"DVFilm Maker" audio sync question at DVinfo.net

David Lach · October 19th, 2002, 11:41 AM

Hi

I just wanted to hear from Marcus and others as well that did extensive tests with this promising app in conjunction with the Panasonic DVX100 if the fact that DVFilm Maker changes the audio rate from 48 000 to 48 048 to compensate for the NTSC 1% slower rate (in the 2:3:3:2 pulldown to true 24p operation) can cause a lost of sync between the audio and the image, especially with long projects like an hour or more.

It looks fine right now testing with short samples but I'm wandering if the sound conversion is full proof against this kind of problem which would surely be catastrophic for me.

Thanks

Marcus van Bavel · October 21st, 2002, 12:07 AM

David,

The playback rate is sped up from 23.976 ( which is 24 x 29.97/30) to exactly 24 frames/sec. The new audio rate of 48048 is chosen as approximation for 48000 x 24/23.976 = 48048.048048... and so has an error of about one part per million. That is a very small error and you could playback 12 hours before the audio goes significantly out of sync.

Of course you can also select the other mode which leaves the playback rate the same.

David Lach · October 21st, 2002, 10:39 AM

Thanks for the answer Marcus.

I do need to use the true 24fps and not the 23.976fps because it is meant to be blown to film later on. (also for NTSC use but this part is very insignificant so unless it means trouble to go from 24fps to 29,976fps I think I'll stick with this value).

My projects rarely go over 2 hours so if you say that I could notice a significant lost of audio sync at about 12 hours, than my guess is that at 2 hours it won't be noticeable... Those this sounds about right ? In the worst case scenario I guess I could split the final file in half.

October 19th, 2002, 11:41 AM	#1
David Lach Major Player Join Date: Oct 2002 Location: Montreal, QC, Canada Posts: 570	"DVFilm Maker" audio sync question Hi I just wanted to hear from Marcus and others as well that did extensive tests with this promising app in conjunction with the Panasonic DVX100 if the fact that DVFilm Maker changes the audio rate from 48 000 to 48 048 to compensate for the NTSC 1% slower rate (in the 2:3:3:2 pulldown to true 24p operation) can cause a lost of sync between the audio and the image, especially with long projects like an hour or more. It looks fine right now testing with short samples but I'm wandering if the sound conversion is full proof against this kind of problem which would surely be catastrophic for me. Thanks

October 21st, 2002, 12:07 AM	#2
Marcus van Bavel Contributor Join Date: Sep 2002 Location: Austin TX Posts: 176	David, The playback rate is sped up from 23.976 ( which is 24 x 29.97/30) to exactly 24 frames/sec. The new audio rate of 48048 is chosen as approximation for 48000 x 24/23.976 = 48048.048048... and so has an error of about one part per million. That is a very small error and you could playback 12 hours before the audio goes significantly out of sync. Of course you can also select the other mode which leaves the playback rate the same.

October 21st, 2002, 10:39 AM	#3
David Lach Major Player Join Date: Oct 2002 Location: Montreal, QC, Canada Posts: 570	Thanks for the answer Marcus. I do need to use the true 24fps and not the 23.976fps because it is meant to be blown to film later on. (also for NTSC use but this part is very insignificant so unless it means trouble to go from 24fps to 29,976fps I think I'll stick with this value). My projects rarely go over 2 hours so if you say that I could notice a significant lost of audio sync at about 12 hours, than my guess is that at 2 hours it won't be noticeable... Those this sounds about right ? In the worst case scenario I guess I could split the final file in half.