Doepfer A-119 External Input/Envelope Follower - Manual (Page 3)

doepfer System A - 100
Ext. Input / Envelope Follower
A-119
3
3. The Envelope Follower: how it works
The external audio signal (see Fig. 1a) is patched into
input ! or ", depending on its level. It is amplified by
an amount set by the gain control 1, brought up to
A-100 internal operating level, and can then be output
from audio outs § and/or $.
To produce envelope and gate signals, the amplified
signal is put through a full-wave rectifier, so that the
internal signal output has only positive voltages (see
Fig. 1b).
Next, the rectified signal passes through a 50 Hz low
pass filter, and is sent to envelope output %.
H With input frequencies of less than 50 Hz,
patch the envelope output % into an A-170
slew limiter, set to a time constant of greater
than 20 ms, to avoid remnants of the signal
being audible in the envelope.
The signal at the envelope output is compa-
red with the adjustable trigger threshold (T in
Fig. 1c), to produce gate signals, available at
output &.
Fig. 1: The envelope follower: how it works
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T