Crystal Vision
Introduction
SYNNER-E 3G User Manual R1.2
8
10/09/2012
Tracking audio delay
When enabled, the built-in video tracking (strictly speaking Audio Follow Video tracking)
helps to ensure that the audio delay matches the video delay to maintain lipsync; by operating
dynamically in Synchronisation mode as input/output timing changes.
When video tracking is on in Synchronisation mode, the rate at which the audio delay tracks
fast or abrupt changes in video delay is controlled by the tracking audio delay (TAD) rate.
The faster the TAD speed, the faster the audio delay will match the video delay, but at the
expense of musical pitch.
Since the TAD speed can be audible as a pitch change the response time needs to be chosen
with care. A sports event may well benefit from a fast TAD speed but classical music with
piano and violins would require the slowest speed.
For example a TAD speed of 0.1% can cause a pitch change of the same value to be heard as
the audio delay catches up with the video.
To put this in perspective, imagine a piano recital is in progress and a concert pitch A above
middle C is heard. This has a fundamental frequency of 440Hz. A 0.1% change would
produce 440.44Hz. A sharp or B flat is 466.16Hz so in this case the audio delay slew rate only
causes a pitch change of the order of one sixtieth of a semitone.
The TAD speeds are 0.8%, 0.4%, 0.2%, 0.1% and 0.05%.
TAD versus slew rate
A 40ms change in video timing only takes five seconds at the 0.8% TAD speed. Each
decreasing response step takes double the time to catch up, so a 0.05% rate means that the
audio would take 80 seconds to catch up with the video.
The following table relates audio tracking response time to video changes for a range of TAD
values:
Video timing
change
T.A.D.
0.05%
T.A.D.
0.1%
T.A.D.
0.2%
T.A.D.
0.4%
T.A.D.
0.8%
40ms
80
seconds
40
seconds
20
seconds
10
seconds
5
seconds
20ms
40
seconds
20
seconds
10
seconds
5
seconds
2.5
seconds
10ms
20
seconds
10
seconds
5
seconds
2.5
seconds
1.25
seconds
5ms
10
seconds
5
seconds
2.5
seconds
1.25
seconds
0.6
seconds
1ms
5
seconds
2.5
seconds
1.25
seconds
0.6
seconds
0.3
seconds
