Making Music
  Computer Music Software and Hardware

Level crossings

The secret of a good loop is to find zero-crossing points in the sample. If you use an audio editor to zoom in closely on a waveform you will see it as a wavy line that oscillates above and below a central horizontal line. When the waveform is on the horizontal line it is at zero volume and these are the places where you should cut the sample. Most audio editors have a function that automatically cuts the audio at zero-crossing points to help make seamless joins.

If you cut audio when the waveform is above or below the line the waveform will be at a certain level. If you butt this against another waveform or the start of the same waveform if you're creating a loop, unless their levels match exactly you'll hear a click or glitch. Many pieces of software have a Loop Tuner or a Loop Finder which butts the end of the sample up against its start so you can see and hear what it will be like when looped. These make loop creation so much easier.

Shape of fades to come

When making loops, it's not always enough simply to cut at zero-crossing points. You should  also look at the shape of the wave and try to pick points so that the join looks like a continuation of the waveform. So, for example, if the waveform leading to the zero-crossing point at the end of a loop sweeps up from below the line, look for the waveform in the next section to continue the curve above the line.

Also, for a seamless loop, the tone of the start and end should be similar. You won't find it easy to fade the end of a piano sample into the start of a trumpet sample. Although, having said that, there are ways to do this...

Cut tips

If you have a stubborn sample or want to loop a sample with different start and end sounds, try this. Copy a section from the start of the sample and merge it with the end. Use your editor's merge function or do it with a crossfade. This adds part of the tone from the start of the sample to the end which should make it easier to loop.

If you are creating your own samples for looping, here's another tip. Instead of recording the sample once, record it twice in succession and create the loop using the second recording. This allows any frequencies at the end of the first sample - any reverb tails, for example - to be captured at the start of the second sample so its start and end will sound more alike. It's a similar idea to the previous tip.

Creating fades and crossfades at both the recording and sample level require a little application. It's a creative part of audio editing and a technical understanding of the process will help you do a better job.

For more info... For an excellent discussion about using software curves: www.editorsguild.com/newsletter/SepOct99/tipaudio_cross.html