Remove DC Offset

  • Thread starter Thread starter Peter B
  • Start date Start date
P

Peter B

Guest
I'm new to home recording.........so new I don't even know if I've posted this in the right forum, but here goes anyway.

I'm using Cubase to record solo sax and sax quartet at home. Everything's going OK, I'm learning fast and my recordings are improving gradually as I get a bit better at micing and using tools like compression, reverb and EQ. There's one function in the Cubase audio processing list that I don't understand though, and there's no explanation of it in the help files so I'm hoping that someone can explain it to me.

The effect is listed as 'Remove DC Offset'. Now if I apply this function to a selected track, I get a progress bar up on screen which runs quickly from start to end in a time depending on the length of the track, and that's it. I can't hear any difference in the track after applying this effect.

So I should be grateful if someone could shove me a bit further up the learning curve by explaining: (a) what DC offset is, (b) How I know if I've got it, (c) Why it needs to be removed, and (d) If it does need to be removed then why is it a selectable function which implies that you have the choice of leaving it there. If it's bad and needs to be removed why isn't it just done automatically to all tracks out of sight and out of mind?

Thanks in advance for a quick lesson on DC Offset.........
 
Let's try.

A "normal" sound wave, when converted to electricity, is an AC signal going above and below zero volts. When you see this converted to a computer file and displayed on your screen, the waveform should be roughly equal above and below the zero dB line down the centre of the display.

However, sometimes a bit of DC can creep into the signal. This causes the sound wave to be moved above or below the centre line. It still plays properly but, since it's shunted above or below the zero dB line, one side of the signal is now closer to clipping.

The DC offset correction fixes this and gives you a symmetrical waveform again.

Why not fix automatically? Well, first, if you have a problem with DC it's best to know about it and try to sort it out at source. Second, just occasionally, you'll get a voice or instrument that gives you an asymmetrical waveform naturally, without DC offset. These you don't want fixed.

Hope this helps,

Bob
 
DC offset is a problem in which the intersections of a wave file are not crossing at zero. You wont hear any audible difference applying a dc offset correction even if you have dc offset in your track. But when you start to add more layers of tracks with dc offset problems you will start to notice that no matter how hard you try you will have very limited headroom. Samples will start clipping at what is audibly perceived as quite low volumes. It makes mastering that track a pain in the ass.

DC-offset.png


Look at the waveform on top and notice how its riding above the line. That is dc offset. If your waveforms look like that. you have a dc offset problem. The waveform at the bottom is what you want.

If you have dc offset the best way to solve it is to find out what piece of gear you have that's causing it. The problem, 9 out of 10 times, is a cheap a/d converter in your sound card. If you have no way of solving the problem (ie. replacing the offending piece of hardware) then that's when you use dc offset correction.
 
OK, thanks very much for the two excellent explanations. A look through several of my recordings shows them sitting dead on the centreline so it doesn't look as though I have this problem, but very useful to know what that function is, and when I should be using it. Your help much appreciated.
 
Hell...I didnt even see Bob's explanation...lol. Good job though.
 
A look through several of my recordings shows them sitting dead on the centreline so it doesn't look as though I have this problem
Click to expand...
I haven't seen a true DC offset problem in 15 years (other than the occasional SoundBlaster recording).
 
I haven't seen a true DC offset problem in 15 years
Click to expand...
That's very useful and encouraging to know as well Massive master, thanks.

By the way.........

Spark his curiosity to find the answer himself and he'll mix for a lifetime...
Click to expand...
Unfortunately there's another possible outcome for us newbies.....

Spark his curiosity to find the answer for himself and he'll be doing it wrong for a lifetime :)
 
Massive Master said:
I haven't seen a true DC offset problem in 15 years (other than the occasional SoundBlaster recording).
Click to expand...

Funnily enough, the only problems I've seen with DC offset have been from people using Soundblaster/Creative Labs cards. Could this be a pattern?
 
The problem of DC offset is commonly caused by using very cheaply made converters.

It can also be detected by hearing a pop or loud click when starting or stopping audio as well as switching out plug ins.

Another remedy to the problem is to use a hpf set above 1Hz
 
You must log in or register to reply here.
Back
Top