Frequency Space Editing with Adobe Audition

Turn Your Editing Machete into a Frequency-Selective Scalpel

By Craig Anderton

Adobe Audition, and its predecessor Cool Edit Pro, have always had stellar noise reduction tools. But Frequency Space Editing (FSE), an editing option that became available starting with Audition V1.5, is impressive not just for its ability to eliminate noise problems with pinpoint precision, but to allow selective editing on very specific parts of a sound.

Do you have a drum loop that you really like except for a wimpy kick drum? Isolate just the kick, and run it through a bit of distortion to beef it up...or eliminate a single triangle hit in the middle of a song. And about the guy who coughed in the middle of your sensitive acoustic guitar moment on that live recording: With a little luck, you can nuke the cough and leave the guitar intact.

Although other programs have been able to isolate a band of frequencies over a specific time range and manipulate them, Audition's tools are the most cost-effective implementation yet. But be aware that while the results can seem miraculous, they can't solve every problem.

For example, with one drum loop I wanted to get rid of an annoying clave hit, but it it had been put through a ton of reverb. Although it was possible to eliminate the main clave sound, removing the reverb meant taking out a lot of frequencies that needed to be kept. On the other hand, I played on a record many years ago where the drummer hit the hi-hat late coming out of a solo, and it always bugged me. With FSE, I was finally able to cut just the hi-hat from the stereo mix, and place it where it belonged. Now that's pretty amazing.

HERE'S LOOKING AT YOU

Using FSE requires a different look at audio. Instead of the usual waveform display that shows amplitude over time, FSE uses a spectral display that shows distribution of energy in specific frequencies over time. You can access Audition's Spectral view from the View menu.

My one complaint about this view is that the vertical axis (frequency) uses a linear scale rather than a logarithmic one, so all the lower frequencies (where most of the interesting musical sounds lie) are squeezed into the display's lowest part. The workaround is to right-click on the vertical calibration, then select Zoom In so you can focus in on a specific frequency range. For example, if you want to remove a low-frequency sound, zoom in to frequencies below 400-500Hz. However, remember that you'll also need to zoom out to see a wider range of frequencies if you want to remove a sound's transient components, which are generally higher in frequency.

KILLING A KICK

Here's a real-world example of how to remove the kick drum from a funk-type drum loop (I wanted to substitute a tougher, more electronic sound). The following diagram shows the steps you would take to do this; following are descriptions for each step.

Here are the main places on the screen to do Frequency Space Editing.

1. Go View > Spectral View. The Spectral view replaces the default Waveform view. Increased energy in a specific range is brighter, while decreased energy is darker.
2. Select the Marquee tool (the square with the dotted border).
3. You'll probably need to use the Zoom tools, both on the vertical and horizontal axis, to make it easier to identify the area you want to process. Be patient; it takes practice to learn to recognize the various "sonic signatures" of different sounds.
4. There are a few zoom shortcuts for the vertical axis. One is to right-click on the vertical calibrations, then choose Zoom In or Zoom Out. You can also do this with keyboard equivalents (Alt = and Alt - respectively). Or, right-click on the calibrations, and drag over the area to which you want to zoom.
5. Here, the marquee (bordered in white for clarity) has selected the kick drum. Note that when you select in one channel, the other channel defaults to selecting the same area as well. The clue that this is the kick is the high-amplitude burst of energy in the bass range (the higher-frequency bursts to the left and right are the snare). While you're learning to recognize which frequencies are essential to a sound, you can always isolate, cut, then audition (and if it doesn't work, undo) to make sure you've found the right area to edit.
6. Now that you've isolated the area you want to cut, go Edit > Cut. This removes the area defined by the marquee.
7. For the smoothest possible removal, go Favorites > Repair Transient. Providing the area you selected is relatively small, this will "morph" audio over the cut, which is the audio equivalent of putting a flesh-colored band-aid over a cut so you don't see it.
   
   

SO YOU THINK YOU'RE DONE...

Well, not quite; in this case, there's a transient at the beginning of the kick that also requires removal. Let's describe the process for removing the entire kick, using four "frames" of a sort of "how-to comic strip."

A marquee (shown surrounded with a white border for clarity) selects the main kick drum hit. The object here is to define the kick drum's "body" so it can be removed.

Deleting the kick produces the spectral view in this frame. However, note that the kick's attack transient remains.

A marquee is drawn around the kick's attack transient (again bordered in white for clarity).

Deleting the transient produces the final result. Note how the kick drum is completely gone – it's as if it had never existed.

Dealing with signals that include a lot of harmonics is correspondingly more complex. Fortunately, though, these harmonics tend to be fairly thin "slices" that you can remove without altering the rest of the signal.

The top half of the above diagram shows a triangle hit's harmonics (each one is bordered in white). The bottom half shows what happens after they've been deleted (note the black spaces) and gone through the transient repair process. On playback, you hear no triangle at all.

SO WHAT'S THE CATCH?

This technique's "jaw drop factor" depends on what you're trying to process. With a dry, fairly simple drum loop, you can remove individual drums and never even know they were there. On the other hand, as alluded to earlier, if there's reverb it's almost impossible to remove a specific sound because the reverb extends the sound's duration and the amount of bandwidth it takes up.

Also, if you're trying to delete a sound with lots of harmonics, remember that the more of the spectrum you remove, the more likely this will affect the sound of other instruments. In the example given above of removing a triangle hit, I had to be very careful to remove the minimum amount of signal possible. Otherwise, other sounds with high frequencies (high hats, cymbals) were affected. This is why it's important to zoom in and remove no more than is absolutely necessary.

So much for cautions, here's something very cool you also need to remember: You can apply any editing operation to a frequency space, not just cut or delete. It one particularly tedious example, I had a song where only the open hi-hat was too loud all the way through the song. I isolated each open hi-hat hit, and reduced the level for each one by 4dB. Miraculously, the open hi-hat fell right into the mix, and because it was being attenuated rather than completely eliminated, there were no ill effects on the rest of the tune. Another one of my favorites is adding a bit of processing from PSP's Vintage Warmer to kick drums and toms...yum.

Frequency Space Editing is pretty amazing. If you have Adobe Audition 1.5 or higher and haven't checked out this feature, you're missing out on a tool of exceptional potential.

Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.