Topic: What the? Strange Waveform?

[BayTaynt3d]

Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?

[anodyne33]

preamp issue. one side of the waveform +v (i'd suppose) got more voltage (or possibly less) than the other for some reason at that passage

[BayTaynt3d]

That's strange. What could cause something like that? I haven't checked the second act yet (this was the opener), but I'm hoping it's not a problem there. I ran DINA for the second act and moved my rig, so I'll check that tonight.

[Roving Sign]

Is there anything to hear? Does it sound normal in those passages...?

Sometimes - soundguys will pump up one channel while they work on some EQ issues - that can cause sudden blasts if energy- that arent necessarily noticeable live...

...but I see what your saying about it being lopsided...

[BayTaynt3d]

The lopsidedness is on both channels though. It sounded OK on first listen, but I haven't spent any quality time with it yet really -- I just opened it up last night and saw this weird section. There is some clipping in those regions as far as SF determines. But it's not like it's favoring one channel or something, this is happening in one channel's waveform.

[Roving Sign]

I meant "channel" relative to the board mix/inputs...not left or right main output...

For example - he might have bumped up the drum overhead mics - did some EQ work - and them bumped them back down...but while they were up - they might have caused some peakyness in the overall mix...

just an example...

[Electric Cowgirl]

It looks like severe overage to me.  Open up the level meter and play that section.  If you are slamming the zero that's all it is.

[BayTaynt3d]

I've had penty of overages before, and clipping, but the waveform is always still uniform. There's got to be more to it than that. Only ONE SIDE of the waveform is having an overage. WTF? This just doesn't seem to be a case of "levels to hot" to me. The waveform is ASYMETRICAL?

[terrapinj]

PM Sent

[cleantone]

I think it is what dot ron mentioned.

[SparkE!]

You didn't say what your recording chain is.

My first mics (homemade) made lopsided waveforms like that when run into my PCM-M1.  I later replaced my coupling caps with polypropylene caps (they were originally tantalums) and that cured most of the problem.  The problem was also not as bad when I ran them into a NJB3 because of the higher input impedance on the NJB3 as compared to the PCM-M1.  I made a few more mods later that were designed to reduce even harmonic distortion and I don't see anything like that anymore.  So, I'm betting that it's your mics or your battery box (if you use one).

[BayTaynt3d]

Chain was: CK391 > UA5 (BM2+) > JB3

It was the first night out with the 391's (I usually ran C4s). And I also think I used a spare DVD battery that I got with the FP24 I bought a few weeks back. So, I had some new things in the mix that possibly could had contributed maybe?

The good news is that the first and second sets of the main act look fine (see attachments). Not sure what happened on the opener though. Strange. I wonder if the caps ended up touched each other in my XY on the opener if that could have done it? I was running XY on stage, and although the opener wasn't miced through the PA, there was a crapload of mics and cables on stage for the main act that had 20+ artists in it, every one of whom was mic'ed. Not sure if I could have had problems with that. The main act, I pulled back to the sweet spot for the PA and went DINA, so I had a pretty different setup for the second part.

[Roving Sign]

when you first mentioned the possibility of the mics touching - I thought you were refering to mechanical noise caused by them bumping each other. But maybe - if they touched - there is some electrical contact/interaction.?

[BayTaynt3d]

There was a point, well into the set, where I looked up, and I thought they were literally touching each other for the rest of the set. By that point my levels were fine, and I was off having drinks. My stand was on stage practically, so I didn't have to guard it. When I saw it, there was nothing I could do about it because it would have been rude and distracting to try to fix it. I'm still not sure if they were actually touching or not, but maybe. Good reason to put the windscreens on though. Then even if they were touching, it wouldn't be direct contact. But still seems strange to me. I'll have to watch it over the course of the next few pulls.

[CHURCH-AUDIO]

This could be the front of house sound engineer bumping up a fader on his main system EQ. I do this from time to time to see if I have a bump in the front of house or if its comming off the stage monitor mix and when I hear something on the verge of feedback I will do it to see if its me or the monitor engineer. But still its strange its only on the + side of the wave form. Hummm maybe it could also be a sampling error?. Here is another theory What if the +- voltages on your computers PCI buss were out if you sound card is internal or even if you have a external with a voltage rail problem the opamps would have a swing towards the + or - depending on the design of the circuit.
Hey maybe its just a screwed up waveform? how does it sound?


 

Chris Church

Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?