Topic: Digital Recording acting like tape stretch

[jkupry1@gmail.com]

I have a very unique problem.

I recorded a show using two recording devices. I took a two stereo mix out of the board into my MBOX. I also used the ZOOM H4 to capture the crowd ambience. When I import the audience feed and mix it with the MBOX signal it starts  to play in sync but as the recording continues to play it becomes out of sync. It's almost if the digital signal from the Zoom H4 has a mind of its own. It's digital technology, I cant explain it, I matched up the kick of the snare perfectly in the beginning, and it plays fine for about 30 seconds and then as the recording continues it goes out of sync even more. It's as if someone is holding their finger down on a tape to slow it down. Any ideas? Both were recorded in 44.1, 26 bit, stereo. Any help would be greatly appreciated.

[ethan]

It's pretty common to drift.  But drifting audibly after only 30 seconds seems odd. Unually it's more like 8-10 minutes.

Both your sources are WAV files right? Not VBR MP3.


Think about this. If a sample rate chip is guarenteed 99.999% accuarate. At 44100 samples per second. It doesn't take long before two clocks of the same accuracy drift by many samples.

-e

[jkupry1@gmail.com]

They were both recorded in .WAV format. Is there anyway to reset the clock to match each other? The file is a full set 60+ minutes so by the end they are way off balance.

[easy jim]

You are going to have to either stretch or shrink one of the two sources to fix the drift.  Your Mbox source is (probably) going to have a better clock than the Zoom, so you should use that source as your 'master clock' reference and manipulate the Zoom source in your audio editing software.

For more info., check out this thread where these issues were discussed in a bit more detail:
http://taperssection.com/index.php/topic,77942.0/all.html

[eric.B]

They were both recorded in .WAV format. Is there anyway to reset the clock to match each other? The file is a full set 60+ minutes so by the end they are way off balance.

not that I am aware of.. just like two digital watches cannot keep exactly the same time, neither will two crystals running sample rates in digital audio recorders..  This is where a "master clock" or having two units running off the same clock come into play..