Oberheim OB 12 Operating Manual - page 32
OB 12
Z-Domain Synthesizer
7.
4 MODIFYNG the TIMBRE (FILTERS)
152
As we have mentioned when discussing the synthesis technique used by the OB-12, the signal
generated by the oscillators is rich in harmonics, or in other words it has a very wide frequency
content. The filter can be used to attenuate specific harmonics, or a given range of frequencies,
in order to obtain the desired sound (with regard to the timbre quality).
In fact, the OB-12 FILTER section uses two filters which can be set up exactly as required with
regard to type, cut-off frequency and their interconnection.
The filter control section is the following:
•
[FREQUENCY]: regulates the filter cut-off frequency. Turning the trimmer anti-clockwise
increases the cut-off frequency. Depending on the type of filter, the significance of the cut-off
frequency varies: refer to the description of the [FILTER 1] button with regard to operation of
the filters in relation to the cut-off frequency.
•
[KBD TRACK]
(Keyboard Tracking)
: you can use this
trimmer to vary the behaviour of the filter in relation
to which key is pressed on the keyboard.
Intermediate values will keep the trigger frequency
the same throughout the keyboard range. This
means that higher notes will have a softer sound
than lower notes, with fewer partials. Turning the
trimmer completely to the right will increase the
harmonics in the higher notes, so that they are
brighter while the lower notes are darker. Conversely,
if the trimmer is turned completely to the left the
higher notes will have even fewer harmonics than
in the standard setup (trimmer in central position).
The lower notes will therefore be brighter, and the
higher notes darker.
•
[RESONANCE]: regulates the resonance coefficient. As the diagram shows, the resonance
causes an enhancement of the frequencies close to the cut-off frequency value. Increasing
the resonance will give greater selectivity in establishing the frequencies affected by the
enhancement.