recording sound drop off

[mancshaun]

i am usinig a dynamic mic through a pre amp in to the Line in on my laptop and i have tunred anti virus off. if i record silence i will get general background noise for around 2 - 10 seconds then the background noise dissappears completely. 2 things happen when i am recording voice. 1. if i begin talking before this drop off the recording will be fine but occasionaly during a pause in talking the drop off can occur, at which point my voice has noise when i speak. 2. if i dont begin talking before this drop off the whole recording will sound noisy and muffled. i have found that this also happens if i monitor input.
any ideas folks??

[steve]

My guess is a low quality soundcard, or perhaps a USB headset - what are you using?

[mancshaun]

the mic is a shure pg58 connected via a Maplin preamp direct into the mini jack Line in on my laptop. the soundcard is a Sigmatel high def card. i tried updating the drivers and they are the most up to date i can get. something new that has just started happeninig is, the recording is working fine then all of a sudden the sound being recorded begins to stutter very fast, any ideas on that too???

[steve]

Sigmatel high def card

That's an "on-board" sound card isn't it? On-board sound cards are never the most reliable for audio work (sometimes they are not just poor, but appallingly bad). Check to see if there is some kind of "Automatic Gain Control" (AGC) set in the sound cards graphical interface (Mixer, control panel, or whatever GUI it has).

something new that has just started happeninig is, the recording is working fine then all of a sudden the sound being recorded begins to stutter very fast, any ideas on that too???

"Stuttering" is usually caused by something preventing the audio data from being read or written quickly enough.
There can be many causes -
An anti-virus update may cause your anti-virus program to interfere,
Any newly installed programs may have services running in the background that hog resources,
Running short of disk space, or disk fragmentation
A virus, Trojan, or spy-ware
....

It's worth doing a "clean up" of your computer - delete old unused files, old restore points, empty the Recycle bin etc. to free up some disk space, then do a THOROUGH anti-virus and anti-spy-ware scan of your complete system, then defragment your hard drive. Reboot your machine and shut down all non essential programs and processes. Audacity is then likely to run much better.

[boober]

I can verify this!!! I have a dell laptop (d620) with the "sigmatel HD audio"

I am using a sony stereo condenser mic (with a battery in it) plugged into the the mic in on the laptop. I have verified that the problem is not the mic using a minidisc recorder.

In Audacity, I was getting the seemingly random jitter/muffle that you describe, but I found the fix for this was to change the number of recording channels to 2(stereo) in the recording setting under I/O in preferences. I have no idea why this would fix the problem, but it's just one of those things I guess...

Anyway, that took care of that crap, but there does appear to still be some kind of AGC that kicks in after about 3 seconds (that you describe... once the background noise is gone, it's gone unless the threshold/ceiling is broken) built into the sigmatel audio hardware that have not found a way to toggle.

[steve]

but there does appear to still be some kind of AGC that kicks in after about 3 seconds (that you describe... once the background noise is gone, it's gone unless the threshold/ceiling is broken) built into the sigmatel audio hardware that have not found a way to toggle.

If you find a way to switch this off, please do post the solution. This question has come up several times in relation to sigmatel HD audio.

[mancshaun]

Cleaning up my computer seems to have stopped the stutter but nothing i do will stop the sound drop off. i work in IT and have contacted Dell and it would appear even their own engineers know of the problem but have no fix for it.