Grass Valley Imagestore 750 v.3.0.1 - Manual (Page 162)

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Advanced Audio
Audio Delays
Audio Delays
Dolby decoding and encoding takes time to perform. It is very important that the audio and
video delays through the Imagestore 750 are consistent and unchanging to avoid lip-sync issues
or “jumps” in transmission. This section addresses how you can achieve that.
See Dolby Processing Times on page 117,
Dolby Delays
This table lists the audio delay incurred for various Dolby decode/encode use cases, The delay is
expressed in video frames:
See Video Frame Delays on page 43 for a list of the different video frame delays that are avail-
able to compensate for any audio delays incurred by Dolby processing, such as for the use cases
listed above.
The following table shows the program delays required for the Dolby use cases above:
When an Imagestore 750 is configured to use its DVE, the DVE delays the video by 1 or 2 frames.
In this case, a compensating delay must be inserted into the background video path, post AB
mixer: A ‘PGM post A/B-mix’ delays must be applied to PGM video
7
to compensate for the extra
video delay that will be incurred when processing DVE:
Interlaced video standards 1 frame.
Progressive video standards 2 frames.
Decode Encode Dolby Delay (Frames)
— Dolby E 1
— Dolby Digital 6
Dolby E — 1
Dolby E Dolby E 2 = (1 + 1)
Dolby E Dolby Digital 7 = (1 + 6)
Table 6-8: Delay for Dolby decode/encode
Decode Encode
PGM Audio Delay PGM Video Delay—No DVE
Dolby PCM Post A/B-Mix Output
— Dolby E 1 — — 1
— Dolby Digital 6 — — 6
Dolby E — 1 — — 1
Dolby E Dolby E 2 — — 2
Dolby E Dolby Digital 7 — — 7
Table 6-9: Video delays for Dolby delay compensation
7. A post-A/B mix delay must also be applied to preview bus video if DVE preview is required.