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Unlocked Audio
Most professional videographers are now sending us digital
tapes. Occasionally we will receive a tape where the audio
drop-outs during the computer rendered transitions. Most of
these drop-outs are caused by unlocked audio. While your DV
deck or camera might play back the audio without any problems,
the Sony DSR-2000 decks have a low tolerance for switching
between locked and unlocked audio. Here is a brief explanation
of locked and unlocked audio and how you may be able to avoid
ever having a problem.
Locked audio is best described as audio done correctly, where
the relationship of audio and video are precise in the respect
that they have the exact number of audio samples to coincide
with the number of video frames.
Due to the expense of precise audio clocks, consumer DV format
cameras and some NLE systems have been manufactured allowing
unlocked audio as a cost saving measure. The result of unlocked
audio is the audio sampling running variably ahead or behind
the video frame but maintaining synchronization over the video
as a whole.
When editing with a DV based NLE when you create an edit
(transition, fade, etc.) between two different DV data streams
using unlocked audio, or even locked audio, there is a potential
for problems. During playback in a digital audio system of
an unlocked audio source or an edited transition like described
above, you may experience audio 'drop-outs' or other similar
anomalies. At HomeMovie.Com we experience most unlocked audio
issues from our customers who shoot and edit on a DV based
system then dub their video to DV-Cam. While the customers
DV-Cam VTR may seem to play the video and audio without error,
our Sony DSR-2000 machines have little to no tolerance for
these types of problems. The result is continuous loss of
audio or audio dropouts. On a positive note, there is a way
to prevent these problems. Here are a few recommendations
for converting unlocked audio to locked audio.
Here are some useful audio tips:
- Use analog audio connections when dubbing your DV tape
to DV-Cam or DVC-Pro. By eliminating the Firewire or digital
connection, you will never have unlocked audio issues.
- Transfer your video to a NLE that will output locked audio.
- Dub the DV tape from a high end DV-Cam or DVC-Pro VTR
to another using AES/EBU or serial digital audio options.
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