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FM-531HD / May 2013
F M - 5 3 1 H D P R O G U I
In a conventional peak detector, 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.
By increasing the sample rate of the detector to oversample the audio waveform
only at the detector it becomes possible to read the audio waveform 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 detector 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 the Enable check box is checked the look ahead limiter is enabled.
L/R Linked
When this box is checked the left and right channel control signals are common.
This prevents unnatural stereo image shifts when one channel needs to reduce the
signal to control peak excursions.
Final Limiter Drive
This control drives the output of the 31‑band limiter into the final peak limiter.
Care should be taken to monitor the FINAL meter in the analysis display to view the
amount of gain reduction in the final HD limiter. Too much gain reduction can cause
pumping.
Limiter Threshold
The Limiter Thresh control adjusts the relative threshold of the look ahead limiter
compared to the setting of the Final Limiter Drive control and is adjusted until the
onset of limiting is reached with normal program material as indicated by the gain
reduction bargraph. Adjustable over a +/‑ 6dB range.
Attack Time
The look ahead Limiter Attack Time control adjusts the attack time of the look ahead
limiter. Attack times from 0.2 milliseconds through 0.5 milliseconds allow the limiter
to “look ahead” 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 30 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 milliseconds. This is because the 0.5 millisecond look ahead is always in
Summary of Contents for FM-531 HD
Page 2: ...Technical Manual Wheatstone Corporation May 2013 FM HD Digital Audio Processor FM 531hd...
Page 122: ...page A 2 FM 531HD May 2013 A P P E N D I C E S Appendix A General Specifications A 3 Contents...
Page 128: ...page A 8 FM 531HD May 2013 A P P E N D I C E S Appendix B FM 531HD GPI Interface A 9 Contents...