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Old 4th July 2007
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Dave Peck's Avatar

Originally Posted by StudioTinPanAll View Post
what is dc offset ??
DC offset is when the entire waveform is not 'centered' around the zero voltage line. It is offset higher or lower. This can be a result of normal acoustic properties of the audio waveform or it can be caused by various types orf electronic signal processing or types of distortion (intentional or otherwise).

It is generally a good idea to correct DC offset before the signal gets recorded to allow a higher recording level (DC offset will reduce the level at which you can record because either the positive or negative side of the wave will clip prematurely since it is offset in one direction or the other). This DC offset correction can be done with a simple high pass filter that is set to a cutoff frequency well below the fundamental of the audio signal. In this application, you don't want the filter to affect the sound of the track, you just want the track re-centered around zero before it goes to the recording device. A HPF will re-center the signal since DC is, in effect, an infinitely low frequency. Therefore, the HPF 'blocks' the DC component of the signal and moves the entire waveform up or down to re-center it around zero. A high pass filter with a very low cutoff frequency like 15 Hz will work fine.

However, the example of the kick drum posted above is not an example of DC offset. If you study the waveform you will see that there is one big transient at the attack, but after that the bulk of the signal is centered around zero and when it fades out there is no DC component left - the flat line between kick drum hits is at zero, with no DC offset. This particular example is just a normal negative-excursion transient.