Topic: Unbalanced postive/negative amplitude problem

[hurleytom]

I hope I'm posting this on the right board. I finally got around to recording a gig last night with my stealth rig for the first time (SP-CMC-4, SP-SPSB-6, Edirol R-1). However the audio on the right channel is a bit unbalanced - the negative peaks max out at 0dB (-100%), while the positive peaks max out at about -3.5dB (about 70%), while silence is centred around 0%. You can see a screen shot of what I'm talking about in the attachment below. You'll also see the left channel is unaffected.

I guess I have two questions:
What caused this to happen (CMC-4s, SPSB-6 or R-1)?
Is there a way normalize only the top half of a wav in Adobe Audition or something similar?

[hurleytom]

After some messing around with Adobe Audition and trying to remember some engineerin mathematics I figured out to solve my problem!!

Here's how I did it (this is for Adobe Audition 1.5, but I'm sure this could be adapted for other software) and what I started with::



1. Copy right channel to a new mono wav (right clicked -> copy to new).
2. Effects -> Amplitude -> Normalize -> deselect normalize and DC Adjust to -100%

You should now have the bottom part of the wav cut off, leaving only the positive values:



However DC is centred around -100% so it needs to be moved back up to 0%. If you DC Adjust back to 0% with Adobe Audition it gives components below DC that we don't want:

< - Rubbish!!!

So instead:
3. Copy to a new mono wav (right clicked -> copy to new).
4. Effects -> Amplitude -> Normalize -> deselect DC Adjust and normalize to 0%
5. Effects -> Amplitude -> Normalize -> deselect normalize and DC Adjust to +100%



This give you a DC level at 100%. This can now be added to the wav obtained after step two:

6. Copy
7. Edit -> Mix paste... -> Overlap (Mix) -> 100%

You should now have something like this:



This can now be normalized to 100%:



Now all you have to do is go back to the original right channel and repeat the process to get the bottom half:

8. Copy right channel to a new mono wav (right clicked -> copy to new).
9. Effects -> Amplitude -> Normalize -> deselect normalize and DC Adjust to +100%
10. Copy to a new mono wav (right clicked -> copy to new).
11. Effects -> Amplitude -> Normalize -> deselect DC Adjust and normalize to 0%
12. Effects -> Amplitude -> Normalize -> deselect normalize and DC Adjust to -100%
13. Copy
14. Edit -> Mix paste... -> Overlap (Mix) -> 100% with wav from step 9.

This should give you something like this:



You can then use Edit -> Mix paste... -> Overlap (Mix) -> 100% to mix the two halves together:



This can be then copied back into the original stereo wav and the left channel normalized.

[BayTaynt3d]

Dude, what were you taping? Were there brass instruments? If so, the asymmety is perfectly normal.

[hurleytom]

It was a friend's rock band in a pub setting. Is there any reason why one channel would experience asymmetry and not the other?

[BayTaynt3d]

Brass or no brass?

[hurleytom]

Sorry, no brass, just guitars, drums and vocals...

[BayTaynt3d]

Ok. That is strange.

[69mako]

I had the same situation happen to me what I taped a rock band years ago.  But with my situation, it happened with both channels.  also in a small club.

Mako

[guysonic]

I hope I'm posting this on the right board. I finally got around to recording a gig last night with my stealth rig for the first time (SP-CMC-4, SP-SPSB-6, Edirol R-1). However the audio on the right channel is a bit unbalanced - the negative peaks max out at 0dB (-100%), while the positive peaks max out at about -3.5dB (about 70%), while silence is centred around 0%. You can see a screen shot of what I'm talking about in the attachment below. You'll also see the left channel is unaffected.

I guess I have two questions:
What caused this to happen (CMC-4s, SPSB-6 or R-1)?
Is there a way normalize only the top half of a wav in Adobe Audition or something similar?

If not knowing better, I'd think the SPSB-6 was putting out a large DC component that offset the audio.  Usually there's a DC blocking/audio coupling capacitor removing the Mic's DC bias, allowing just the audio (AC component only) to pass into the deck's mic input. 

In your case, either there's a fault with the SPSB-6, or a problem with the R-1's native mic powering circuit that is allowing mic powering DC bias signal into the first mic stage, and offsetting the audio.  Anyway, that's what I think is happening if the deck has operated OK before using the mic input.

[hurleytom]

I was going line-in on the R1. The thing is that there doesn't appear to be a DC offset because silence is balanced around DC/0% - it's just the negative values of the signal that appear to be amplified more than the positive ones.

[guysonic]

I was going line-in on the R1. The thing is that there doesn't appear to be a DC offset because silence is balanced around DC/0% - it's just the negative values of the signal that appear to be amplified more than the positive ones.

Knowing about using Line input helps eliminate the deck's mic powering as the problem.  Another thought is it may actually be a mic capsule fault.  Maybe do a test at home close to a speaker using the mic as before with powering module into line input (make sure the module battery is good), if still seeing the imbalance, disconnect the module and try running the mic directly into the deck's powered mic input jack. 

The deck's mic powering voltage is less at ~2.5 volts, but the mic should still operate in OK for testing manner.  While the mic signal may be reduced, you should still see if there's a problem with one of the capsules showing one channel not operating at same output level, and maybe with offset of sorts that's different from the other channel. 

If not seeing the offset, then more likely the powering module has a problem, or mic capsule shows fault only when running at higher 9 volt bias voltage supplied by the battery module?