Aural Exciter Circuit Description - Aphex COMPELLOR 300 Operating Manual

6.2 AURAL EXCITER Circuit Description
AURAL EXCITER processing is introduced between the COMPELLOR VCA
output and the output level control, as shown in Fig. 6-3. Thus, ideal condi-
tions for processing are maintained with minimum signal path complexity
for highest performance.
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Fig. 6-3. Block diagram of COMPELLOR Model 303 circuits.
6.2.1 Filter Circuit
AURAL EXCITER processing begins at pin 3 of H401, where audio from the
COMPELLOR 1001 VCAtt is passed to an adjustable second order high-pass
filter consisting of U402B, U403B, and associated components. This filter
determines the lower frequency limit of AURAL EXCITER enhancement.
Dual potentiometer VR402 tunes the cutoff frequency from approximately
1.2 kHz to 6 kHz. The filter damping (or "Peaking") is adjusted by VR403,
which effectively tunes the "Q" of the circuit between about 0.7 and 1.1, thus
contouring the cutoff response between a gradual slope and a slightly
peaked but sharper cutoff. The gain of the filter is set at unity.
6-8 Circuit Description