How to fix audio sync drift

Like many of you on smaller productions, I sometime use a standalone audio recorder (Tascam DR100mkII) that has no sync input. On long takes, this audio begins to drift relative to the audio on camera.

Thanks to another person on the forum a handy free tool from Sound Devices called Wave Agent.

www.sounddevices.com/products/accessories/software/wave-agent

It allows you to add a video frame rate to an audio file, which fixes this particular issue. It's also a fast and handy way to split interleaved stereo files into individual mono files - useful for when I duplicate a single mic across two channels with different gain settings for safety.

Hope that helps someone!

" this audio begins to drift relative to the audio on camera."

This is caused by the audio recorder and video recorder being set to two different sample rates for the audio. Set them both to the same sample rate when you record, and you won't have drift issues.

But it is good to know there's a tool to save the day when that happens!

I have one question, why would you duplicate the same mic across more than one channel?

In fact the devices are set to the same sample rate of 48kHz. The issue is that there is a tiny discrepancy in the clocking of each device and as they are not synced directly, any file longer than about 10 minutes becomes noticeably out of sync - by a frame or two. Stamping a frame rate on the audio file cures that particular problem - although I'm sure mis-matched sample rates also cause issues.

The reason to use the same mic across two channels is that you can set a different analog gain on each channel, allowing for greater headroom in case of unexpected loud dialogue or noise which might clip the recording. A simple Y XLR splitter cable makes this possible. I believe some audio recorders have this functionality internally. Kind of the equivalent of dual ISO on the Panasonic Varicams