Digital Sound & Music: Concepts, Applications, & Science, Chapter 6, last updated 6/25/2013
Once you have all your samples recorded, you need to edit them and add all the metadata
required by the sampler. In order for the sampler to do what it needs to do with the audio files,
the files need to be in an uncompressed file format. Usually this is WAV or AIF format. Some
samplers have a limit on the sampling rate they can work with. Make sure you convert the
samples to the rate required by the sampler before you try to use them.
The first bit of metadata you need to add to each sample is a loop start and loop end
marker. Because you’re working with prerecorded sounds, the sound doesn't necessarily keep
playing just because you’re still holding the key down on the keyboard. You could just record
your samples so they hold on for a long time, but that would use up an
unnecessary amount of RAM. Instead, you can tell the sampler to play the file
from the beginning and stop playing the file when the key on the keyboard is
released. If the key is still down when the sampler reaches the end of the file,
the sampler can start playing a small portion of the sample over and over in an
endless loop until the note is released. The challenge here is finding a portion of
the sample that loops naturally without any clicks or other swells in amplitude
or harmonics.
Figure 6.37 shows a loop defined in a sample editing program. On the
left side of the screen you can see the overall waveform of the sample, in this
case a violin. In the time ruler above the waveform you can see a green bar labeled Sustaining
Loop. This is the portion of the sample that is looped. On the right side of the screen you can see
a close up view of the loop point. The left half of the wave is the end of the sample, and the right
part of the wave is the start of the loop point. The trick here is to line up the loop points so the
two parts intersect with the zero amplitude cross point. This way you avoid any clicks or pops
that might be introduced when the sampler starts looping the playback.
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