I've done a few things with two recorders and assembled them into a
single mix in editing. As Dan says, there is drift. I had about a 45
minute concert which drifted by an un-usuable amount from beginning to
end. Here's how I fixed it:
I began by measuring the difference in time from a sharp transient near
the start of the recording to another transient another near the end. I
then used this ratio and calculated a small sample rate conversion,
followed by a header change. (for instance, convert one file from 44.1k
to 44.087 kHz, then do a header change (not a sample rate conversion)
back to 44.1 (this makes it play back at an ever-so-slightly higher
pitch that before). At that point, the two 45 minute stereo files were
really, really close in length, almost no drift. I tried time aligning
the front and rear, but ended up liking the sound of the rear channel
about 15 milliseconds behind the front, so as Dan points out, a bit of
drift when you've got a big offset is not going to break anything.
Rudy
On Jan 5, 2005, at 4:09 AM, wrote:
>>
>> Multi-track using multiple recorders. Something I have considered
>> before, but always dismissed. I may need to reconsider...
>
> Of course they drift, about one foot (sound travel time) per minute
> is typical. But if the rear pair is fifteen to forty feet away from
> the front pair, that won't matter. As Rich Peet said, effectively
> decorrelated.
>
> -Dan Dugan
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