Modulation During Recording

[andy3825]

Hey, I'm Andrew, I'm new to the forums. Felt an introduction was needed.

Anyway, I was recording my acoustic guitar today with an AKG C2000, about a foot from the 12th fret, gain at around 10, as part of my music tech class (hearing different mic positions and such). The recording peaked a little bit with a hard strum, but at one point the recording modulated a half step up. I have never heard of this sort of thing happening, but it happened right after a peak which is the only possible reason i could think it happened.

Recordings done afterwards were perfectly fine, the cables are all in tact, and the recording was done straight into the computer, no preamps, eq's, etc.

I was wondering if anyone has heard of this sort of thing, knows what the problem is, etc.

 

[crazydoc]

You mean it changed key?

If you're going "straight to the computer" what is your source of phantom power?

 

[yaknski]

I'll bet it was just the PC "coughing". It does happen sometimes.

 

[dementedchord]

dont feed the trolls....

 

[andy3825]

Changed key, yes.

I'm sorry, we ran it through an m-audio ozone academic keyboard to the computer, which gives phantom power but doesn't/can't really have any sort of effect on the sound.

 

[danny.guitar]

The sample rate on your computer could have changed for some reason...is it using a stock sound card?

Were any websites open? Did an ad pop up? Were any media players open? Anything that could have possibly tried to play video/audio?

 

[Rimshot]

By any chance.........

Were you playing a Joni Mitchell song? They tend to modulate without warning, a lot!

Sorry, but it sounds like another program in your 'puter chain just having some fun at your expense.

 

[andy3825]

Yeah, it's a stock soundcard on one of last years iMacs.

I'm just glad we didn't screw up the mic or something crazy.

Thanks for the suggestions.

 

[ittam]

I don´t dare to play at all but i have friends
who feel playing ok almost everywhere but
feel mystically uncomfortable listening
their blayback...

Matti

 

[dgatwood]

Yeah, it's a stock soundcard on one of last years iMacs.

I'm just glad we didn't screw up the mic or something crazy.

Thanks for the suggestions.

My TiVo does that periodically. What happened was that a chunk of audio got delayed for some reason (bad block on the hard drive, perhaps) and the audio is time stamped, so the computer tried to catch up and played back the audio at a faster rate. Worth looking in the console (in your utilities folder) to make sure there are no bad block errors or anything....

That said, I've never seen anything like that happen on my Mac before, so I'm a little curious what audio app you were using.

 

[Fooling Pirates]

Burp!

Maybe your Fridge kicked on and created a power surge...

 

[Shadow_7]

Definitely sounds like a power or computer thing. Since you're not recording real to real or anything. Did you apply any sort of plugins to the track after it was recorded? Was anyone else in the room playing tricks on you? Shot glass on the frets? Moved that fret clamp key adjuster thing (whatever it's called). It could also be that your hand position shifted without you noticing it, until you listened to the recording. Some probably more likely than others.

Was the modulation consistent? i.e. one semitone up/down and stayed there? i.e. from point X till the end. Or was it just a couple notes. Was it sudden, or did it slide into the new key? If you were using a synth, did you change sound samples/fonts at that point? (made that mistake once, sampled a trombone on a Bb, instead of an A)

You definitely want to optimize your computer and otherwise disable anything that could affect your recording(s). Not much of an issue in linux since you can give audio realtime priority. But you should still disable any network interfaces (wireless especially). And disable any schedulers. And if there is anything that you don't "need" to be running, then stop or prevent it from running. Not only does it free up resources (RAM plus CPU cycles), which makes things run faster by itself, but it takes out any question marks that could potentially affect your recordings.

Not much of a hassle to do in linux.
# /etc/init.d/networking stop
# /etc/init.d/cron stop
# /etc/init.d/atd stop

Rather ugly in windows. Especially since it restarts everything you want to stop. And otherwise runs automatic updates anytime it feels like it. Even if/when you tell it not to.

I knew someone that had some sort of photo organizer installed that indexed his entire drive hourly. And on that beefy computer he had a big drive. He was wanting to buy a better computer because that one was running so slow for him. Once I pointed out what was eating up his resources, he stopped it and what a difference it made. That was a bad one. Not only did it affect his game play, but he had trouble playing youtube videos when that indexer was running. And we're talking 3GHz CPU, 1GB RAM, and a high end video card.

 

[andy3825]

Stock iMac, no plug-ins, just akg -> m-audio ozone -> built-in input, recorded into garageband. No funny business as far as i know, because we're all stil mesmerized by this here, and i doubt my friends would keep a joke going that long.

Good suggestions though, I'll definitely check the bad block thing. Thanks.