Strange waveform phenom with cheap mics

K

KenekeBarnes

New member
On some cheap mics, such as a computer mic (and some dynamic mics I have), a recorded sound will have a visual waveform that is larger on top than on bottom, and sometimes the lines even skew off of the center line. Since most sounds (and whatever is recorded on my better mics) have a mostly symmetrical waveform (top/bottom) what causes this inequality?
 
Asymmetrical is normal, but sometimes a bit of distortion in the chain can make them peak higher on one side.
 
yeah, cheap computer mics (or cheap mics in general) and/or cheap soundcard, you could have some DC offset. basically, a DC signal is getting into what's being recorded, which you don't want of course.

often you can't audibly hear the DC Offset, but then again, sometiems you can. eitherway, get rid of it - it eats headroom.
 
Stop looking at the pretty pictures.

Most waveforms, especially vocals are asymmetric.

Listen to the sound... if it sounds good, it is good. If it doesn't sound good looking at the pretty pictures ain't gonna help.
 
Fletcher said:
Stop looking at the pretty pictures.

Most waveforms, especially vocals are asymmetric.

Listen to the sound... if it sounds good, it is good. If it doesn't sound good looking at the pretty pictures ain't gonna help.
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well, if it's DC offset that's a problem. Your speaker cones won't be returning to their resting point. The offset also consumes headroom. Not to mention if he's mixing two tracks together, one with offset and the other without, the resulting stereo track will just combine the problem and it will also have an offset.
It's good that he's noticing the problem and he should fix it.
 
bennychico11 said:
well, if it's DC offset that's a problem. Your speaker cones won't be returning to their resting point. The offset also consumes headroom. Not to mention if he's mixing two tracks together, one with offset and the other without, the resulting stereo track will just combine the problem and it will also have an offset.
It's good that he's noticing the problem and he should fix it.
Click to expand...
Agreed. Offset is also one of those rare problems that's not always readibly identifiable by sound alone; you might hear an issue because of decreased loudspeaker efficiency, and because you start clipping earlier than expected, but it often does not have a sound of it's own other than a possible (but not guaranteed) pop at the beginning or end of playback. It's a rare case in this instance where the fact that one cannot hear it in and of itself does not mean that it's not cramping the rest of the recording.

G.
 
mixsit said:
Asymmetrical is normal, but sometimes a bit of distortion in the chain can make them peak higher on one side.
Click to expand...
Yes - true. I'm not sure if asym always means there's a DC offset. It seems to me I pushed too hard into one of my preamps and the waveshape looked asym - I'm thinking the DC offset looked OK though...my memory might be foggin up though.
 
What causes me to think that the OP has DC offset and not just an asymmetrical wave is his statement

"and sometimes the lines even skew off of the center line"

If when recording true silence (e.g. mute is on) your level is flatlining above (-inf)dBFS, you have offset, which really needs to be filtered out before you continue.

If OTOH, you simply have asymmetry in the waveform but the centerline is still truely centered, and all sounds proper to your ears, then that's probably just the natural order of things and is probably OK.

G.
 
SouthSIDE Glen said:
What causes me to think that the OP has DC offset and not just an asymmetrical wave is his statement

"and sometimes the lines even skew off of the center line"
G.
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Haha - thank you Mr. Holmes - that would seem to indicate an ugly offset! :D
 
Let's keep in mind though that problematic DC offset really is pretty rare... And that many sounds have a "naturally occuring" asymmetry to their wave - Many vocalists, a lot of percussion, most horns - It's certainly not an unnatural thing.

My question would be *what* is being recorded and what is the chain like. There needs to be some troubleshooting - Is *everything* asymmetrical with *all* microphones and *all* preamps?
 
Massive Master said:
My question would be *what* is being recorded and what is the chain like. There needs to be some troubleshooting - Is *everything* asymmetrical with *all* microphones and *all* preamps?
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no apparently it's not. supposedly only one of his microphones is causing this (the cheap ones he says)

it still all goes back to his comment about the zero point not really resting at zero.
 
Awesome discussion, this helps a lot. Thanks guys!

- Yes, stock sound card on PC.
- No, can't hear a hum
- Clean vocal input, no EQ or FX
- Like I said, it doesn't happen with my better mics; it's nice to know yet another reason to go for quality mics.

Thanks again!
 
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