Recorded Volume Randomly Varies...

[Argh]

I've used Audacity for years and recently tried to use it to record spoken material directly from our soundboard. When I do, the volume (amplitude of the waveform) gets loud rather suddenly and then gets soft rather suddenly. This repeats throughout the recording. I simultaneously recorded the material on a cassette and the volume is well balanced. In fact, when I record from the cassette to Audacity, the waveform amplitude is consistent.

Here's how I have the recording set up:
I take the output from the soundboard in the auditorium and run it back to the platform (where the PC is located) through a snake. It comes out a MIC connector, through a direct box into the MIC input on the PC.

Thanks in advance for any thoughts you may have.
~Steve

[MDOC]

Suspect electro-magnetic interference that fits the pattern of droning in and out the way you described. The interference may be anywhere, in the snake or in the sounmd room. To isolate, run another cable through a different route.

[kozikowski]

<<<the pattern of droning in and out>>>

Well, maybe, but the complaint isn't additional noise. The complaint is the performance volume changes erratically. It does bother me that you clearly don't have the computer wired right. Laptop PCs tend to not have Line-In (unlike Macs) and instead settle on Mic-In. There's quite a difference between them.

My web site conveniently went down, or I would post pictures of the difference. The feed coming from the sound board is probably line (high) level stereo and the cable going into the laptop (if it's a real Mic-In) is mono (Left only) with computer battery voltage on the wire where Right would normally be. That and Line level is 1000 times louder than Mic level. So nothing about this is right. I bet the direct box doesn't much like having 6 volts battery applied to the wire normally associated with Right audio.

I know this is rough, but can you inspect the bouncing green sound meters and tell if the difference between the two volumes (high and low) is about 6. Say when it's OK, most of the bouncing is around 3 and when it gets quiet, it drops to about 9--a difference of 6. I know doing this on voice is very difficult.

You know you can get something like this if the audio connector in the side of the laptop isn't pushed all the way in, or the plug is slightly dirty. Scrub the plug with a paper towel and alcohol/Windex/vodka and then dry thoroughly with another towel.

Koz

[MDOC]

Upon re-reading, I rather suspect a problem with the soundboard, not the snake cable. Your connecting the cassette isolated the problem.

[kozikowski]

<<<the pattern of droning in and out>>>

Well, maybe, but the complaint isn't additional noise. The complaint is the performance volume changes erratically. It does bother me that you clearly don't have the computer wired right. Laptop PCs tend to not have Line-In (unlike Macs) and instead settle on Mic-In. There's quite a difference between them.

My web site conveniently went down, or I would post pictures of the difference. The feed coming from the sound board is probably line (high) level stereo and the cable going into the laptop (if it's a real Mic-In) is mono (Left only) with computer battery voltage on the wire where Right would normally be. That and Line level is 1000 times louder than Mic level. So nothing about this is right. I bet the direct box doesn't much like having 6 volts battery applied to the wire normally associated with Right audio.

I know this is rough, but can you inspect the bouncing green sound meters and tell if the difference between the two volumes (high and low) is about 6. Say when it's OK, most of the bouncing is around 3 and when it gets quiet, it drops to about 9--a difference of 6. I know doing this on voice is very difficult.

You know you can get something like this if the audio connector in the side of the laptop isn't pushed all the way in, or the plug is slightly dirty. Scrub the plug with a paper towel and alcohol/Windex/vodka and then dry thoroughly with another towel.

Koz

[MDOC]

<<<the pattern of droning in and out>>>

Well, maybe, but the complaint isn't additional noise. The complaint is the performance volume changes erratically. It does bother me that you clearly don't have the computer wired right. Laptop PCs tend to not have Line-In (unlike Macs) and instead settle on Mic-In. There's quite a difference between them.

My web site conveniently went down, or I would post pictures of the difference. The feed coming from the sound board is probably line (high) level stereo and the cable going into the laptop (if it's a real Mic-In) is mono (Left only) with computer battery voltage on the wire where Right would normally be. That and Line level is 1000 times louder than Mic level. So nothing about this is right. I bet the direct box doesn't much like having 6 volts battery applied to the wire normally associated with Right audio.

I know this is rough, but can you inspect the bouncing green sound meters and tell if the difference between the two volumes (high and low) is about 6. Say when it's OK, most of the bouncing is around 3 and when it gets quiet, it drops to about 9--a difference of 6. I know doing this on voice is very difficult.

You know you can get something like this if the audio connector in the side of the laptop isn't pushed all the way in, or the plug is slightly dirty. Scrub the plug with a paper towel and alcohol/Windex/vodka and then dry thoroughly with another towel.

Koz

LOL, you got a problem?

[Argh]

Thanks for the replies. A couple notes:

1. The PC is not a laptop. It's a desktop with a regular soundcard. I tried line-in, but it didn't work at all. Maybe I should check it again.
2. The PC is running XP Professional.
3. The plug is clean.

I will look at the difference between the meters when I can.

I guess my plan right now is to somehow get the direct-box out of the loop. The return I am using has a microphone jack on the end -- like this: http://images.apple.com/pro/techniques/ ... ectors.jpg Maybe I should do some soldering and just put a 3mm jack there.

[Argh]

Upon re-reading, I rather suspect a problem with the soundboard, not the snake cable. Your connecting the cassette isolated the problem.

Thanks, but the cassette recorder was not connected to the same place as the PC. It was connected right into the soundboard. Maybe I should carry it to the platform and plug it in there to see if it gets the volume variation.

[MDOC]

Don't use the mic input, use line in input. You'll need to set the line in as the default in the sound app in the control panel.



You also need to set up the preferences in Audacity accordingly in the Audio I/O tab.

[Argh]

OK -- In order to make sure it wasn't something with my external hardware, this morning, I plugged a PC mic into the mic-jack on the workstation in the front of the auditorium. Then I set Audacity to listen to the mic and I spoke several lines of text in monotone. And as before, the volume randomly varied. This leads me to conclude it's not a problem with voltages, the direct-box, or any external sources, but something in the PC itself.

The PC is running XP Pro. The soundcard is onboard (C-Media AC97 Audio Device). I am using Audacity 1.2.6.

In Audacity, I have selected Edit / Preferences / Audio IO Tab / Recording Section / Device and selected both the "C-Media Audio Device" and the "Microsoft Sound Mapper - Input". In each case, the randomization occurs.

Monday I plan to order a replacement soundcard, unless someone has further suggestion as to what my problem may be. I welcome any suggestion as to what soundcard to buy. I don't want to spend lots of money since this workstation is used only for PowerPoint presentations, some home-video, and recording spoken words.

Thanks for all the replies and suggestions to date and those to come.
~Steve