Weird looking audio peaks

Lili wrote on 3/14/2006, 4:48 PM

I just finished capturing an hour-long video of a speaker that was wearing wireless mic and I notice that the audio peaks on the timeline look unlike any other I've seen. The top section is barely there and the bottom peaks are the normal height, but appear very dense.

I notice that the speaker's mic is clipped about halfway down his tie. I usually mic a speaker higher up. Could this be the reason? The audio is not as crisp and clear as I would like either. Probably same reason?

Comments

Spot|DSE wrote on 3/14/2006, 5:02 PM

Sounds like you have more than just placement going on. I'd wager that you had a preamp problem, transmitter problem, or other gainstage problem. Were you using unbalanced cable on a long run? Wireless?

Lili wrote on 3/14/2006, 5:14 PM

I was using a wireless - Sennheiser EW100 - also noticed that the first 20 seconds have normal peaks and then it just suddenly changed.

Bob Greaves wrote on 3/14/2006, 5:44 PM

Sounds like DC offset. There are free plugins available to correct it.

kdm wrote on 3/14/2006, 6:57 PM

I would say DC offset if you have some waveform above, continuing below (i.e. top half of a full cycle just looks shorter than the lower half), but if it looks like the top half was cut off, leaving you with spaced lower half waves, that could be a partial connection or bad ground in the mic path - you get half of the phase - a half cycle wave - no, or few sparse peaks above the 0db line, and normal below, or vice versa

There isn't much you can do to recover from the latter, but if you have DC offset, you can compensate for it - how much to compensate for may take some trial and error.

farss wrote on 3/14/2006, 8:46 PM

SF has tools for measuring and correcting DC offsets however I really doubt this is the problem. As DSE said most likely something has gone wrong in the mic preamp in the transmitter or the mic itself or it's somehow been overloaded which you do have to watch out for with the Sennheiser RF mics.
And sorry to say it's very hard to fix.

Bob.

Spot|DSE wrote on 3/14/2006, 9:40 PM

my suspicion would be it's a transmitter overloading the receiver and the receiver being set to low output. If it's DC offset, the center point of the waveform will be off the zero point of the audio track. If it's DC offset, the levels should look somewhat "normal" but not aligned with zero. It's usually a simple fix, but it appears that you've got more than that happening here. Hard to say based on description, as you've got a couple very experienced audio guys with totally different answers. Like blind men describing an elephant. :-)
Can you post a screenshot with audio track enlarged?

Lili wrote on 3/15/2006, 6:11 AM

thanks for all replies - I will look further into it when time permits, and will also post a screen shot as DSE suggested - (I would have done it already, except that I'll have to do a search and refresh how to post one and don't have the time right now as the client, after stalling for 3 weeks to provide me with some critical information needed to finish two - hour-long dvd's, now wants them by tomorrow!).

It will be interesting to see if the audio for the second speaker will be the same - will find later today after I capture. thanks again:-)