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AM-10HD / Aug 2008
A M - 1 0 H D G U I
The Coupling control may be adjusted over the range of 0dB to ‑30dB.
At a setting of 0dB bands 1, 2, 4, and 5 can
never
have more gain than
band 3. Such a setting is useful in formats such as Classical and Jazz that typically
would not wish the spectral “correction” caused by the outer bands increasing their
gain but still need those bands to reduce their gains when it may be appropriate.
The setting of ‑30dB essentially turns the Coupling mechanism off — the outer
bands are then allowed to have more gain than band 3 ‑ up to 30dB more gain (which
is a lot!).
In typical programming situations the best setting of the Coupling control will
likely be somewhere between ‑3.0dB and ‑8.0dB.
If grander settings of the Coupling control (greater than about ‑10.0dB) are nec‑
essary in order for the station’s programming to sound more consistent on the air it
might be advisable to investigate the cause and correct it, because this implies either
poor frequency response in one or more parts of the signal chain or grossly poor
quality program material coming from some source.
AGC Backoff
The AGC Backoff control does two things:
1. It adjusts the processing balance between slower AGC action and faster
compression;
2. It enables the sum and difference gains to be different if program content
allows it.
With the Backoff control set at 0dB, the audio gain control is primarily due to
slower AGC action, and therefore short term program dynamics are largely unaffected
unless they exceed the AGC gain reduction by at least 1dB. In that case momentary
gain reduction by the compressor will place the gain where it needs to be to return
control to the AGC.
With the Backoff control at the other extreme, or ‑12dB, gain control is primarily
due to fast compression and short term dynamics will be aggressively controlled.
The setting of the Backoff control allows the audio compression texture to be
modified from a gentle, almost unobtrusive control (Backoff between 0dB and about
minus 2.0dB), to very obvious compression (Backoff control at ‑3.0dB or greater
negative numbers) creating a sound that is similar to vintage compressors and limit‑
ers from the 1960’s.
Note that regardless of the setting of the AGC Backoff control, the AGC and
Compressor stages operate with their algorithms linked mathematically and there is
no method for changing the relative thresholds between the AGC and compressors.
