Topic: weird wav form

[ts]

opened up a wav file in audition and  . top half of each wav form is peaking at -2 to 0 and bottom half is around -6 where i would have expected it to be based on my recorder settings. never had this before. recording sounds OK, maybe a tad funky. first thought i had was the caps overloaded. any ideas.

[bgreen]

Sounds like it could be a bad case of DC offsett?

[page]

once or twice or constantly that much difference?

[ts]

once or twice or constantly that much difference?

constant, all the way across. if i knew how to do a screenshot i'd post it

edit for screenshot. not the wav mentioned in first post, but you get the idea. this was the opening act and same thing happened just lower levels. i was running nakcp701's(modded Cm700's)>722. opening act normal gain. second act low gain. phantom set to mics and line in. switches in mic position. didn't realize this till it was too late, but can't imagine that being the cause. it was a stack tape, but not humping the stacks, about 20 rows back.

[page]

1) Your equipment tests out fine when you repeat this at home with some random CD?
2) Not a brass band was it?

[ts]

page, yes, at home test was fine and no, not a brass band, but brass in the band. Dave Matthews Band.

My first thought was also overload because of the history of the mics I'm using. I'm using the regular barrels when most most folks that have this mod (Franken Nak type mod) use the -15db attenuator barrels. I've used this setup many times before and have never seen a wav form like this one. Although this is probably the loudest show I've taped with this rig.

What does asymmetrical overload sound like? The recording sounds OK. It's a little thin, but that could be from my location and mic characteristics. It does sound like it's missing something, can't really put my finger on it and there is no obvious distortion.

mshilarious here is a zoom in segment of DMB wav. The bottom half of each wav is what I would have expected to see based on where my levels were set. The top half was the surprise. There was no hard clipping in the top half during the entire recording, so that is probably why I have no audible distortion. Don't suppose there is anyway of compensating for this in post?

[ts]

Still not zoomed in enough.  Can you just post a link to a 30 sec clip instead?

Nothing you can do about a distorted wave, but you can remove DC offset.  Most software has a tool to do that, but try using a 10Hz high-pass filter instead, that can remove DC offset as well as other strange gremlins.

I've never posted any sound clips. What do I use to do it? I'd be happy to try.

Does Adobe Audition have a DC offset tool or where in Audition is a 10Hz high-pass filter? It's the only software I have. Sorry for the stupid questions, but never had to deal with this before.

Is this zoom better?

[heyitsmejess]

ive had that problem before.

came from a near-dead battery in the preamp.

[fmaderjr]

Does Adobe Audition have a DC offset tool or where in Audition is a 10Hz high-pass filter?

High Pass Filter in Audition 3.0:
Effects/Filter & EQ/Scientific Filters (process)
Select High Pass tab at bottom
Set cutoff to 10Hz

Corrects DC offset pretty well for me.

[ts]

Does Adobe Audition have a DC offset tool or where in Audition is a 10Hz high-pass filter?

High Pass Filter in Audition 3.0:
Effects/Filter & EQ/Scientific Filters (process)
Select High Pass tab at bottom
Set cutoff to 10Hz

Corrects DC offset pretty well for me.

Thank you! I did that and some quick filtering on the low end and the recording seems fine. I still think I experienced that asymmetrical overload. A switch to the -15db attentuator barrels should correct that.

[SmokinJoe]

Tony,

I had a very similar looking waveform a couple of times with 2-wire AT853's... which are known to brickwall/overload at "loud" levels... where "loud" is a relative term.  Going from a 9V to 12V battery box seemed to reduce it in my case.  A friend had a similar situation with some chopped Nak 300's when they were fed with a low input voltage (in the 3V range). Given at least 6V, his Naks work better.  Other people have seen similar results when Nak 300 batteries are getting weak.

I don't know enough about Nak700's, or the mod that's done, to comment if that's whats likely to happen.  Obviously the -15db attenuator barrels seems like the logical next step.  I would think if the capsules are starving for voltage, then attenuators won't help that.  If the caps have enough output to overload the FETs then attenuators would do it.

Joe

[ts]

Tony,

I had a very similar looking waveform a couple of times with 2-wire AT853's... which are known to brickwall/overload at "loud" levels... where "loud" is a relative term.  Going from a 9V to 12V battery box seemed to reduce it in my case.  A friend had a similar situation with some chopped Nak 300's when they were fed with a low input voltage (in the 3V range). Given at least 6V, his Naks work better.  Other people have seen similar results when Nak 300 batteries are getting weak.

I don't know enough about Nak700's, or the mod that's done, to comment if that's whats likely to happen.  Obviously the -15db attenuator barrels seems like the logical next step.  I would think if the capsules are starving for voltage, then attenuators won't help that.  If the caps have enough output to overload the FETs then attenuators would do it.

Joe

Hi Joe,

I'm not sure about the low voltage. What would a wav form look like with a low voltage problem? Wouldn't both the top and bottom of each wav/channel be affected? I know those screenshots suck, but the top half of the wav is the part that was way wrong. The bottom half is what I expected to see based on where I set my levels. I'm leaning towards the asymmetrical overload that mshilarious described, or at least started to, he hasn't been back.

This mod is the same as the Nak 300 mod. Utilizing the barrels for an "active" type of setup. I'm using the AT 8533 power modules. 48V to 9V adapter. The 700's run on 6 volts. I've run these modded Naks with both sets of barrels. I did about 5-6 theater type shows with the -15db's>722. Even from the 5th row at the Beacon I had to have the gain on the 722 beyond 3/4's. It was the same at most other shows with those barrels. I switched to the regular barrels and found the levels to be more predictable and I never had this "overload" problem I experienced here.

I hope what happened was a combo of a loud DMB stack tape and no attenuation in the barrels. A switch back to the attenuator barrels should solve this problem for loud shows, so I've been told. I'm probably the only person with modded 700's that uses the regular/0 attenuation barrels in their mod. Everyone else uses the -15db barrels and they even go as far as stating that the regular barrels are useless for loud PA recording. I guess I was bound to get burned sooner or later.

This is the part I really don't get. I had the 722 set on low gain anticipating an overload problem. I don't understand where the overload happens. If the caps overload before the FET, does the attenuation in the barrel catch that and any setting on the pre is too late?

Always appreciate your input Joe.

Thanks, Tony

[SmokinJoe]

My distorted wave forms happened to be flat on the top, not on the bottom, and when I saw yours I thought of that, but I just figured that was a source/follower design difference, not a symptom of a different problem.  I know mine were "one sided" as well, not just squished top and bottom.  Your issue and my issue might well be from completely different issues.