Slow audio playback in Sound Forge

imaginACTION_films wrote on 12/2/2015, 4:47 PM
I routinely open a copy of Vegas audio tracks in Sound Forge to do my audio tweaking. Been doing it for more than a decade with no issues at all. Very simple workflow.
As of recently the audio file opens in SF 10 or SF 11 and plays back very slowly. The saved file also plays back slowly when returned to Vegas.
Advice from SCS was to check that sample rates and bit depth are the same in SF, Vegas and on my sound card (M-Audio Delta). They are all set at 48kHz 16-bit.

Puzzling and frustrating issue. Anyone got any clues on this one?
Thanks
David

Comments

imaginACTION_films wrote on 12/2/2015, 9:46 PM
It gets weirder.

I have camera files on my Vegas timeline (.mts from Canon XA10, 25 fps). They play perfectly in Vaegas. If I open them from Vegas in Sound Forge they play slowly. BUT – I have also rendered the project out as an HD AVC MP4. If I open that from Vegas into Sound Forge it plays back perfectly. Head scratching stuff...
David
Former user wrote on 12/2/2015, 10:17 PM
What audio codec is being used in the files? Is it the same in both?
Are the audio tracks of the original video files at 48k?
rraud wrote on 12/3/2015, 8:42 AM
Have you opened the file directly in SF? What's the result? The same?
If the pitch drops as well as the speed, I would surmise the audio is playing back @ 44.1kHz.. when the actual audio file is 48k. Why.. I don't know.
larry-peter wrote on 12/3/2015, 10:24 AM
I wonder if it could be that the Canon audio is PCM in AVCHD and the MP4 you're rendering for SF contains the more common (to AVCHD) ac3 compressed audio. Could SF be doing something to the file when opening because it's expecting a compressed format?

Check the original .mts file's audio properties in MediaInfo, then check the properties of the file when opened in SF and see if there are differences. I'd also check the properties of the file rendered out of Sound Forge to determine at which point the file properties are being altered.
rraud wrote on 12/3/2015, 11:51 AM
Addendum: Confirm that your Vegas audio properties are set to 48kHz.
imaginACTION_films wrote on 12/6/2015, 4:22 PM
Had feedback from Sony and also useful comments on the Sony forum.
Done a lot more testing to try and sort this out. It’s not solved but I have a workaround. Firstly, all options are set to 48kHz 16-0bit 25 fps in Vegas and SF.

If I open the MTS camera file directly in Sound Forge I get perfect playback. The problem is something to do with opening from the Vegas timeline (which has never been an issue for years!).

After lots of tests, it seems as follows:
The original MTS file has two channels (one radio mic, one shotgun).
If I open that file via Vegas (or directly into SF) playback is normal (two channels visible in SF). I normally duplicate the audio channel tracks then select Radio in one of them and Shotgun in the other.

If I select the Left channel only in Vegas, then open that in SF, I get the low, slow playback.

Once back in Vegas, I now have two takes, with just the left selected, but BOTH channels play back at once, including both normal and low, slow. THIS IS REALLY WEIRD. If I delete all takes but the original, playback is once again normal.

CONCLUSION: My workaround will be to open the two-track original either directly in SF or via Vegas. That will give normal playback. To do eg noise reduction or EQ on either track, I will have to select just that one (eg the radio mic track) in SF and work on it. More complex than it should be but at least it works.

FINALLY, on advice from the Auscamonline team, I'm going to try ingesting the original camera file via the Sony app (rather than just copying via Explorer) and see if that solves the issue. Will post results later today.
David
imaginACTION_films wrote on 12/6/2015, 6:39 PM
Imported MTS file via IMPORT>MEDIA in Vegas. Two channels play perfectly in Vegas.
Open from timeline into Sound Forge = Perfect playback.

BUT
Select Left or Right channel only.
Open from timeline into Sound Forge = Low and Slow.

All properties set to 48kHz 16-bit 25 fps in camera, Vegas and Sound Forge.
Still puzzling.
David
imaginACTION_films wrote on 12/7/2015, 6:38 PM
Ongoing discussion with SCS. Have uploaded a sample MTS file today.
imaginACTION_films wrote on 12/9/2015, 6:16 PM
Here is the very useful advice from SCS:

The reason why those symptoms are occurring is because the file being opened in Vegas still being effectively a stereo file (which you are only using one channel of) is at twice the sample rate of an actual mono file (due to the mono file only having one channel).

I recommend opening the stereo track on the Vegas timeline in Sound Forge, turning it into a mono file in Sound Forge, then re-importing that file from into Vegas after saving it out of Sound Forge. This will yield the end result of a mono file with a single wave at the correct sample rate (rather than at half sample rate).