Doepfer A-112 Sampler/Wavetable Oscillator - Manual (Page 19)

doepfer System A - 100 Sampler A-112
19
The control voltage range 0...+5V corresponds to the
256 tables (0V = table no. 1, +5V = table no. 256). To
move from one table to the next one a voltage diffe-
rence of about 0.02 V (5V/256) is required.
Example: To sweep with an LFO (Triangle output)
through 64 tables starting with table no. 96 (i.e. pas-
sing through the tables 64...128) the following conditi-
ons are required: An offset voltage of 96*5V/256 =
1.875V and an attenuation of the LFO signal to 64*5V/
256 = 1.25V (peak-to-peak). Using a A-129/3 the offset
voltage is adjusted with the offset control and the LFO
level with the attenuator control.
If each of the 64 tables are to be used - i.e. none of the
tables is to be skipped - there is a maximum frequency
that the controlling signal (LFO) must not exceed. If the
sampling frequency is 32kHz each wavetable (256
byte) takes 8 milliseconds. All 64 tables take 512
milliseconds. This corresponds to 1.95 Hz LFO fre-
quency. Consequently the frequency of the LFO must
be about 2 Hz or less to play each table without
skipping. This sounds very mathematical and theoreti-
cal but it is a good idea to understand these facts as
some unforeseen things may happen if one ignores
these details. In practice of course the resulting sound
is all that counts.
Sequencer-controlled wavetable playback
In the patch in fig. 6 the Analog/Trigger Sequencer
A-155 controls the playback of different wavetables
(step 1, 4, 5 and 7).
The sawtooth output of the LFO, patched via offset
generator A-129/3 generates the control voltage to
sweep through the wavetables. This voltage is added
to the sequencer voltage (post out 2). Thus different
ranges of the wavetable memory are used for each
step (displayed by different sound symbols). Regar-
ding offset, attenuation and LFO frequency, see the
notes on the previous page.
The sequencer control voltage Post Out 1 is used to
control the decay of an VC-ADSR, i.e. for different
decay times for each step.
Instead of an LFO an ADSR or VC-ADSR may be
used. The attack control is used in this case to adjust
the speed of sweep (decay, sustain and release con-
trol = 0).