Some people might find it strange that dc offset removed is lumped together with normalization effect. The reason is that in mathematics, normalization usually involves offset shifting and re-distributing of data, and dc removal is the offset shifting part.
In audio recording, dc offset is almost always a hardware problem. While you might not hear it, the problem can be see from the waveform as it is shifted above or below 0.0, as shown in the figure below. In my simple recording to make instructional videos, I have never encountered problem with dc offset, so this figure is manually generated for illustration purposes.
While a small amount of dc offset is common, a large amount indicates a hardware problem. If you have a large amount of dc offset, you should try to find out what the hardware problem is and fix it instead of simply using software to correct the offset.
To correct/adjust the dc offset without doing any other adjustment, use the “Normalize” effect, select “Remove DC offset (center around 0.0 vertically)” and deselect other options.
Click “OK” and your waveform should be adjusted as shown below. Notice how the signal is now centered vertically around 0.0.
If you have any DC offset, Audacity manual recommends that it should be editted as the first step of editing, before other editing is performed.
Since there is no parameters or value that you need to enter as you do dc offset removal, this is not really an effect that this series of articles are focusing on, but I am including it for the sake of completeness.
In next article we will look at the actual normalization process and the parameters involved.