Topic: Non-Symmetrical Waveform?

[stevetoney]

Can someone explain what's happening when you get a non-symmetrical waveform after loading a recording into your DAW software.  Please see the image I've posted below...note that this one isn't all that bad, but once or twice I've seen this happen where the positive phase  peaks are alot higher than the peaks on the negative phase.

Is this caused by how I've got my gear set up, or by the music I'm capturing (what's it called 'phase bias')?  FWIW, this only seems to happen to me occasionally, and as recently as last weekend for one bass heavy performance during a festival where neither of the shows before or after have this issue.

Is this something that can or should be 'fixed' in post?  If so, how do you go about fixing...what would be a typical DAW tool to use?

Thanks to anyone that can help with this question.

[fmaderjr]

I believe this is an example of DC offset which I occasionally run into in my recordings.

It probably sounds fine as recorded, but I believe the offset should be repaired, if possible, because when you apply further processing to a recording with DC offset it can cause problems with the processing that can lead to increased distortion.

To repair in audition, Google turns up that you can load the recording into audition, right click on the level meters, and select "repair DC".

I use Audition and never knew this. What I have done in the past, and you can try if this doesn't work for you, is to use Scientific Filters/High Pass Filter and Nuke everything below 20 Hz (maybe even below 10 Hz would work).

[dlh]

I've seen this before too, just recently, in fact.
I just pulled up the track, check statistics, dc offset reports 0%.
I hit "Repair DC offset" and saw no change.
I've never heard anything weird about these tracks.
Cubase says:
"This function will remove any DC offset in the audio selection.
A DC offset is when there is too large a DC (direct
current) component in the signal, sometimes visible as the
signal not being visually centered around the “zero level
axis”. DC offsets do not affect what you actually hear, but
they affect zero crossing detection and certain processing,
and it is recommended that you remove them."

Maybe someone here has had a bad experience they can share.

Dave

[Smokey]

Could this be what Jon described in his reply to another topic just a few days ago?  Specifically: "soft clip in capsule FET: one side of the wave is squished but not flat, other side may look normal".

http://taperssection.com/index.php?topic=156655.0

I have one particular recording where this occurred for the first and last 30 minutes of the performance but the rest appeared normal. That leads me to think it was something outside of the recording chain, like a significant change in PA levels during the show.

[dlh]

All I've found so far:
http://www.audiomisc.co.uk/asymmetry/asym.html

Interesting that it shows asymmetrical waveforms on loud piano and trumpet.
My most recent experience is with a trumpet track.

Dave

[stevetoney]

Now that you mention, I do think one of my more assymmetrical waveforms was also a horn based band.  In the case of the exaCEmple i've shown above, zoogma is a bass heavy sorta tance ish band (with no horns).

[dlh]

scroll to joeq's reply
http://www.gearslutz.com/board/so-much-gear-so-little-time/739730-strange-looking-waveform-one-particular-mic.html

[rjp]

I've also encountered asymmetrical waveforms in some human voices, as well.

[page]

Interesting that it shows asymmetrical waveforms on loud piano and trumpet.
My most recent experience is with a trumpet track.

yep, welcome to the world of brass. Short of the tuba, I'm not sure there is a brass horn that doesn't do this. I've seen it in trumpets, trombones, all sorts of stuff.

[Massive Dynamic]

I just noticed the non-symmetrical form in several of my recent recordings. Is there a good reason not to make removal of DC offset part of one's standard post-processing workflow? Seems very easy and took only a few seconds to perform.

EDIT: I did an analysis of a couple of asymmetrical waveforms and found that there was virtually no DC offset (.004%). Here's a fairly on-topic GS thread.