About Looping

Many samplers have a looping capability. Wikipedia says: 'Samples may also have loop points that indicate where a repeated section of the sample starts and ends. This allows a relatively short sample to play endlessly.' If this seems strange, you may want to read Wikipedia's summaries of sample-based synthesis:

sample-based synthesis
the sampler as a musical instrument

One of the things that Wikipedia doesn't tell you is that it is hard to find good loop points in most sounds because it is necessary to match up the start and end points almost perfectly. Poor looping can be heard as tiny (or not-so-tiny) clicks that occur whenever the sound jumps from one endpoint to another. In the TransFormSynth, looping is made easier by a simple trick that is possible because the noise portion of the sample is processed separately from the tonal portion.

Observe that clicks (and many other looping artifacts) occur as a transient phenomenon. When the sound is decomposed into "signal" and "noise" most of these transient artifacts will be segmented into the noise path. The trick is this: whenever the input sound jumps from one loop point to another (i.e., from the end of the loop back to the start) the noise path is momentarily multiplied by zero. This does cause some disturbance to the noise path, but it is very quick (i.e., it lasts only one FFT frame) and so is hard to hear. On the other hand, it tends to remove the artifacts associated with poor looping. Try it youself. Pick one of the looped samples and change the loop start or end point by a few milliseconds. In a traditional sampler, this would be devastating to the sound. Here, it often doesn't make much difference. Of course, this does not mean that anything goes: it is still necessary to choose loop start and end points so that the sound is more-or-less the same in tonal quality and amplitude at both ends.

This trick also makes looping for rhythmic effects easier, though it is still necessary to have the length correspond to the correct duration. In this regard, it may also be useful to change the time base parameter since this will change the duration without changing the pitch or tonal quality (very much).