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Recording Fault

Jul 26, 2012 3:28 AM

Okay, I'm trying to help somebody else with a problem in CS5.5 and it has me puzzled.  (And I'm pretty sure it's his hardware, not Audition btw.)

 

He describes it as the wave form go crazy every few seconds on his speech recording--but the audio keeps playing back though with some level issues sometimes.

 

I went through the usual litany of reinstall drivers, shut down back ground stuff etc. etc. to no avail and finally had him send me a short sample of the problem.  It's very strange.

 

This first pic is the whole waveform and you can see the "splats" every so often--but it all does indeed playback without the expected noise:

 

Problem Wide.jpg

 

Going a bit tighter, you can see that the glitches are some form of very LF wave:

 

Problem Medium.jpg

 

...and going in very tight, you can see the modulation on the LF waveform--in this case speech--that plays back in Audition:

 

Problem Tight.jpg

 

My next instinct was a problem with his interface (Focusrite Scarlet 2i2) but he says he's tried an old Tascam interface and got the same result, maybe a bit less frequent.

 

FYI there's an audible noise on the whole file as well.

 

Any thoughts?  Only thing I can come up with is a fault USB port on his laptop letting some voltages creep in.  Any other ideas gratefully received!

 

Bob

 
Replies
  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
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    Jul 26, 2012 6:11 AM   in reply to Bob Howes

    Hmm.......................

     

    I'll give you a possible clue - that looks very much the way that mains-borne interference does when you record it....

     
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    Jul 26, 2012 6:44 PM   in reply to Bob Howes

    Sometimes I've experienced hard drive servo stuff contaminating the chassis ground in the laptop.  So those disruptions could be each time the disk seeks or something.  I'd hook up a meter to the headphone-out on the built-in sound chip on the laptop to see if it coincides.

     

    To confirm, however, it plays back _WITHOUT_ the noise you see in the waveform?

    That is, this is just a cosmetic issue of the waveform?

     

    Also, does this happen with the built-in sound chip, or just the Focusrite?

     
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  • SteveG(AudioMasters)
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    Jul 26, 2012 7:19 PM   in reply to Charles VW

    Charles VW wrote:

     

    To confirm, however, it plays back _WITHOUT_ the noise you see in the waveform?

    That is, this is just a cosmetic issue of the waveform?

    He didn't say that; he said "FYI there's an audible noise on the whole file as well."

     

    I like the possible case grounding problem as a cause in principle, but that's going to be one helluva ground fault - I'd be surprised if the machine didn't show other faults as well. If the power to the USB was glitching, that could explain it - in which case the effect will at least alter if you supply power to the Focusrite externally.

     
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  • SteveG(AudioMasters)
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    Jul 27, 2012 7:16 AM   in reply to Bob Howes

    Bob Howes wrote:

     

    I'd love to try the Focusrite self powered but, alas, it's ONLY bus powered.

     

    (I have to admit I'm somewhat gratified that it's not something obvious I've missed.)

    Er, there is...

     

    Run the Focusrite via a powered hub? That will stop the internal power having anything to do with what happens in it. If it changes anything at all about this, that's at least a clue.

     

     

    Bob Howes wrote:

     

    I hear a constant wavering "whine" at quite a low level throughout but the guy with the fault hasn't mentioned that.  Just look at the waveform on the "silence" there's certainly something there.

     

    Well that's definitely a case of 'measure amount of weird', because that shouldn't be happening. And what's more, most of these sorts of noises generally do get traced back to power, grounding-type fault conditions. Can't find any other references to this sort of problem with starlets though - and like you mentioned, the tascam does this too. How is it with the internal sound device on the laptop? And what sort of laptop is it?

     
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  • SteveG(AudioMasters)
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    Oct 26, 2006
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    Jul 27, 2012 8:13 AM   in reply to Bob Howes

    Bob Howes wrote:

     

    Doh!  should have thought of the powered hub (though whether he will buy one as a diagnostic tool I don't know).

     

    Well he ought to. They cost 4/5ths of bugger all...

     

    And look on the bright side - at least it's not a Dell.

     
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  • SteveG(AudioMasters)
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    Jul 29, 2012 3:21 AM   in reply to Bob Howes

    Does that also account for the whining noise?

     

    In fairness, I should have realised that if the fault was identical with a completely different interface, that it was unlikely to be the interfaces at fault!

     

    Know what you mean about elevated train lines though. Built a small studio some years back at the rear of Sheperd's Bush market, right next to the elevated section of the Hammersmith and City line. Yeah, I know that's supposed to be part of the underground network, but nobody told them that... and it produced a lovely rumble every few minutes. I told them what we'd have to do to fix it completely, but they came to the conclusion that moving the entire studio elsewhere would be cheaper, so that didn't happen. Instead I designed some slightly weird-looking mic mounts that they could use, but they came to the conclusion that since they were mainly going to use the studio for speech, they'd just roll off the bass - ie, a cop out. Needless to say, nobody I know is prepared to use it now.

     
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