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Offul Duster
Known Participant
April 11, 2017
Answered

Help with attempts at DC offset in 3.01

  • April 11, 2017
  • 1 reply
  • 1455 views

Hi guys,

I am having problems with my understanding of DC offset.
So I thought I would show you the problem by way of some images...
1.

First, here is part of a waveform

It is a recording in mono from a cassette tape deck. Other tapes playback in the same way.
When I look at it, I notice that the top parts of the waveform above the RED line seem larger than the corresponding part of the waveform below the line.

2.

So I select normalise, and choose Normalise to -0.5db, plus a DC Offset of -3%.

The idea is to move the waveform down the screen to centre things higher, so that effects are the same above and below the red line. (I guess my understanding here is rubbish...  🙂   )

3.

So, this seems to be correct.

4.

But I have doubts..
So guys, does that now mean everything is ok and compression etc will be correct on both the + and - side of the red centre line?

Thanks in advance for any corrections to my understanding

Pete

This topic has been closed for replies.
Correct answer ryclark

No that isn't really DC offset. All audio signals are non linear to some extent, particularly the human voice and brass instruments due to the sound being produced by the air making the sound moving predominantly in one direction. So it is nothing to worry about.

Any level alteration be it amplification, normalization or compression should retain the difference in + and - going excursions of the waveform. If you try to make them equal you will actually be adding distortion! So in your image the red ringed peaks should keep their relative offset. Amplification/normalization of the marked part which is at present -3dB on the positive side and -7dB on the negative would, for instance, with a gain of +3dB end up as 0dB and -4dB. With compression the difference between the peaks will become slightly less depending on how much you apply.

1 reply

ryclark
ryclarkCorrect answer
Participating Frequently
April 11, 2017

No that isn't really DC offset. All audio signals are non linear to some extent, particularly the human voice and brass instruments due to the sound being produced by the air making the sound moving predominantly in one direction. So it is nothing to worry about.

Any level alteration be it amplification, normalization or compression should retain the difference in + and - going excursions of the waveform. If you try to make them equal you will actually be adding distortion! So in your image the red ringed peaks should keep their relative offset. Amplification/normalization of the marked part which is at present -3dB on the positive side and -7dB on the negative would, for instance, with a gain of +3dB end up as 0dB and -4dB. With compression the difference between the peaks will become slightly less depending on how much you apply.

O
Offul DusterAuthor
Known Participant
April 12, 2017

Thank you Ryclark.

Your explanation is much appreciated.

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