dbx 122 - Page 32

professional system.
The two systems were designed for different applica-
tions. The bandpass filter in the signal path in the dbx II
system is slightly more restrictive, rolling off 1dB at 30Hz.
In addition, the rms detection circuitry in dbx II units is
sensitive only up to 10kHz, so high frequency losses on
the tape or transmission lines will not create encode/decode
mistracking. THE OVERALL FREQUENCY RESPONSE
OF dbx Il PROCESSING DOES COVER THE ENTIRE
AUDIBLE SPECTRUM.
dbx Type | dbx Type I!
» Due Play Response}
Fig. 20 — Comparison of dbx Type | and Type II Processing
Type | is the curve used in the 152, 154, 157 and 158 as well
as professional recording studio dbx equipment. Type I! is the
curve used in the 128, 122, 124 and 140 series, which is optimized
for such applications as broadcast and disc noise reduction, as well
as tape recording.
The dbx II system is also equipped with a TAPE/DISC
switch that introduces a further low end roll off (—3dB @
30Hz) in DISC mode. This has been provided to permit
decoding of special dbx encoded phonograph records; the
roll off protects the rms detection from mistracking due to
record warp or turntable rumble. The dbx I! system is
especially suited to noise reduction with cassette and
al
50 100 500 1K 5K 10K 20K —10 29 50100 500 1K SK 10K 20K
cartridge recorders which have limited frequency response 31
compared to a professional studio machine.
Changes in the pre-emphasis and de-emphasis curves also
distinguish the dbx professional and dbx II systems. How-
ever, both systems offer the same 30dB of broadband noise
reduction, and a 10dB improvement in headroom for tape
recordings. The signal processing differences between dbx
professional and dbx II make it inadvisable to encode with
one system and decode with the other; audible tracking
errors could occur.