Sequential prophet 5 - Program Selection and Editing

Figure 2-1
Monophonic Subtractive Synthesis
Besides a dynamic envelope, a musical voice usually has a timbre which consists of a fundamental
pitch and a number of harmonics - all of varying relative strengths. Pitch and timbre synthesis raises
a distinction between two techniques, shown in figs. 2-0 and 2-7. The first additive synthesis might
create a timbre by summing the output of several sine-wave VCOs for the fundamental and each
harmonic. In contrast, subtractive synthesis can start with one sawtooth-wave VCO generating the
fundamental with extensive harmonics, then obtain the desired timbre by subtracting unwanted
harmonics with a low-pass filter.
The additive and subtractive techniques have encouraged the development of two types ot instru¬
ments. roughly, "studio", and "peformance". Since one can individually control each h f r ^°" ,c '
additive synthesis may be potentially more accurate for synthesizing a particular sound. Whether
they are additive or subtractive, studio synths may be configured from dozens of modules intercon¬
nected by "patch cords". The modules have knobs to establish the initial settings of VC-parameters
such as frequency (INIT FREQ), pulse width (PW). and resonance (RES). But the flexibility and com¬
plexity of modular synths discourages their "live" use on stage because significant sound changes
often require repatching modules and precisely checking knobs. Favorite, comp ex sounds take a
long time to create, and almost as long to recreate on a modular synth. So these often monophonic
synths instead feed multi-track recorders on which polyphonic interpretations or compositions are
actually orchestrated.
A comparison of the number of modules and interconnections depicted in figs. 2-0 and2-T shows
why the subtractive configuration has become the popular technique for performance synt s.
Obviously, subtractive synths may be far more portable and their patches will not be as elaborate.
Originally, these synths were monophonic. Or they exploited organ technology so more than one
note could be played at a time. "Preset" switches that select fixed patches supplanted many modular
controls. Though one could certainly change sounds quickly using them, many players found preset
synths unsatisfactory because they eliminated an essential part of synth musicianship. Some manu¬
facturers have offered partially-programmable instruments. But before the Prophet appeared it was
not possible for a keyboardist to instantly select his or her own customized synth sounds and play
them polyphonically.
2-3