Sample-based Synthesis - Multisampling

Multisampling

A sample-based synthesizer's ability to reproduce the nuances of natural instruments is determined primarily by its library of sampled sounds. In the earlier days of sample-based synthesis, computer memory was expensive and samples had to be as short and as few as possible. This was achieved by looping a part of the sample (often a single wave), and then using a volume envelope curve to make the sound fade away. An amplifying stage would translate key velocity into gain so that harder playing would translate into louder playback. In some cases key velocity also modulates the attack time of the instrument, leading to a faster attack for loud passages.

As memory became cheaper, it became possible to use multisampling; instead of a single recording of an instrument being played back faster or slower to reproduce other pitches, the original instrument could be sampled at regular intervals to cover regions of several adjacent notes (called "splits") or for every note. This provides a more natural progression from the lower to the higher registers; lower notes don't sound dull, and higher notes don't sound unnaturally bright. It is also possible to sample the same note at several different levels of intensity, reflecting the fact that both volume and timbre change with playing style. For instance, when sampling a piano, 3 samples per key can be made; soft, medium and with force. Every possible volume in between can be made by amplifying and blending the samples.

For sample-based models of instruments like the Rhodes piano, this multisampling is very important. The timbre of the Rhodes changes drastically from left to right on the keyboard, and it varies greatly depending on the force with which the key is struck. The lower registers "bark", while the higher range has a more bell-like sound. The bark will be more distinct if the keys are struck with force. For the model to be sufficiently expressive, it is therefore necessary that multisamples be made across both pitch and force of playing.