Sound Modelling
99
wavetable sampling
synthesis
sustain
loop
splits
dynamic levels
/2
/2
/2
F
s
F
s
f
-F
0
X(f)
F
b
b
s
-F
F
s
F
s
F
s
F
s
3F
s
3F
s
3F
s
3/2 F
s
-F
0
F
b
b
s
-F
f
-F
0
F
b
b
s
-F
X'(f)
Y'(f)
-F
0
F
b
b
s
-F
f
f
Y(f)
Figure 7: Example of re-sampling with L/M = 3/2
the characteristics of the lowpass filter have to be made pitch-dependent. Alter-
natively, a set of filters can be designed to accomodate all possible pitches, and
the appropriate coefficient set is selected at run time [55].
5.2.3
Wavetable sampling synthesis
The wavetable sampling synthesis is the extension of the wavetable oscillator to
· Non-sinusoidal waveforms;
· Wavetables storing several periods.
Usually, this kind of sound synthesis is based on the following tricks:
· The attack transient is reproduced "faithfully" by straight sampling;
· A selection of periods of the central part of the sound (sustain) is stored
in a buffer and cyclically read (loop). The increment is selected in order
to produce the desired pitch;
is divided into segments of contiguous notes (splits). Each
split uses transpositions of the same sample;
· Different dynamic levels are obtained by
Sampling at different dynamic levels and obtaining the intermediate
samples by interpolation, or
4
The keyboard metaphor is used very often even for sound timbres that do not come from
keyboard instruments.