Owner`s manual

CHAPTER 3 -
15
CHAPTER 3 -
The Craft of audio Synthesis
3.2.2.2.2
Enharmonic Series
Enharmonic, in this context, means
“not forming a harmonic series.”
Some waveforms do not repeat
themselves at a regular interval;
the spectra of such waves will have
components at strange non-integral
frequency ratios, or they may have
shifting spectral components that die
out and reappear. Some percussion
instruments, such as kettledrums,
or bells, have enharmonic spectral
components.
In audio synthesis, you can use various
modulation techniques – such as AM
and FM - to generate enharmonic spectra.
3.2.3
Attributes of Random Signals
A completely random signal – noise – actually has a
continuous
spectrum: it does not
consist of isolated sines in a harmonic series, nor even in an enharmonic series. A noise
spectrum is a continuum of frequency components; in order to describe it, we have to
talk about how much energy is in each band in this continuum. One kind of noise may
have high-frequency energy, and another has low-frequency energy.
In audio synthesis, noise is an extraordinarily useful signal. Filters can be used to shape a
noise spectrum into almost anything – even pitched sounds.
3.2.3.1
Spectral Balance (Color)
The physical processes (such as molecular motion or random popping of electrons from
one atom to another) that we typically depend on for random electronic noise have a
frequency distribution of equal probability at any frequency, or through any frequency
interval. Curiously enough, this produces noise signals that, for audio purposes, don’t
sound properly balanced across our range of hearing. They sound too bright.
Not all spectra are harmonic. An Arbitrary collection of
sines at unrelated frequencies is "unharmonic".
Increasing Power
Increasin
g
Pitch
ANY
etc.
+1.7
1.47
2.43
2.725
3.157