UNbalanced signal: sound captured off the middle line (main cause of all the noise?)

[helleeno]

Hello, everyone!
Since I've installed Adobe 3.0 on this very notebook I've been using for around 3 years, all of what I record is shown below the middle line of the track. It's like the sound is not being captured with balance, or the balancing channel splitting line is being placed off of where it should be.

After applying "Noise Reduction (process)" (100%, by the way) on a track (the very one on the illustrating picture), that track was placed right on the middle line, and started sounding cristal clear.

Any ideas of what could be causing this "malcapturing"? Mic cable, the mic itself, the PC mic input, ASIO4ALL, bad set up software, etc...?

Thank you all once again!

 

[Track Rat]

DC offset.

 

[sjjohnston]

Exactly.

I don't know Adobe, but it probably has a way to remove the DC offset without doing anything else. In other words: don't run noise reduction, remove it the correct way.

More generally: the fact it first appeared when you installed Adobe kind of suggests Adobe is the culprit, which seems bizarre to me. It'd have to be seriously bad software to do that - or you'd have to have set some option in a way that seems really unlikely, if it's even possible. One thought: the offset might be produced by your hardware, but whatever your old software was automatically removed it.

In any event: if it is produced by the hardware, you want to fix it there, rather than just correct it. It's stealing headroom, for one thing. If the PC mic input is the soundcard built into a laptop, that would seem the likeliest culprit.

 

[sjjohnston]

On a separate point: I don't know what the recording is you're showing in the picture. If that was audio you're trying to make sound good, you might want to have it peak a little bit higher than -15 dBFS.

 

[Bobbsy]

The DC bias adjustment in Audition is under Effects/Amplitude & Compression/Amplify-Fade(process) menu. There are various options about how to process and how much processing to do. There are also DC bias options under Options/metering in order to give you accurate metering even in the face of severe DC offset as seen here.

In the longer term, a better audio interface would almost certainly correct the DC Offset before it happens.

To sjjohnston, DC Offset is produced ONLY in hardware--it's not a software issue. Audition only records what the sound card is giving it. Normal audio is a purely AC electrical signal but faults in soundcards can superimpose a DC voltage on the audio causing it to appear above or below "the line".

Also, on the topic of levels, it depends on what the OP is recording. If it's a transfer from an already-compressed recording then you're right that you can push the levels higher than seen here. However, if it's a live voice or instrument with lots of dynamics, -15 isn't a bad place to aim for. Don't forget that 0dB(FS) is equivalent to about +18dBu so the -15 levels you see are equivalent to about +3dBu. The other factor is that DC Offset affects the metering, making the source look a lot hotter--hence my mention of the Audition option to correct the metering for DC Offset.

Bob

 

[helleeno]

Hello everyon! Before I get started, I want to thank you guys for the attention.

So, two things I've done tonight in order to solve the problem:

1) Talked to the sound engineer in whose house I've recorded tonight.
2) Looked for "solving DC Offset" in Google. And by the way, thank you guys again for revealing me this technical term I wasn't familiar with. That sure will help me a lot from now on.

The engineer told me the same sjjohnston did: the likeliest culprit should be hardware. In his words: "usually it happens when you have bad quality hardware", meaning soundboard rather than anything else. Also, he told me it used to happen all the time in his early home recording days.

As far as Google, it dropped me into Adobe's website, and there I've fund a nearly magical solution: Amplitude and Compression> Amplify/Fade (process)> DC Bias Adjust, which does visually the same that Noise Reduction (process) did, which is to place the sound waves DC Offsetlessly. Of course, Noise Reduction removed the noise, but the sound captured started sounding like a bad quality mp3 (sort of underwater feel). Amplify/Fade (process) did not remove any noise, but did correct the positioning of the waves.

Finally, I've found Options> Metering> Adust For DC. That made the meters move almost evenly when capturing in Stereo, and totally evenly when capturing in Mono. However, it didn't correct the positioning of the waves, but only placed them nearer the center line. Also, it seemed really curious to me that as I set the mic's sensitivity from 0,0dB, to +10, +20 then +30dB (maximum), the soundwave would go further below the center line, being 0,0dB over the line, +10dB the closest it would get to the line; +20dB already below the line and +30dB even further below.

Well, I'm still getting A LOT of noise. And sjjohnston, when I get the sound to peak that high, it's inaudible from all the noise I get.

To sum up:
1) I guess I've checked all possibilites on solving DC Offset problem, on Adobe Audition;
2) Now I guess my problem would be noise, which I tough was a consequence of DC Offset, which apparently is not.

So now, concerning noise, would that be a mic or cable problem?

Long reply, hope you guys have the patience. Thank you!