Volume Gets Lower While Recording

[jdycus]

I am trying to record a 30 second segment from a tape player to my pc using Audacity. The first 5 seconds or so record perfectly, then the volume starts getting lower so that the last 20 seconds or so are barely audible. Anyone have any idea what is happening? Thanks

[steve]

How is your tape player connected to your computer? Through a sound card "line in" mini-jack connector?
Is the soundcard a PCI soundcard, USB, built into the motherboard, a laptop microphone socket?

While you are recording, does the recording meter in Audacity show the input signal getting lower?
If you monitor the input with Audacity (Click on the Recording meter to enable the meter) without actually recording, does the same thing happen? Does it eventually go silent, or does it stabilise at a lower level?

[jdycus]

How is your tape player connected to your computer? Through a sound card "line in" mini-jack connector?
Line in mini jack

Is the soundcard a PCI soundcard, USB, built into the motherboard, a laptop microphone socket?
Built in to the motherboard

While you are recording, does the recording meter in Audacity show the input signal getting lower?
Yes

If you monitor the input with Audacity (Click on the Recording meter to enable the meter) without actually recording, does the same thing happen? Does it eventually go silent, or does it stabilise at a lower level?
stabalizes at a lower level

[kozikowski]

<<<segment from a tape player>>>

Do you have an iPod or any Personal MP3 Music Player? Music CD player or portable computer with iTunes or other music service?

Set your tape player aside for a minute and connect anything else to the Line-In of your computer. You may need one of these if your music player has RCA outputs.

http://www.radioshack.com/product/index ... age=search

Or one of these if it doesn't.

http://www.radioshack.com/product/index ... age=search

Record a minute and I bet the problem isn't there. If it is, then your computer sound card is failing.

Koz

[jdycus]

Still didn't help, but if my sound card is failing, wouldn't that show up in playback as well? My problem is only in recording.

[steve]

Still didn't help,

So you get the same problem using different input sources (tape player / ipod / etc.)?

but if my sound card is failing, wouldn't that show up in playback as well?

Not necessarily - if you have a leaking capacitor or something like that in the analogue circuitry at the "front end" of the recording input, then the input gain could be unstable and produce these kinds of symptoms, but it would only be on the recording side, not on playback.

[kozikowski]

So to recap. You changed the connection and sound source to your machine and the problem didn't go away. Did you try to record a bit using Windows Sound Recorder instead of Audacity? I'm betting that would have troubles, too.

<<<Windows Sound Recorder
Start -> Programs -> Accessories -> Entertainment>>>

For all practical purposes, the only thing in the middle is the sound card. I will lean on theory here for a second. The place likely to cause troubles like this is the analog pathway before the show becomes digital. Once you get digital ones and zeros, it takes quite a bit of intentional work to change the volume. Digital failures arrive as blasts of noise, holes, very high distortion, etc. No volume changes.

Letting my right brain go nuts for a second...are you really sure you plugged your show into the Line-In of your computer and not the Mic-In? You never told us if you're working on a Laptop or not. Most (but not all) PC laptops have Mic-In and not Line-In. Can you find both connectors? Plugging a Line level signal into a Microphone connection will give you unstable results.

Koz

[steve]

it takes quite a bit of intentional work to change the volume.

With you mentioning the "Mic Input", it suddenly made me think of the possibility of AGC

We had better have the make and model of the audio device, and what the Operating System is.
I believe Vista has the facility for Automatic Gain Control and it may even be included in some soundcards (though that's not something that I've come across before).

Also, are there any other audio programs running (such as Skype) that could be interfering with the audio system?
Does the problem also occur with Windows Sound Recorder?

[jdycus]

After reading all your posts, I have concluded that I may have a combination of problems: (1) my pc is a notebook with no line in, only a mic in, and (2) I think my built-in sound card may have AGC control. I'm going to purchase a line to mic adapter and see if that solves my problem. Thanks for all your help

[kozikowski]

<<<line to mic adapter>>>

Yes, that should get rid of the mic channel overloading problem and I have built those myself (they're six ten-cent resistors in a box, so don't pay hundreds of dollars for it), but you need to know that the signal will become noisier than if you had used a Line-In connection in the first place. The converter will add noise and then the microphone amplifier inside the computer will add more noise. Line-In connections go straight from your sound device to the digital converters with no or few additional electronics in the middle, so they're much quieter.

However, if that's what you have, that's what you have.

Koz