beautypg.com

System a - 100, A-119, The envelope follower: how it works – Doepfer A-119 External Input/Envelope Follower User Manual

Page 3: Doepfer

background image

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

0

0

0

0

a

b

c

d

T