Dolby Laboratories 430 - Manual (Page 19)

4-2
In situations where the interference is broadband, both the LF and HF bands can be used in varying
amounts. The two expander sections are in series therefore their effects tend to sum. For this reason, it will
be found that the amount of processing used can often be reduced when both bands are brought into play
since they broadly overlap in the band 200 Hz to 2 kHz.
20 Hz 100 Hz 1 kHz 10 kHz 20 kHz
0 VU ((((+ + + +4 4 4 4 d d d dB B B B))))
–10
–80 VU
–70
–60
–50
–40
–30
–20
For each band, there is an untreated path which is mixed with the treated path in variable amounts
determined by the position of two controls on the remote unit in such a way that, for nominal level signals,
the change from untreated path to treated path causes no audible change in level. This is useful because it
allows the sound engineer to treat the noise rather than having to juggle with the predominant signal. As
the amount of untreated signal increases, it progressively dilutes the effect of the processing without
changing thresholds, forming a natural progression from processed to linear effect.
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