over three decades ago on analog
machines far less sophisticated than
what you can build yourself today.
If this all sounds exciting to you,
then let’s tuck in and see how to learn
about analog music synthesizers.
THE THREE ASPEC TS
■ FIGURE 1. Three parameters of sound.
The emphasis here is on learning
about analog music synthesizers. Not
only are their circuits perhaps more
accessible to beginners, but they’re
also imbued with a certain warmth of
sound that is unequaled. And lest you
think analog technology is too feeble
to be useful in this digital day and age,
keep in mind that some amazing
music, like Walter Carlos’ famous
Switched On Bach, was created
Analog music synthesizers depend
upon the rather simple concept that
any sound (musical or otherwise) can
be described by three parameters only:
frequency, amplitude, and harmonic
content. The basic notion is that if
we can analyze a sound into its three
constituents, then by reversing the
steps we should be able to synthesize
it from scratch, as well. Let’s look at
these three aspects in more detail.
Frequency is a measure of how
often a waveform repeats in a given
interval. Refer to Figure 1. Comparing
the waveform in Part (a) with the reference waveform, we see that it is twice
the frequency. In loose terms, the frequency of an audio signal corresponds
to what a musician calls pitch. For the
two triangle waves illustrated, the
second one is an octave higher (twice
the frequency) than the reference.
The second parameter of sound is
that of amplitude. Again, refer to Figure
1. Here we note that the height of the
waveform in Part (b) is about
half that of the reference waveform.
If this were an audio signal we were
listening to, we’d say that the sound is
softer or less loud. Notice in this case
that the frequencies of the reference
waveform and Part (b) are identical; it’s
only the amplitudes which differ.
Finally, the third aspect of sound
can be referred to as harmonic
content. An easy way to understand
this is by trying a simple experiment.
Sing the following vowel sounds in
one long, drawn out phrase, “ooooh ...
ahhhh ... eeeee.” Slur the sounds
together, but don’t alter the pitch or
volume at which you sing them. Even
though you’ve held two of the parameters fixed, something is obviously
changing. This is the harmonic
content, called timbre by musicians.
Electronically, it corresponds to
an oscillator generating different wave
shapes or perhaps a filter modifying
those shapes somehow. Refer one
final time to Figure 1 and notice how
the signal in Part (c) has the same
frequency and amplitude as the reference, but the shape is clearly different.
By the way, an oscillator that puts out
a triangle wave will sound rather pure
and flute-like compared to the raspier,
violin-like timbre of a ramp wave.
If we can come up with the means
to manipulate the frequency, amplitude, and harmonic content of an
electronic waveform, then in theory we
should be able to synthesize just about
any sound we desire. A traditional
musical instrument is pretty much
stuck in a rut; its ability to change all
three parameters is somewhat limited
in scope. But with a synthesizer, many
more combinations are possible
including those never before heard!
WHAT’S INSIDE AN
While the fundamental concept is
quite simple, coming up with a complete circuit to usefully manipulate all
three parameters of sound can be
daunting. The only reasonable way to
proceed is by divide and conquer. That
is, rather than thinking of a synthesizer
■ FIGURE 2. Block diagram of a typical single voice analog synthesizer arrangement.