dbx 128 - Handling Subsonics and Interference

20
HINTS TO GET THE MOST OUT OF
dbx TAPE NOISE REDUCTION
Mixing
Individual channels which have been dbx-encoded cannot
be mixed together unless they are first individually decoded.
In fact, encoded tapes must be decoded before limiting,
equalization, or any other special signal processing (except
level or gain changes).
Recording Levels
Maximum recorded levels (as displayed on your tape
machine’s VU meters) will be somewhat lower with the
128 switched to REC mode, and minimum levels will be
higher. In other words, the VU meter on the tape recorder
will nat “track’’ the VU meter (tH any) on the preamp or
mixer. This effect is due to the 2:1 compression. The
average peak readings on the tape recorder meters should
be significantly lower when recording with dbx encoding,
especially with cassette machines. This level allows plenty
of headroom for peaks without danger of tape saturation,
and it simultaneously provides adequate separation from
the tape noise.
Special Tapes
It is not necessary to increase record levels to ‘take ad-
vantage” of elevated level (High Output Low Noise) tapes.
Instead, it is desirable to retain standard record and play
levels, providing extra headroom for truly accurate transient
response. The extra few dB of recorded level are not neces-
sary because dbx processing avoids residual tape noise even
with standard tapes. We recommend the new smooth sur-
faced tapes (calendered tapes) which have inherently low
noise.
Bias, Equalization and Alignment
Hiss level in tape recording is a function of the recorded
signal level as well as bias level. In order to minimize tape
modulation noise, it is important that the tape machine be
properly biased for the particular tape used. If your tape
machine has bias and equalization switches, experiment to
find the settings that yield the lowest tape modulation noise
and the best frequency response with dbx encoding and de-
coding. Proper head alignment is also important because the
2:1 expansion of the dbx decoding can exaggerate any fre-
quency response errors in the tape record/ playback process.
In addition, always keep your tape heads clean and demag-
netized to avoid extra noise and distortion.
Effects
When recording with dbx II tape noise reduction, use
limiting and compression for special effects only. The dbx
encoding process makes routine limiting and compression
completely unnecessary. (As stated in the hint ‘Mixing’, any
such signal processing would be before encoding, if at all.)
Microphones and Pickups
When making live recordings from microphones or instru-
ment pickups, the signal level must first be preamplified
before being applied to the 128’s RECORD INPUT jacks.
\f your tape machine has mic preamplifiers, these cannot be
used because they would bypass the dbx encoding. A low
noise preamplifier should be used to take full advantage of
the noise reduced recordings. Some stereo receivers have mic
preamps, and there are relatively inexpensive battery powered
mic preamps, too.
Coughs, shoe scuffs, and similar sounds which may never
have been audible in conventional recordings can become an
annoyance when captured on a quiet dbx recording, so the
ambient room noise should be held to an absolute minimum.