Patch B04.sampler.pd (Figure 2.14) shows
how to use a wavetable as a sampler. In this case the index into
the sample (the wavetable) is controlled by mousing on a number box
at top. A convenient scaling for the number box is hundredths of a
second; to convert to samples (as the input of
tabread4~ requires) we multiply by 44100 samples/sec
times 0.01 sec to get 441 samples per unit, before applying
pack and line~ in much the same way as
they were used in the previous example. The transposition you hear
depends on how quickly you mouse up and down. This example has
introduced one new object class:
: simple high-pass (low-cut) filter. The creation
argument gives the rolloff frequency in cycles per second. We use
it here to eliminate the constant (zero-frequency) output when the
input sits in a single sample (whenever you aren't actively
changing the wavetable reading location with the mouse.) Filters
are discussed in chapter 8.
The pack and line~ in this example are
not merely to make the sound more continuous, but are essential to
making the sound intelligible at all. If the index into the
wavetable lookup simply changed every time the mouse moved a pixel
(say, twenty to fifty times a second) the overwhelming majority of
samples would get the same index as the previous sample (the other
44000+ samples, not counting the ones where the mouse moved.) So
the speed of precession would almost always be zero. Instead of
changing transpositions, you would hear 20 to 50 cycles-per-second
grit. (Try it to find out what that sounds like!)
