This IS the Avid L2: Re: [Avid-L2] Re: Canon 5d shot at 23.98 with audio recorded at 48,048 syncing?

Wednesday, June 26, 2013

Re: [Avid-L2] Re: Canon 5d shot at 23.98 with audio recorded at 48,048 syncing?

QTchange ' could' help if you jump lots of hoops. Don't do it.
Get WaveAgent. Period.

But, a bit more on the theory, and to make your life more miserable than it already is:
The sample rate defines how many samples there are recorded in one second. That you already knew.
Now, if you record at 48K, and then alter the file's sample rate to 24K, you effectively tell the player (in this case, Avid) that there were just 24K samples recorded every second.
Avid will believe it of course, and play it at half speed. Same as overcranked video.
The opposite works as well of course.
Now, as Jay told you, this used to be done when sound was recorded next to 23.976 video intended to speed up to 24 for film playout,
and to make things as less as confusing as possible, as of course (same as no indication about track layout / bad file naming / never the same mic on a channel)

So far it's all easy and understandable.
Now for the fun part.
You may have trouble with timecode.
BWF does NOT have timecode. It has a time STAMP, and it is written down as ' samples after midnight'
This means, sound recorded at 48K with a timestamp of 96000 has TC 00:00:02:00
(96000 samples have passed since zero hour at the starting of this recording, 96000 samples / 48000 samples/sec = 2 sec )

Just changing the sample rate of a file will affect playspeed / duration / pitch, but it will also change the math, as the noted samples after midnight get divided by another number.
Basicly it's drop/non-drop offset. (1000/1001 time difference)

To add to the joy, there can be a secret handshake inside the BWF files to tell Avid NOT to give you any options to set params on import.
(This was a very good idea, making it this way ensured that under no circomstances there can be confusion at all, and everything will always go exactly right.)
I suspect this flag is set, otherwise you would have gotten a question from Avid on what to do with the files.

Now since i only do these kind of things when absolutely needed, i don't know exactly what you can set where in Avid, but i do know WaveAgent will let you do anything needed on your files.
At least you now know what to look for....

Bouke

VideoToolShed
van Oldenbarneveltstraat 33
6512 AS NIJMEGEN, the Netherlands
+31 24 3553311
----- Original Message -----
From: johnrobmoore
To: Avid-L2@yahoogroups.com
Sent: Wednesday, June 26, 2013 8:01 AM
Subject: [Avid-L2] Re: Canon 5d shot at 23.98 with audio recorded at 48,048 syncing?

Here's the suggestion I got offlist:

John;

Once an audio file has been recorded in the field with more samples, you need to restamp it as 47954 with an application like WaveAgent from Sound Devices (free for both OSX and Win)

Once the files have been set to 47952, Avid will try to compensate and will go back into sync for your camera originals at 23.976.

Do this on a copy of the files to make sure you got it right.

--- In Avid-L2@yahoogroups.com, John Moore <bigfish@...> wrote:
>
> I don't have all the specifics but they shot Canon 5D at 23.98 and audio sampled at 48,048Hz. Now in avid the audio drifts. I'm trying to help remotely so I don't have all the specific details but IIRC in an old meridian avid you could do audio pullup/pulldown through the analogue inputs only. I believe that has changed so files can be pulled up or down when importing audio files into an Avid project. This is not a workflow I've worked in can someone remind me if this is possible at all or if it's possible in a standard 23.98 project or does it have to be a film 23.98 project or is there even a difference these days. Most of my generic knowledge is based on information back when there was only the NTSC 24 frame project days of meridian systems.
>
> If Avid won't do the audio conversion would QT change do anything in this regard or is there a way to do an external sample rate conversion with an external program. I'm not sure what the format of the separate audio files are but I'd bet it's from one of the cheaper sound recording systems. TIA
>
> John Moore
>
> Barking Trout Productions
>
> Studio City, CA
>
> bigfish@...
>
> [Non-text portions of this message have been removed]
>

[Non-text portions of this message have been removed]