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.

If you understand what the purple/orange/pink stuff is, you're in great shape so far at understanding FFT.
If you understand what the purple/orange/pink stuff is, you’re in great shape so far at understanding FFT.

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.

FFT Tut Application
These spokes allow narrow bands of the spectrum to pass through – they are at very specific frequencies which match the frequencies of several notes (and selected octaves) which make up a C Major Triad (C, G, and E).

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 eighth octaves. You can use this creatively to selectively allow only narrow or wide ranges of spectra to pass to the listener. This is an EXCELLENT tool for anyone who is attempting to implement music theory into their game design. For example, one could filter away a percentage of the frequencies pertaining to the fifth of a root note in a given chord in order to make an uncomfortable, hollow interval. It would be generally extremely useful to have a frequency chart and conversion to piano notes such as the one that you can find here (or simply google search!).  It’s also useful in emulating certain frequency response patterns. For example, the built-in “Telephone – Receiver” preset and “Underwater – Deep” both sound really good with only minor tweaking. Some great effects can definitely be achieved with only a minimal amount of effort.

And speaking of results…Let’s hear em!

This is what the waveform looks and sounds like, with no additional processing.

FFT results

As you can see from the image, it still retains the intensity of the given frequencies that have been let through the filter – and thus, the same character – but the sound is now something new and wholly unique – something that reminded me of a “select” button from some old school games. Once again, like my post about tweaking samples, we might not always have access to top of the line synths or may not  always want organic sounds. This is just another tool to use to create something really cool for yourself.

Happy Editing!
-Chris