Grass Valley AMX-3981 2014 - Manual (Page 69)

GUIDE TO INSTALLATION AND OPERATION
AMX-3981 | 63
to be applied. The new preset should only be applied then, so that the processing change is applied only to the new
audio type.
Each card preset may contain hundreds of parameters: some are used to configure input parameters and others
output parameters. Unfortunately, all changes are applied more or less at one time, so some compromise is often
required when processing delays through the card are relatively long, such as in Dolby Digital and Dolby Digital Plus
encoding applications. Understanding what processing changes are required, and where those changes are applied in
the signal path through the AMX-3981, will help in making the most effective choice of delay time.
Most of the time, the different presets are nearly identical and only a few parameters will change from one preset to
another. Obviously, if the preset needs to control input and output parameters at the same time, it will be impossible to
select a perfect Delay.
Application for the Automatic Preset Recall:
Figure 5.60 shows the application. When DV is present on
embedded input channels 7-8, it is passed to the output. When
not present, a downmix version of the main 5.1 will be used. It
has been determined by the customer that the audio level on the
DV channels is always above -72 dBFS because of the noise
floor. If it goes below that threshold, we can assume there is no
audio present.
User Preset 1 will be recalled when DV is present on the
embedded audio input channels 7-8. The embedded audio
output shuffler for channels 7-8 will be programmed to pass the
input channels 7-8.
User Preset 2 will be recalled when DV is silent on the
embedded audio input channels 7-8. The embedded audio
output shuffler for channels 7-8 will be programmed to pass the
output downmix channels 15-16 made from channels 1-6.
The No Signal Duration will be set to 30 msec and the Threshold
to -72 dBFS. Assuming the total processing delay of the AMX-
3981 is set to 66 msec to give enough reaction time between the
detection of the silence and the application of the preset, the
Automatic Preset Recall should be configured as shown in the
picture below:
The delay to apply the preset has been optimized to take into account the No signal Duration, the total
processing delay of the card and the internal reaction times of the card. Determining the accurate preset
Delay to apply is rather complicated. Please contact our Technical Support department if you experience any
difficulties.
Figure 5.60 Application for automatic
preset recall