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Unusual Distortion

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Tom Prigge
Unusual Distortion
on Aug 15, 2013 at 3:11:04 am

I’m having a weird distortion problem recording voice over. Some background: I just purchased a used ADK Hamburg mic (the original, not the new model). I tried it out and it sounded fine. But then, the mic stand fell and the mic hit a carpeted floor rather hard. No visible damage and nothing is rattling inside the mic. But now about 50% of the time, I get a weird distortion and the recording sounds sped up. A link to a short sample is at the bottom of this message. This sample happened in the morning before leaving for work. I went home at lunch, turned everything on and did a quick “Testing 1-2-3” recording and that recording sounded fine.

Here is my setup—ADK mic via Mogami silver XLR cable into a Scarlet 2i2 interface into a Win 7 laptop running Audacity freeware. The laptop is not powerful, but fully capable of running Audacity. Prior to this setup, I used an AT 2020 USB mic into Audacity and never had a problem.

When recording, I have my headphones plugged into the Scarlet’s headphone jack. I do not hear the distortion or strange speeding up. I am not pegging the needles either (I was a DJ back in the days of vinyl)—so I can’t imagine that is the source of the distortion.

If the mic were damaged, wouldn’t I hear it through the Scarlet’s headphone jack? Could it be the Scarlet? Latest drivers are installed and Audacity recognizes it. And again, everything sounds fine in the headphone jack.

I am recording onto my D drive, not my C boot drive.

And of course, the problem is intermittent. But I don’t know it is messing up until AFTER I have recorded. I don’t monitor through the computer because the latency makes it impossible.

For those of you who listen to the sample, have you ever heard anything like this before? Any help or insight will be appreciated.

http://f1.creativecow.net/file/6408/6408_weirddistortion.mp3.zip


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Bill Davis
Re: Unusual Distortion
on Aug 15, 2013 at 6:01:20 am

Total guess, but I suspect maybe a capacitor (or another component in the circuit somewhere) is going bad.

Kinda makes you wonder if that is why the original owner was selling it?

If it persists, you've got to get it to a qualified tech who can put it on a tracing scope and wait patiently until it screws up - and he or she can see what's actually happening.

But clearly the waveform is getting trashed at somewhere between the diaphram and the recording. And I'd suspect it's at the mic's own electronics.

Again, all wild supposition. But it mostly sounds to me like what you'd hear if a circuit component is failing.

Anyone else?

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Andrew Rendell
Re: Unusual Distortion
on Aug 15, 2013 at 11:32:21 am

I rather agree with Bill, I see it's a FET+bipolar design and I think it's the kind of thing you hear when the supply or bias voltage is screwed.

Intermittency might mean it's a cracked track or dry joint rather than a failed component, but that's something of a guess (partly informed by my experience that physical shock is more likely to cause a failure in the wiring / connectors than component failure these days). So, stumbling in the dark really, but my gut feeling is that if an engineer looked at it on the bench they might identify the problem with a magnifier and AVO meter without needing to turn the scope on.

[TBH, my experience of "front line maintenance" (wielding a meter and soldering iron to keep tape decks running) is a good few years past, I only really get involved at component level with electric guitars these days, so please don't take this as anything more of a diagnosis than a possible sign post.]

BTW, the Scarlet 2i2 should let you monitor it's input without going through the computer - that would be a very good thing to do (plus it's another way of eliminating any other possible source of the problem, e.g., if it sounds ok there but you get a distorted recording then the problem isn't with the mic - it's very easy to assume that the problem is at one point in the chain without actually eliminating everything else when something like the mic being dropped makes it "obvious" that's that's what must be wrong).


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Ty Ford
Re: Unusual Distortion
on Aug 15, 2013 at 12:00:38 pm

Hello Tom and welcome to the Cow Audio Forum.

Sounds to me like you may have a mismatch in the sample rate or channels. Back in the early days, speeding up or slowing down was sometimes due to something as simple as choosing mono versus stereo. Maybe you clicked on the wrong thing on a panel somewhere.

The glitches were there to tell you something wasn't quite happy. You may need to adjust Audacity or look for a new software driver.

Try the mic on another computer. If you get the same results, it could be the mic, but still may be a driver issue.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Tom Prigge
Re: Unusual Distortion
on Aug 15, 2013 at 1:09:56 pm

Bill and Ty--Thank you for the advice. Do you think I can rule out the mic? Through the headphone jack on the Scarlet 2i2 I do not hear any weirdness whenever the recording goes bad. Wouldn't I hear it through the headphone jack if the mic was the problem?


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Peter Groom
Re: Unusual Distortion
on Aug 16, 2013 at 10:24:54 am

Im with Ty
Sounds like a digital mismatch.
Sample rates mismatch or 1 device locked to a different speed than the other.
Peter

Post Production Dubbing Mixer


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Tom Prigge
Re: Unusual Distortion
on Aug 16, 2013 at 1:02:11 pm

Thanks to everyone that replied. Looks like it might have been the mismatch. I had Audacity set at 16 bit 48k. The Scarlet 2i2 default is 16 bit 44.1. I've matched them up and so far, so good.


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Peter Groom
Re: Unusual Distortion
on Aug 16, 2013 at 8:34:07 pm

I knew it.
I once had to create a very similar effect on a track which I deid by mismatching sample rates .
Peter

Post Production Dubbing Mixer


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