On Wed, 17 May 2006 20:28:31 +0200, Jonas Wulff <[EMAIL PROTECTED]> wrote:
On Wed, 2006-05-17 at 19:46 +0800, Graham Evans wrote:
This is kind of a general question; however:
I am thinking of buying a flash-card audio recorder for various reasons
- possibly a Marantz pmd 671.
I want to make sure it will work well in any future video work. The
device doesn't have a time-stamp capability but I can't see why a
digitally recorded audio track would go out of time once initially aligned.
...
I think there can be problems resulting in non-perfect sampling rates...
I once recorded something with two soundcards to have 4-channel input,
but the audio tracks were about half a second out-of-sync after some
minutes of recording.
This is a general problem with aligning recordings made with separate
devices with inaccurate clocks or imprecise sample rates. It is quite
common that DV cameras don't record exaclty 48000 sound samples per second,
but 48005, for example.
Some professional equipment can use an external high quality clock to
remain perfectly in synch for hours. With semi-professional and amateur
equipment you do not have much options but looking for clear cues and the
beginning and the end, align your recording at those, and find out if the
recordings have a different number of samples between those points.
If the recordings slip noticeably relative to each other, you have to
resample the worst offenders, so that they get the right length.
Don't know if this happens with cinelerra, though..
This can happen no matter what software you use. Hardware problem.
Cinelerra has a convenient feature: You can change the source material's
sample rate, to get it played back at the correct speed. Cinelerra will
resample all audio tracks whose sample rate differs from the "Format"
sample rate used in the rendering.
--
Herman Robak
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