Oberheim OB 12, Руководство по эксплуатации

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OB 12 Z-Domain Synthesizer
8. 4 EDIT FILTERS
173
containing the following parameters:
•
OSCILLATOR1
([ENV DEPTH] assigned to OSC.1)
: regulates the depth of the envelope, or the
amount by which the pitch of the signal generated by the first oscillator will vary over time, in
a range of values of +50 (maximum envelope, i.e. maximum pitch variation), 0 (no envelope,
i.e. pitch variation zero) and –50 (maximum negative envelope).
•
OSCILLATOR2
([ENV DEPTH] assigned to OSC.2)
: regulates the depth of the envelope, or the
amount by which the pitch of the signal generated by the second oscillator will vary over time,
in a range of values of +50 (maximum envelope, i.e. maximum pitch variation), 0 (no envelope,
i.e. pitch variation zero) and –50 (maximum negative envelope).
As we have seen in section 5, which explains how sound is generated, the OB-12 emulates the
subtractive synthesis technique for sound generation. With this type of synthesis, the timbre is
created starting from a waveform with a high harmonic content (in our case, the sum of the signal
produced by the two oscillators, the Ring Modulator, white noise and the modulations of the
various signals) which is then filtered to eliminate or attenuate the superfluous and/or unwanted
harmonics.
The name “subtractive synthesis” therefore derives from the fact that harmonics are subtracted
by a filter.
Analog synthesizers used normally to use VCFs ( Voltage Controlled Filters), with voltage control
used to vary the cut-off frequency. This allowed real-time control from a panel, and above all by
an envelope generator.
In modern synthesizers VCFs have been supplanted by DCFs (
Digitally Controlled Filters), which
not only guarantee immunity from noise, but also offer unlimited flexibility of use. DCFs are produced
in software version with DSPs (Digital Signal Processors).
Let us see, for example, how a square waveform is modified by the action of the filter in the
various mode and cut-off frequency configurations:
Naturally, the above diagrams are only an example of the waveform leaving the filter, since as we
have seen, the waveforms generated by the two oscillators are much more complex.