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AM-10HD / Aug 2008
A M - 1 0 H D G U I
By increasing the sample rate of the detector (right graphic) to oversample the
audio waveform only at the detector it becomes possible to read the audio wave‑
form with much higher precision. This results in far more accurate peak control.
Note that it is not only unnecessary to oversample the main audio path, it is
actually undesirable; it would result in the same problem a conventional detec‑
tor has because the ratio of audio to detector sample rates would be the same as
in the conventional case. Additional DSP resources would have been used with
no benefit.
Limiter Enable
When this checkbox is checked the
lookahead limiter is enabled.
L/R Linked
When this box is checked the left and
right channel
gain control
signals are com‑
mon. This prevents unnatural stereo image
shifts when one channel needs to reduce
the signal to control peak excursions and
the other does not.
Limiter Thresh
Adjusts the relative threshold of the lookahead limiter compared to the setting
of the Lim/Clip Drive control and is adjusted until the onset of limiting is reached
with normal program material as indicated by the HD gain reduction bargraph.
Adjustable over a +/‑6dB range.
Attack
Adjusts the attack time of the lookahead limiter. Attack times from
0.2 milliseconds through 0.5 milliseconds allow the limiter to “lookahead” in time
and react to signal peaks before they arrive at the limiter’s gain control algorithm.
Attack time settings greater than 0.5 milliseconds and up to the limit of
100 milliseconds allow the limiter to operate conventionally. For example, if the
attack time control is set to 1.0 milliseconds, the actual attack time is 0.5 mil‑
liseconds. This is because the 0.5 millisecond lookahead is always in circuit and
its value must be subtracted from any adjustment of 0.5 milliseconds or greater
in order to know the actual attack time.
Release
Controls the primary (fast) release time of the lookahead limiter. Slower set‑
tings (longer release times) cause the peak limiter to recover more slowly from
limiting. Release times set too slow may allow undesirable signal ducking to
occur. Fast release times increase signal density, and release times that are too
fast result in increased intermodulation distortion which can “muddy” the sound.
The control ranges from 33.0 to 330.0 milliseconds.
