Adobe Audition

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Quick effects with the FFT filter!

Here’s something cool to try next time you’re working on something and want to create some interesting ¬†filler sounds. For you Adobe Audition boys and girls there’s a really rarely-understood tool in the Effects menu under “Filter and EQ” – the FFT filter. It’s an interesting thing, and I haven’t QUITE figured out what it exactly is. So far as I’ve dug up, FFT stands for Fast Fourier Transform, which is “an algorithm to compute the discrete ¬†Fourier transform and it’s inverse…[it] converts time (or space) to frequency and vice versa” (Wikipedia). There is a pretty involved pdf on the Fundamentals of FFT here (Rational Acoustics). If it goes over your head, don’t worry too much. The point is that it’s an analysis technique that allows you to view the sonic makeup of an audio signal. Reading the spectrum , at least in Audition, is quite simple. Open your sound file and click the Spectrum Analysis button at the top of the window to open it up. You should get a split view with the waveform on top and the spectrum analyzer on the bottom. The image makes most sense reading it in tandem with the waveform: Left-to-Right is forward in time, Bottom-to-Top is lowest pitch to highest pitch. A region of black indicates no frequency content at that location (pitch) in that time. Bright yellow indicates regions of maximum frequency content. For example, I have opened a file that tapers off pretty quickly. If you were just looking at the waveform, you might wonder why you still hear reverb for so long after the waveform is so quiet – even nonexistent – in the last bits of the audio. So you can see that the end of the clip, there is no substantial audio content above 7,000 hertz at the end of it. That same 7kHz band is a region of maximum content at the beginning of the clip during the initial clicking of the clasp. You can hear the clip in question here on soundcloud which came from the General-6000 Sound Library. Anyway, let’s get to the FFT filter. Now that you know how to read a spectrum analysis, you can imagine that an FFT filter filters parts of the spectrum. The really awesome part of the FFT filter is that it allows you to slice up and cut out trouble spots from your mix out. If you notice a sharp line shooting across the spectrum, you can use this to tame it. Cutting -90dB at 60hz on a super-fine band (and a few octaves 240, 480, 960, etc…) kills the 60hz ground humOn a more artistic level, you can chop up stuff as you want. One of the built in presets that comes with Audition is “C Major Triad” – which, as the name implies, filters out everything except parts of the spectra that fall into the C Major triad (the specific notes are a series of C’s, G’s, and E’s spanning from the second to the […]