Audio/Video Sync Issues

[ChickenKrispy]

I am having some very frustrating sync issues with a particular set of files. All audio samples are recorded at the same 48 khz. The video is recorded at 29.7 at a constant frame rate. The sequence is set to 48 khz at the appropriate 29.97 fps. Yet no matter how hard I bang my head against the wall the audio persists to desync at a constant rate. By that I mean within 3 minutes the audio is 16 frames ahead of the video. By the end of the 58 minute video the audio is completely and utterly out of sync. My mic is a Shure SM7b connected to a Focusrite Scarlet Solo. As I said all audio sources were recorded at 48 khz. What frustrates me the most is that I've been using the same recording set up for the past year and this is the first time i'm having the issue. I immediately suspected that the video footage was incorrectly reporting constant frame rate. So I tossed it into Handbrake to convert it to CFR and nothing has changed. I've triple checked my audio hardware settings on Audition as well as my export settings. The issue eludes me. Any help or thoughts would be greatly appreciated.

Sincerely,

Steven

[Jim_Simon]

I do recommend not using USB audio.  Seems to cause quite a few issues.

What recorded the video?

[ChickenKrispy]

I use a Canon Vixia HF R700. I've heard of issues with USB interfaces. However up until now I've never had an issue with this particular set up. So you suspect latency being the issue here?

[ChickenKrispy · Accepted solution]

Though I have found a work around for my issue I'd like to post my findings before closing this thread. In regards to the issue of audio dropping out, it would seem that this was a simple interface conflict with USB 3.0/3.1. As it we're USB 3.0 is not quite as backwards compatible as it has been led to believe. Plugging my Focusrite Scarlet Solo into a 2.0 slot solved that issue. Then came another sync problem. After solving the original desync dilemma I found that my audio was now slowly desyncing over time. Typically this would be caused by one source being say 48khz and another being anything other than that, say 44.1khz. Regardless of the fact that my audio in all aspects is recorded and edited in the exact same format. In regards to compression, frequency and timing. However, the issue comes into play when the time base is not being relayed properly to the video footage. By this I mean my video source time base was ever so slightly off. When I say ever so slightly I mean .01%. Adjusting the video speed to 100.01% in Premiere before editing perfectly re-aligns the sync. No more sync drift! Now I had to figure out what caused the issue. Up until now I had never had an issue. I realized that around the time this began I had muted the mic on my camera. Since I record my audio/video separately I figured why not? How naive I was. Re-enabling the mic fixed the issue and no speed correction was necessary. My thought process here is that whilst the time base remained the same, the camera had no audio to report back to and therefore it inherently drifted. Once the camera could again reference the audio during recording the issue vanished. I figured I would explain my experience and my findings so that anyone else having similar issues might find this helpful.

Thank you,

Steven

Audio:

• Shure SM7b
• Focusrite Scarlet Solo
• Cloud Lifter

Recording Software:

• Adobe Audition

PC Hardware:

• MSI X370 Gaming Pro Carbon
• AMD Ryzen 7 1800X 3.6Ghz Octa Core
• nVidia GeForce GTX 1080 ti 11GB GDDR5X VRAM
• Corsair Vengeance 32GB DDR4 3000Mhz
• Samsung 850 EVO 250GB SSD
• Western Digital Caviar Black 1TB HDD 7200RPM
• Corsair RMx Series RM750x 750W 80 Plus Gold Full Modular
• Windows 10 Pro 64 Bit

[soundlab]

If you use different devices for Audio and Video you need to clock them from the same source.

With different devices I also mean: Computer camera and soundcard (no matter if USB or not). Audio speed and video speed are almost always different in consumer and prosumer equipment. You cannot avoid this problem of drifting audio/video with consumer devices!!

That's why you have (and pay for) Genlock and Wordclock inputs on professional devices. With a professional Sync Generator (like e.g. the Rosendahl nanosyncs) you are able to force audio and video devices to the same speed. Such devices deliver a Wordclock (normally 48kHz) and a TriLevel Genlock which are inherently locked to each other. This is the only way to record long takes (>10minutes) without A/V sync drift.