[music-dsp] [on topic] diplaying a frequency spectrum

jeffmcc at ihug.co.nz jeffmcc at ihug.co.nz
Tue Sep 4 21:06:15 EDT 2001


Hi All,

I have been working on a Spectrum Analyser.  It has a choice of either linear 
or log frequency scale.  I am using a simple FFT based approach. But when in 
‘log’ mode I stretch the horizontal scale to show even spacing per octave.  I 
thought this would be correct until I read….

> If you
>look at pink noise on an "RTA" analyzer, which groups in bands of constant
>fractions of an octave, it will look "flat" -- on the same analyzer, white
>noise appears to rise at 3dB/octave.  However, on an FFT type spectrum
>analyzer, which groups in 'bins' which are all the same number of Hertz in
>bandwidth, the white noise appears "flat", while the pink noise appears to
>fall at 3dB/octave.

So…. If I subtracted 3db per octave from my FFT results, would that be 
sufficient to make my display accurate, or is it more complicated than that???

Any insight appreciated.

Jeff M



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