Loop and Groove Audio Editing

You may not be as "locked in" to a loop's sound as you thought you were

by Craig Anderton

Yes, loops are convenient because you can use them “out of the box.” But why be normal? Or for that matter, put up with a loop that’s close to what you want, but not perfect? There are quite a few tricks you can use with loops to make them groovier, courtesy of digital audio editing . . . so let’s start.

SELECTIVE REMOVAL 

A common DJ technique to take parts out of a mix—for example, remove the kick when it’s time to chill out the feel a bit, or take out the low-level percussion when you need a sparser, lighter sound. Of course, you can’t do that with a complete loop—or can you? 

To remove a kick, use your digital audio editor to cut the bass response using a highpass filter with a very steep slope (e.g., 48dB/octave; see Fig. 1). If you don’t have any filter with a steep enough slope to remove the kick, or at least minimize it, try using a low-frequency shelf (a 100Hz corner frequency makes a good starting point). Apply the EQ process several times to steepen the slope, or alternately, insert several EQs in series (Fig. 1). Repeat as necessary until you’ve marginalized the kick. 

Fig. 1: Inserting several EQs with shallow slopes in series can make for a much steeper slope.

Another removal technique involves using a noise gate to remove low-level signals. This can also “tighten” and “sharpen” a loop, as only the percussive peaks remain. You can apply this to the loop, or perhaps better yet, use a noise gate plug-in for real-time processing where you vary the noise gate threshold in real time. 

An even more interesting option is available courtesy of Adobe Audition’s Frequency Space Editing option or Roland's R-Mix software. Either of these lets you cut or process specific slices of frequencies at specific levels; you can even do things like surgically remove a kick drum from a loop (Fig. 2). Really.

Fig. 2: Roland's R-Mix allows processing specific portions of the frequency spectrum. In this screen shot, the kick drum range has been isolated inside the red frame, and is about to be removed.

In fact, here are two audio examples that show what you can do. The first one is a loop with the kick intact, the second has the kick removed.

BEAT EMPHASIS 

For one tune I’d found a loop that was perfect—except for an overly busy kick, as I needed more of a slammin,’ “four-on-the-floor” vibe. The solution was remarkably simple: boost the bass region on every beat. Boosting about the first 25\% of the beat (in other words, the same duration as a 16th note falling on the beat) seemed about right. This emphasized the kick when it fell exactly on the beat, but didn’t affect the other kick hits, as they simply receded a bit more into the background. 

You can even use this technique to “synthesize” the feel of a kick drum in loops that don’t have one. For example, I had a conga loop that would have been ideal for a break, but it lacked a kick. Mixing a kick into the loop didn’t sound right—I needed more contrast between the “break” and what had come before, and the kick created a sort of sameness. So, I just boosted the bass frequencies on each beat. This added a cool bass “thump” that kept the beat going, without actually sounding like a kick.  

This technique isn’t just restricted to bass frequencies; you can use something similar when you want to emphasize beats 2 and 4. But this time, boost the upper midrange a bit (at around 1 - 4kHz, depending on the application) to boost instruments like snare. Again, emphasizing the first 25\% of the beat seems to work best. 

However, be careful not to boost too much—often 2 or 3dB of emphasis is all that’s needed. Second, if you do boost, this could create distortion unless you drop the overall level prior to boosting.

KEEPING IT CLEAN

With any kind of boosting, though, make sure the region you boost begins and ends on a zero crossing. If you’re not familiar with the concept, a waveform typically crosses over a point of zero amplitude (the zero crossing point) as it transitions from negative to positive, or vice-versa. When splicing waveforms together, or processing specific regions, the region boundaries should fall on zero crossings. Otherwise, there may be an abrupt level change that causes a pop or click. While splicing or processing on zero crossing boundaries won’t guarantee a click-free signal, failing to do so virtually guarantees you’ll hear some kind of artifact.

Although it’s sometimes possible to zoom way in and use a pencil tool or equivalent to “draw out” clicks that result from processing—especially if you have a lot of time on your hands, and significant amounts of patience— a click removal algorithm intended for de-clicking vinyl can often do the job better and faster. It’s difficult to give general guidelines, because different types of de-clicking algorithms work very differently. The best approach is to experiment (make liberal use of the undo command!) until the click disappears.

WHY BE NORMAL?

Sure, you can just use canned loops. But why not put your own stamp on it? Try some of these techniques, and your music won’t sound like everyone else’s.

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.