Topic: My waveform looks funny (details inside) PLEASE HELP!!!

[Javier Cinakowski]

I  was hoping someone could explain why my waveform looks the way it does. The problem is in each channel. Look at the bottom peak of the right channel then the top peak of the right channel. The right channel is not centered in the grid. The top of the wav is louder than the bottom (not right or left) That does not make much sense, but hopefully someone will know what im talking about. thanks for any help folks!!  I might not be explaining this very well so I will included a picture. Anyway, what is casuing this and is it a problem?

PS: it is not CoolEditPro's problem as I tested some other wavs. It is not the microphones or recorder because I have done other recordings with them and the wav's look fine. The only variable is the preamp. The preamp is brand new and sounds fine however. What is the deal here, anyone know? Thanks again for any input!!!!

[Javier Cinakowski]

not the DC offset.  The wave form is centered but the + cycle of the wav is louder than the - cycle or vice-versa.  I measured for the offset it is -.001

[mmmatt]

have you opened it in other editing programs?  This is pretty wierd.  I was going to say DC offset too, but if cool edit is saying now then I'm stumped.  Try opening it in Audacity (free, decent program.  Google it)  if you don't have another wav editor.

Matt

[Javier Cinakowski]

I opened the wav in EAC's wave editor.  It looks the same.   I have been out of taping for a few years and I forgot about the frustrating parts. 

[thunderbroom]

I've had this show up on a couple of shows.  I rewired my battery box and it seemed to take care of it.  I thought it was a dc offest at first as well.

[Javier Cinakowski]

Dear Murph,
 
Our preamp is built around an ultra low noise transistor, not a chip (IC).  The transistor is biased class "A" for low crossover distortion and ultra smooth linearity.
the artifact you are seeing on the amplitude waveform is nothing to worry about, it's simply the biasing resistors on the transistor base being slightly unequal. This is due to the 5% tolerance on all our parts. 
 
This will, in no way, affect the sound or performance of your preamp.
 
If you have further questions, please don't hesitate to call me.
 
Best regards,
 
Jon Enoch
E.Eng.
Visivox Technologies.

[Chuck]

I don't think this is "nothing to worry about."
As others have noted, it looks like DC offset, which IS something to worry about.
5% matching is not that great. High quality microphone pre-amps have 1% or better matching for the phantom power biasing resistors.
Do you know if the circuit is surface mount or through hole design? If the latter, it would be easy to swap those suckers out for better and more closely matched resistors.

[mmmatt]

how does it sound?  Is there anything audibly wrong with the file.  I find it a little odd that it is symetrical.  I unfortunately don't know enough to fully understand this either.  I'm curious now though!

Matt

[Javier Cinakowski]

I don't think this is "nothing to worry about."
As others have noted, it looks like DC offset, which IS something to worry about.
5% matching is not that great. High quality microphone pre-amps have 1% or better matching for the phantom power biasing resistors.
Do you know if the circuit is surface mount or through hole design? If the latter, it would be easy to swap those suckers out for better and more closely matched resistors.

Well, the preamp was rather inexpensive, thus 5% matching is probably fair.
I have no idea if the preamp is surface mount or through hole design.  The screws on the box are so tight I think they might be glued and im not sure I wanna take a chance on screwing it up.  I would love to swap out the resistors but frankly I do not know the first thing about resistors or where to get a better quality matched set.

If someone could verify that "this is nothing to worry about" than I would be happy to forget about it.  If someone could explain why this is a problem (other than the wave looking funny) than I would seriously think about a resistor upgrade.  I like the preamp
I really do not know what to do.  [edit: 5% variation]
The preamp sounds fine, which makes this even more confussing.  Does "hear no evil see no evil" apply here?
Thanks again for the input!!

[George]

I think I know   

Say, how does the actual wav file sound?  Is there distortion?  Was it a loud concert?  I taped a very loud show in a small bar a while back and it looked just like your wav file, only it sounded fine, it was just a very loud show.  Show us a zoomed up pic of the wav file.

[mmmatt]

have you tested the rig and tried to record something at home and repeat the error?

Matt

[anodyne33]

I'll say that it's nothting to worry about. It WILL however make you more prone to distortion if you're REALLY pushing the levels. If you want we can meet up and I can open 'er up and see if there's anything we can do. If it's SMT I won't go near it with a 10 foot pole, but if it's discreet we can certainly give 'er a tune up.

[Javier Cinakowski]

Thanks for the responces everyone.  The concert was fairly loud in a small bar. 

Why will the preamp be more prone to distortion at high SPL's because of this issue?  I really don't understand exactly what is happening because of this 5% variation in parts.  Is there a seperate part for amplifying the + and - sections of the wave cycle?  Am I even on the right track in understanding this? 

If I am understanding this right it has something to do with the phantom(9v) power parts instead of the actual preamp stage.  Thus, if i used a mic that was allready powered (like a NT5 or dynamic mic), and turned the phantom/PIP switch off the problem should be avoided. However, that does not help with the MM-HLSCs(9v bias required) that I just bought and really like.

..........  I grew some balls and opened this thing up.  It had a touch of glue holding it together after I took the screws out.  Other than the glue it was easy to open.  I will email the pics to you .ron. 

[poorlyconditioned]

Thanks for the responces everyone.  The concert was fairly loud in a small bar. 

Why will the preamp be more prone to distortion at high SPL's because of this issue?  I really don't understand exactly what is happening because of this 5% variation in parts.  Is there a seperate part for amplifying the + and - sections of the wave cycle?  Am I even on the right track in understanding this? 

If I am understanding this right it has something to do with the phantom(9v) power parts instead of the actual preamp stage.  Thus, if i used a mic that was allready powered (like a NT5 or dynamic mic), and turned the phantom/PIP switch off the problem should be avoided. However, that does not help with the MM-HLSCs(9v bias required) that I just bought and really like.

..........  I grew some balls and opened this thing up.  It had a touch of glue holding it together after I took the screws out.  Other than the glue it was easy to open.  I will email the pics to you .ron. 

Can you please send me pics (or post them here?).  I want to see the insides!

As far as the waveform goes, perhaps it is "brickwall distortion".  That is, the mic input is overloading before it gets to the preamp.  If this is the case, then you want a 3-wire battery box on the input.  I can't tell for sure though.  How does it sound?

  Richard

[Javier Cinakowski]

As far as the waveform goes, perhaps it is "brickwall distortion".  That is, the mic input is overloading before it gets to the preamp.

Well, I doubt it.  The mics are rated at like 160SPL with 9vp power. The preamp is basically a battery box with a preamp.

 I will post a .flac sample of the recording in a minute.

drop me your email and I will send you the pics.  Im not sure I want to post them here.