Input Volume Drops after 15-40 seconds

[bara]

Hi Guys,

Hopefully you might be able to help with this one, as we are totally stumped!!

I work in a school and we have recently purchased a batch of USB mics for the teachers to record the students speaking mocks and exams.
Wierdly on a couple of the teachers laptops whilst recording, the input volume drops to an inaudable volume, and sometimes completely disappears.
It seems to happen after about 15-40 seconds into the recording.
It only seems to happen on a couple of our Dell D620s. Others laptops of the same make and model we have tested seem fine.
We are using a Logitech USB microphone, I have also refered this to their tech support in the hope they may be able to shed some light on this as well.

The set up is Logitech USB Mic, plugged into the on board USB socket of the Dell D620.
We have the laptop plugged into the mains, and have no other USB devices plugged in at all.#
We are running Windows XP Pro(x86)
The only piece of software running is Audacity 1.3.12
All input volumes are set to Max.
I have attached an example, where the volume drops while a student is mid sentance.

Example.mp3

(950.74 KiB) Downloaded 135 times

Any info at this point would be useful, please feel free to ask me any questions.
Thanks for your help
Antony

[steve]

You need to find your microphone settings (there may be a loudspeaker icon near the Time/Date on your Desktop, or you may need to go into the Windows Control Panel).
There will be a setting for "Noise Reduction" or "Echo Cancellation" (or called something similar). You need to turn that effect off. For recording you should normally turn off all effects.

[bara]

Hi Steve,

Thanks for your reply, I have checked through the effects and settings for the microphone, and it doesnt seem to have any effects available.

Thanks for the idea though!!

Ant

[steve]

I expect there will be a setting hidden away somewhere, but I don't have a Logitech USB Mic so I can't tell you exactly where it will be.
I think Koz may have used one these, so I'll drop him a line and ask if he can advise.

[kozikowski]

I have this microphone...

http://www.logitech.com/en-us/webcam_co ... evices/221

Terrific microphone, slightly honky if you record from too far away, but has very nice acoustic "room" noise cancellation (vents on the side of the pickup tube to admit error sound waves) and no, as far as I can tell, auto volume settings. We are using this microphone (second purchase) for instructional sessions between a digital supervisor in San Clemente, CA and our offices in Asia. Works perfectly every night (LA Time).

I just plugged mine into my MacBook Pro and cranked through a 3 minute voice recording with no oddball effects, volume changes or anything to "help" me. It just recorded me reading the LATimes for three minutes and five seconds. I can post the track if anyone's interested.

The most modern Windows machine I have is Windows 2000, so I don't think I'm going to be a lot of help. I will tell you that Windows machines are business tools and there was a business story that moved on the wires recently about one of the Windows/Intel companies finally giving up any pretense of being "consumer entertainment machines" in favor of hard business use.

When a business machine goes into conference mode it does several amusing things. It tries to determine the overall noise level of the room and uses that as a basis to determine whether or not somebody in the room is speaking. It sets threshold points. If you're listening at the far end, you hear velvety silence until someone speaks in spite of the air conditioning noise in the room.

Another serious witchcraft thing it does is try to figure out how long the room echo is so it doesn't send receive voices back down the transmit line. Whole manufacturer reputations are generated by how well they can do this. At the far end, this sounds like your own voice coming back to you very low volume and very late. If you talk long enough, the echo will slowly fade as the machine figures out what to do and when.

All this is happening in the face of, in our case, a twelve time zone difference between all the people in a conference and a complete festival of different conference units. In one evening session (LA Time), we can have a LifeSize, Polycom, and Mirial Windows or Mac machines on the same call at the same time. Most of the time it all works out. Sometimes not. This wasn't near enough pain, so one production had the director in London on Skype Video (on separate computers) and other participants on regular h.323 video conferencing. Somehow, that worked, too, multiple days running.

So in the face of all that, Mrs. Siobhan McGillicudy of Smithfield-Stilton upon Rye plugs her USB microphone into her new Windows machine and tries to record old folk tunes. Chances of success, zero unless she can figure out how to turn all those Windows business tools off.

I was going to volunteer to ship my microphone to whomever wanted to try it out, except shipping costs were likely to exceed the purchase price of the unit -- $19 USD at the local computer store. WalMart $8 USD.

Koz

[kozikowski]

<<<I have attached an example, where the volume drops while a student is mid sentance.
Example.mp3
(950.74 KiB) Downloaded 2 times>>>

The performer is way too low a volume compared to the air conditioning noise in the room. The computer thinks the performer is part of the room noise and subdues it over time. The performer must get much closer to the microphone or turn the air conditioning off.

Or, figure out where the Windows conferencing settings are and turn them off.

Koz

[bara]

Hi Guys, thanks for all your help so far

I never knew windows had a conference settings, any idea where they might be?
The best page I have found online, is: http://technet.microsoft.com/en-us/libr ... 57120.aspx
But it doesnt really touch on audio settings.
Anyone know where these settings may be hiding?

Thanks for all your help so far
Antony

[bara]

Hi Guys,

It seems we have resolved this simply by changing the recording settings.

Default Sample Rate is set to 48000
Default Sample Format is set to 24-bit

and all seems well so far!!

Thanks for all your help
Antony

[steve]

Hooray
(and thanks for the feedback)