Audio Loops by Marc Schonbrun
An audio loop is any piece of digital audio that has been recorded and edited to facilitate looping without any additional help. Audio loops can be of any instrument, at any tempo and in any key. Looping relies on rhythmic accuracy in order to loop correctly. Figure 7-2 is a great example of an audio loop.
What makes the loop in Figure 7-2 so perfect? It's actually pretty hard to see in the picture, so here's a bit of help. Each vertical spike is a hard drum hit. The harder the hit, the louder the sound. Each spike is equally spread out, which shows a steady tempo. The end of the loop fits perfectly with the beginning of the loop to make it loop perfectly. A good loop has very little activity in the end of the loop; usually it's just decaying sound.
Figure 7-2: A perfect audio loop
Limitations of Audio Loops
Digital audio has some limitations. One of the biggest limitations is its inability to radically stretch the tempo and key of an audio loop without degradation. One of the mainstays of ACID and GarageBand (among others) is how the loops automatically conform to the key and tempo of your music when you drag and drop them. If the loop is 110 beats per minute (BPM) and your song is at 120 BPM, the loop will be stretched through a process call time stretching, so it conforms to exactly 120 BPM. This small 9 percent change will sound pretty transparent to the listener. But, if the loop had to be stretched more, the listener would likely hear some sonic degradation.
It's hard to explain on paper, but you'll know it when you hear it. If your loops suddenly sound odd, check out their original tempos. Too much of a stretch won't sound good. The same holds true for key changes. With more and more loops carrying melodic and harmonic information, loop programs have gotten smarter and allow loops to conform not only to tempo changes, but also to key changes, with the same limitations.
If you change the key of your loop too far up or down, it will start to sound funny! You can usually move a loop a third in either direction before experiencing any issues.
One of the other issues with audio loops is that you can't easily edit the audio. You basically get what you get. While it is possible to change the timing of an audio drum loop using Pro Tools’ Elastic Time (a method for changing the timing of individual beats in an audio loop), it isn't available for every single DAW. For most home studio users, an audio loop is a pretty closed thing.
In your DAW, see if you have a Loop Browser like those in Logic and GarageBand. These browsers are searchable for keywords, tempo, and key, so you can find the best loop easily. And many of them include data filters, so you can narrow down your searches.
