On 10 Mar 2017, at 22:56, John Heiser jpheiser@gmail.com [Avid-L2] <Avid-L2@yahoogroups.com> wrote:some audio guy with good ears but so-so system skills can record good sound with crappy or mismatched or different frame rate or no time code.
BWF (Wave) files DO NOT have TIMECODE, but a TIME STAMP.
Audio DOES NOT have a 'framerate' identical to video / film.
To clarify:
Audio has a sample rate. In our world, most of the time 48000.
So, if audio has a framerate, it would be 48000, NOT 23.976 / 24 / 25 nor 29.97!
And that makes sense. Like film (or progressive video) is shot at X frames per second, audio is recorded at X samples per second.
Now, the 'timecode' for audio is based on an 'audio frame', and it's not written as hours/minutes/seconds/samples (audio frames), but as a simple counter.
Now since there are 48000 'audio frames' per second, the 'audio TC' in a BWF file that corresponds TC 00:00:02:00 is written as 96000
(Sample 96000 for 2 seconds.)
Again, this is exactly the same as a frame number in video, except the audio frame rate is kinda high.
No matter how an audio recorder is set-up, this number will always be as described.
BUT:
A decent audio recorder has LTC in / out, and that can be configured to output at a film or video framerate.
And, that setting will also be included in the BWF metadata.
Now, to get from the BWF timestamp to TC (that is way easier for humans to read / understand) is simple math.
And there problems might occur if you don't understand the math.
NTSC (29.97) and 23.976 are bastard formats. The frame counter in TC counts up to 30 / 24, while the speed is not 30 or 24, but 0.1% less.
That means that the BWF timestamp converted to TC gives a different number depending on what you tell the application to interpret the files.
But, no matter what it displays, with a bit of math you should ALWAYS be able to do some math and get problems fixed.
This is not always simple (Unless your name is Bouke and you love math like this.)
Since this is an Avid list:
On importing BWF files, Avid often asks you how to interpret the files. But not always. A BWF file 'might' have a flag inside telling MC NOT to ask this question, but to interpret the timestamp in a pre-defined way, that might be wrong.
Luckily there are a lot of tools out there that can alter this kind of metadata.
WaveAgent (Free from Sound Devices) is a must have for any editor who works with BWF files.
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Posted by: Bouke <bouke@editb.nl>
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this is the Avid-L2
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