dbx 128 - dbx II Tape Noise Reduction; Expansion and Compression Explained

be to raise the overall program level, allowing the louder
sounds to become even louder. However, when the pro-
gram’s loudest sounds are too high in level, they cause
distortion. Thus, the difference between the noise level
and the maximum undistorted level of a tape machine, disc,
or radio broadcast is not wide enough to accommodate the
full dynamic range of a live performance.
To get around the inherent dynamic range limitations in
a given medium, the original program is often ‘‘compressed.”’
This means that its dynamic range is restricted by making
the loud passages quieter and/or the quiet passages louder.
Compression thus avoids the dynamic range limitations of
the medium by reducing the dynamics of the program.
Compression is effective, but unfortunately it also removes
the program’s excitement and realism. Given the necessity
for compression, engineers long ago realized that if there
were some way to reverse the process, restoring the
dynamic range of the compressed program,the quality of
recorded music could be significantly improved. Until
recently, this ‘reverse compression” process, known as
“expansion,” had not been successfully applied in any
consumer product.
dbx has developed techniques that make a dramatic
improvement in the dynamic range of any recorded musical
material: (a) the patented dbx II Tape Noise Reduction
System for tape machines and phonograph discs, and
(b) the linear decibel compression/expansion system. The
dbx 128 incorporates both of these systems which may be
used independently or in combination with each other.
You can use the 128’s dynamic range enhancer to reduce
the noise of records or FM broadcasts, or you can capture
all of the widest range program material on your conven-
tional cassette or reel-to-reel tape recorder using dbx II
tape noise reduction.
dbx Il Tape Noise Reduction
dbx 11 tape noise reduction circuits ‘‘encode”’ a program
before it is recorded on a tape recorder and “‘decode” it
upon playback. This process reduces tape noise to inaudi-
bility and retains the original program’s dynamic range.
This means that a recorded program will not have any more
audible noise than the original source. Also, the dbx-
encoded program will retain the dynamics and excitement
of the original source without causing tape saturation.
When to Use the dbx I! Tape Noise Reduction System
Use the 128’s dbx tape noise reduction circuitry to
avoid
audible
tape
noise
and
increase
headroom
when
you
record a tape of a live performance, dub (copy) a con-
ventional disc onto a tape, or record any other source,
such as an FM broadcast.
The 128’s tape noise reduction circuits can also be used
to
decode
a
dbx-encoded
phonograph
disc.
dbx
encoded
discs have been recorded with dbx I! noise reduction
processing, and already have all the advantages of dbx
noise reduction.
dbx tape noise reduction processing cannot reduce noise
on an existing tape if it ha’ been recorded without dbx
encoding. Similarly, the dbx tape noise reduction circuits
cannot reduce noise on conventional phonograph records.
However, the dbx 128’s expander circuits can reduce
these types of noise, as explained in the next paragraph.
dbx Expansion and Compression
For the most part, noise in an FM broadcast or ona
phonograph disc is only audible when the program levels
are quiet. dbx linear decibel expansion increases the
program dynamics so the loud levels become fouder and
the quiet levels, inciuding the noise, become quieter.
Simultaneously, expansion restores much of the dynamic