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Topics in this section include:
Limiters
Overview
Limiters prevent clipping by attenuating
signals that exceed a set threshold. The
amount of attenuation is de
fi
ned by the
ratio of the limiter and expressed as two
numbers.
The time it takes for limiting to begin
once signal has exceeded the threshold
is referred to as the attack time, and
the time it takes for limiting to cease
once signal has fallen back below the
threshold is referred to as release time.
Sound Devices recommends using limiters at all times. Without input limiters,
high signal conditions can overload a channel and cause distortion. In normal
operation, with a properly set gain structure, the threshold of the input limiter is
rarely reached. The default threshold of all limiters on the 688 is 16 dBu.
All 688 limiters use a 20:1 compression ratio. This means that any signal that
exceeds the threshold by 20 dB will exit the limiting stage at only 1 dB above
the threshold. The 688 limiters have a 1 ms attack time and a 500 ms release
time.
The input limiter is actively limiting when the respective input’s Input Activity
LED illuminates yellow. Limiting activity will also be displayed as a yellow square
on the right side of the input’s meter on the Main screen. If the limiting activity
is regularly indicated, reduce the amount of gain applied to the channel by turn-
ing down the Trim control.
Enabling the Limiters
When enabled, the limiters are globally activated at either a Hard Knee or Soft
Knee setting. The knee of the limiter determines how the limiter operates in
relation to the set threshold. With hard knee, when the signal reaches the
threshold, the mixer immediately attenuates only those peaks above the
threshold, compressing at whatever ratio is set. With soft knee, attenuation
begins slightly before the threshold—at about 6 dB—for a more gradual, tape-
like sound, making the compression much more dif
fi
cult to detect.
Overview
Enabling the Limiters
Adjusting the Threshold
Linking Limiters
