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AM-10HD / Aug 2008
A M - 1 0 H D G U I
Lim/Clip (Limiter/Clipper) Drive
This control adjusts the drive level into the HD lookahead peak limiter or clipper
(if used – we do not recommend clipping used ahead of a codec!). The drive level
is adjustable over a +12/-18dB range. The resolution of the control is 0.05dB, fine
enough for the most exacting limiter drive level adjustments.
Higher HD Limiter drive settings cause the output audio to become denser and
at extreme settings processing activity may become quite obvious. We recommend
using only enough Limiter Drive to achieve 3-5dB of limiting on signal peaks as this
will mitigate processing artifacts that would detract from the otherwise pristine sound
of the HD signal path.
The HD output is peak controlled by a special high-speed feed forward limiter
with a 0.5 millisecond lookahead time. The control path, and not the audio path, is
oversampled in order to achieve extremely precise peak control. Because the goal of
oversampling is better peak control through finer definition of the audio waveform,
oversampling of the audio signal itself is not only unnecessary, but wastes DSP re-
sources.
The graphics below visually illustrate why control signal oversampling is more
effective.
In a conventional peak detector (left graphic), audio excursions occurring between
individual samples are “missed,” and therefore the audio signal is “under-read” during
this instant. This results in inaccurate peak control.
