[ardour-dev] Advice on FFT Analysis ... How to Read it, and What Can it Tell You?

John Rigg ardev at sound-man.co.uk
Sat Nov 4 12:21:31 PST 2006

On Sat, Nov 04, 2006 at 12:48:06PM +1100, Shayne O'Connor wrote:
> i'm gettin ready to master some tracks, so i'm trying to get used to the
> idea/purpose of FFT Analysis ... here's a composite graph of a short
> region of all my tracks from a session:
> http://s52.photobucket.com/albums/g11/machinehasnoagenda/screenshots/?action=view&current=BassGuitar.png
> ... and here's the guitar and bass alone:
> http://s52.photobucket.com/albums/g11/machinehasnoagenda/screenshots/?action=view&current=BassGuitar.png
> ... would i be right to assume that this graph is suggesting the bass
> and guitar are a bit close in frequency range and need to be eq'd to
> avoid muddiness?
> any tips on how to get the most out of the FFT Analysis would be much
> appreciated ;)

Your graph looks like the frequency scale is linear, which is fairly
useless. You need a logarithmic scale (preferably on both axes),
otherwise the low frequencies are so squashed together that you
can't see any useful information.

Mixing according to a spectrum analyzer is probably a bad idea. They can
be useful in pinpointing problems, but they fail to take into account various
characteristics of the ear. For example, the frequency response of the ear
varies according to sound level (take a look at a graph of equal-loudness
curves at different SPLs and you'll see what I mean). Trust your ears
first, analysis tools second.


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