Recording starts normal then fades and later returns

Using the 2.0.2 dmg on 10.6.8
Every week I record an hour + recording via line level input from my wireless lapel Sennheiser mic. Normally no problem. This is a direct setup with nothing extra between the mic and the 2008 macbook pro laptop.

At least 2 different weeks now recording proceeds as normal then sometime say maybe 30min into the recording the waveform shrinks and the audio level dips (like someone was pulling a fader down) to a very small, but audible waveform which may come back up partially and then lower back down and eventually the audio level and displayed waveform will come back to normal level. When the level does come back it rises to nomal say within 5 seconds. This last time I think if was around 10-15minute worth of reduced audio before normal levels were restored.
No one is touching the computer, I can see the unusual waveform before I save the project at all. This last time I heard just a little additional crackly/noise at the very start of the audio level dip.
24bit, 44100 mono recording. Plenty of HD space left.

The previous time the audio dipped and came back up perhaps 6-7 times in 90 minutes of recording.

I used to do this years ago with Audacity on my Powerbook laptop with no such problems ever.
Has no one else ever experienced such a deal? Since it’s been only 2 recordings out of 12 perhaps it’s a little bit hard to reproduce on demand.

Thanks for ideas.
I’m just trying 2.0.3 prerelease this week.

To go with previous topic.
Audacity 2.0.2 10.6.8
Screen wave form.png

wireless lapel Sennheiser mic.

That’s classic batteries. Also most wireless mics have a campander or some kind of auto level control because raw voices tend not to fit in the radio channel. The microphone pack squeezes the volume variations a bit and then the base unit expands the volumes back to normal. Sometimes not. Some microphones leave the compressor in the voice all the time.

Which microphone?

Audacity doesn’t do anything in real time past record, play, and some timers. No filters, no effects. Audacity just gets what the computer gives it.

You can get exotic problems like radio interference that messes with the volume control system. Can you channel hop and see if it goes away? I’d replace batteries right first thing.


Does it do that when somebody close makes a cell call?


This is with the Sennheiser XSW12 system, maybe 60ft max between the mic and the base.
As far as I can know no one is making cell calls.

The mic is using fresh rechargeable eneloop AA’s with the XSW12 it’s run time is 10hrs+ so I don’t think it’s even close to having weak batteries.

I could choose another channel to switch to, though it’s hard to tell in the short term if that has helped anything.


I don’t know that we have any good reference to what the previous topic was…

Topics merged.

I got a little whiplash there.

the audio level dips (like someone was pulling a fader down) to a very small, but audible waveform which may come back up partially and then lower back down and eventually the audio level and displayed waveform will come back to normal level.

We don’t normally do this, but I think the possibility of Audacity causing this problem is zero.

The fact that the sound level is not erratic and that it switches between discreet sound levels points to a compander problem. The beltpack is switching levels to account for performer volume and the base unit is not marching in the same parade.

The newer units have a pilot tone to keep radio interference from affecting the transmission, but that could have gone fuzzy as well. Troubleshooting radio microphones is an artform.

If you have the trouble on an erratic basis, so much the better. I don’t even have good historical experiences to help you. Most people in my world would rather open a vein than use them because of problems like this.

If you bought QuickTime Pro, I believe that will allow you to record sound completely divorced from Audacity. I wouldn’t dream of running a Mac without it. Yes, I understand all that does is peel us out of the equation, it doesn’t help you at all, but I guess it’s worth a shot.

If you could only intentionally cause the problem…

Do you have more than one beltpack? Do you have access to another base unit? I know. Silly Question. If you did, you would have tried that by now.

The performance people here keep wanting me to buy radio microphones for the company because then, “all our problems will be over.”

Think so?


OK. Troubleshooting 101. Break it.

Set up a recording on a quiet day with nobody else around. Start with just background sound – birds chirping, and start talking as you approach the microphone ending very close to the mic talking loudly. Does it do expected things? Do you get odd level shifts? Does it just overload like a regular microphone? You have a good idea/feel about how these things work normally, so stress it and see what happens.

If you do the same shots over and over with the same talent, you could be on the edge of a sound defect and never catch it until the first time the talent shows up with a head cold and the levels change.

Contact Sennheiser or see if they have a forum. I’ve never had a Sennheiser break.


Well, thanks for the ideas everyone. My problem has not reappeared as of yet. I did change the channel/freq. on the wireless mic.

The problem never was related at all as far I can tell to the loudness of the speaker/talent etc.

FWIW I did also up the record sensitivity linein to .9 from .8 and turned down the audio line level out from the wireless base to compensate.

I sure miss the old Marantz tape player recording feature of having a high audio limiting option so that regular audio could be recorded at a good level and sudden loud unexpected things like a cough or such would be gently limited and not overload the the inputs.

The old Sennheiser G2 series which I’ve had great success with had a pilot tone like some have mentioned, but I’m not sure if this XSW12 has one as it is not mentioned. (Less expensive than the G2 series was).

Does any one have an opinion on the merits of the microphone sensitivity setting on the wireless transmitter side? Currently I have it turned all the way down to -30 The possible range is from 0 to -30. With it turned to -30 then the output from the base is turned 3/4 of the way approx. of max level out. If I raised the sensitivity of the microphone up then I would have to turn the audio out from the base down of course. I’m not too sure where the most effective S:N situation would be. Any personal experiences? I should have a look see if I can find any Sennheiser forums that might have an opinion I guess.

Thanks for the ideas.

Hi, glad I’m not the only one who’s had such a problem!

My problem has returned as well as of last week, what kind of input /mic system are you using?

I think I may try hooking up 2 laptops to the same mic line level output and see if I can verify if it’s the mic or on the computer side. This last time it started getting quieter fading down almost immediately after starting to record. It came back normal again eventually and was fine for 20 minutes or more until it had another dip / quieter zone. Sure wrecks the quality of the recording!