dbx 122 - Page 37

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Pre-Emphasis and De-Emphasis
Tape modulation noise is a phenomenon that occurs
with all tape recordings. It consists of noise sidebands which
appear on either side of the signal which is being recorded,
and it is caused by inherent characteristics of the tape.
Modulation noise levels are significantly higher than the
residual background noise of the tape, although the modula-
tion noise falls off as the frequency moves away from the
recorded signal. The signal masks modulation noise com-
ponents that fie nearby in frequency, but it does not mask
noise which is several octaves above. For this reason, modu-
lation noise is most often a problem when a strong, low
frequency signal is recorded. (What might be heard, for
example, is a low organ or bass guitar note that is accom-
panied by a rushing, hissing sound .. . as the note dies,
so does the noise). dbx applies pre-emphasis and de-emphasis
to reduce modulation noise by up to 12dB (Figure 22 —
2 & 2A).
Levels
When using linear compression and expansion there is
no threshold at which the compression and expansion takes
place. Therefore no pilot tones or routine calibration are
required. The 122 and 124 are provided with REC LEVEL
MATCH controls, and PLAY LEVEL MATCH controls.
These controls adjust the dbx record and play gain to
correspond to the nominal levels of your equipment.
These level adjustments let you maintain the same levels
in record, play and bypass modes for monitoring con-
venience. Level matching is not essential for proper encode/
decode tracking. (Refer to Page 15 for level adjustment
information.)