harmonics produced by some fundamental frequency phenomena. For a constant-Q display, the overtone series spacing gets closer and closer with the harmonic number, but the pattern of spacings stays the same for different fundamental frequencies. This might be good for pattern matching an unknown pitch against the known spectra of some given musical instrument, voice or vowel, etc. In a linear frequency FFT display, the spacing between overtones is about the same, but the spacings all get equally wider if the fundamental pitch goes up. So the pattern of overtones has a different visual size depending on fundamental frequency or pitch. It's easier to reconstruct the original signal from a complete set of FFT data, not sure about constant-Q. IMHO. YMMV. -- rhn A.T nicholson d.0.t C-o-M