Audio drift and external sound cards

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Audio drift and external sound cards

Permanent link to this post Posted by benuski » Tue Oct 17, 2017 3:23 pm

Hi all,

I record a podcast on Zencastr with two other guys. When we download the tracks from Zencastr, one of the other hosts always has a significant audio drift. It can't be fixed with the Change Speed effect because the drift gets larger as the episode progresses, so I've been adding silences in throughout the episode to match him back up. He has a Samsung Meteor USB microphone, and I was wondering if getting an external sound card with a USB input might help. If you don't think it would, do you all have any other suggestions about what may fix it? Does he just need a new microphone?

Thanks!
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Re: Audio drift and external sound cards

Permanent link to this post Posted by cyrano » Tue Oct 17, 2017 7:29 pm

There are two solutions to the problem:

- use a centralised clock. Not feasible in this setting.

- make only short recordings. A couple of minutes at most. One song.

When dealing with long recordings, drift will always be a problem. And it gets worse with less quality gear. But even when using professional gear, you'll encounter the problem with some combinations. That's why big, professional setups like film sets use a central clock.

No central clock is why so many time is spent on post editing, when doing it professionally. Lining up audio/video is a chore.
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Re: Audio drift and external sound cards

Permanent link to this post Posted by kozikowski » Tue Oct 17, 2017 11:57 pm

However.

You should be able to make one "percent" correction no matter how long the show is.

A "normal" error has the sample rate always .003 percent (for example) fast or slow. If you can get the segment's both ends to match and the middle is significantly out of sync, that's broken.

The place your voice becomes digitized is the problem. If you have an analog microphone plugged into a digitizer, the digitizer may be off. If you have a USB Microphone, then that's the ballgame for the microphone.

Did I hit the symptom right? Both ends but not the middle? That's really super unusual.

Koz
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Re: Audio drift and external sound cards

Permanent link to this post Posted by kozikowski » Wed Oct 18, 2017 12:16 am

Do post back how this goes. This is one of the techniques we recommend for performers rather than trying to record a Skype transmission. Having sync problems is dead normal. Having moving ones is not.

Koz
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Re: Audio drift and external sound cards

Permanent link to this post Posted by kozikowski » Wed Oct 18, 2017 2:45 am

If you can track the error, there is a desperation method. Have the performer turn everything on an hour ahead and just go make coffee. If it is bad electronic parts, they will have stopped warming up and changing by the time you get to record the show.

If Sync is still moving during the production, then you got serious troubles.

Just because there's no condition a good engineer can't make a lot worse: it may not be the microphone. It's very likely it's not the microphone.

Most home recording systems depend on the USB connection to do all the heavy lifting (power the tiny lights, capture the voice, convert to digital). If the computer's USB system is ratty or bad, no microphone is going to work.

Koz
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Re: Audio drift and external sound cards

Permanent link to this post Posted by cyrano » Wed Oct 18, 2017 11:00 am

@koz

Have you had a look at what Zencastr promises?

https://zencastr.com/

Automatic post?

I mean, if they don't even time stamp their recordings...

Or maybe they do?
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Re: Audio drift and external sound cards

Permanent link to this post Posted by benuski » Wed Oct 18, 2017 1:39 pm

The USB system is not something I had considered, but that makes a lot of sense. What it looks like is happening is every time he stops talking, another error is introduced. It works fine when he is talking, but when there is silence the drift starts happening again. I have tried to use the "Change Speed" effect to sync up the ends, but then the middle and the beginning don't line up.

I will have him plug his mic into a different USB port to start and see if that affects anything. It could also be a Zencastr issue, since I have seen other people online have similar issues with audio drift.
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Re: Audio drift and external sound cards

Permanent link to this post Posted by kozikowski » Wed Oct 18, 2017 3:36 pm

It works fine when he is talking, but when there is silence the drift starts happening again.

Now you're into digital magic. We're starting to get posts from people whose digital bitstreams periodically shut down, we assume to save battery, when the system thinks there's an idle time. They get seriously damaged recordings.

No. Effect > Change Speed isn't going to do a thing for you.

I haven't been to see Zencaster yet, but it's suspicious that only one performer has problems. Describe their setup. Computer type?

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Re: Audio drift and external sound cards

Permanent link to this post Posted by kozikowski » Wed Oct 18, 2017 5:40 pm

OK, so everybody calls into Zencaster and they ship you sound files. Good idea.

I have an action item. If you do nothing, Windows tries to apply voice corrections: echo cancellation, noise reduction, etc. It's not being malicious. It naturally assumes you're a salesperson calling into the home office, conference call or stockholder's meeting. Windows machines stopped being general purpose machines a long time ago.

http://manual.audacityteam.org/man/faq_ ... hancements

Using SWAG engineering (Scientific, Wild-Ass Guess), I'm going to say the heavily processed gaps in the voice are throwing Zencaster off. Zencaster has to have some way to know if a person hung up to know when to terminate the connection. Sudden, unexplained perfect silence is a darn good way to tell. Normal people with normal microphones never get good silence. It's one of the things that messes up reading for audiobooks.

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Re: Audio drift and external sound cards

Permanent link to this post Posted by benuski » Wed Oct 18, 2017 7:44 pm

Yeah, he has Windows 8.1 on a dell laptop with a Samson Meteor microphone. Is there anything in Windows settings that I can turn off that might make this work better?

Another one of my podcast mates uses Windows 10 and has not been having problems, so maybe it is a Windows 8 specific thing?
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