how can i center an audio signal?

Question

I'm trying to reconstruct an audio signal, and below is what i got after rescaling.

How can i obtain centered audio signal such as below?

---

SOLVED:

ruoho ruotsi's answer addresses my problem :)

i found someone asked the similar question before

How to remove or filter the drift problem in measured Strain signal?

Answer 1

"Center" isn't the word that I'd use to describe what you want to do. Your signal does not have a zero-mean, so like @Dole suggested you should use a DC-Blocker (DC-Offset removing) filter to get the job done:

Here are your references:

https://ccrma.stanford.edu/~jos/filters/DC_Blocker.html https://ccrma.stanford.edu/~jos/filters/DC_Blocker_Frequency_Response.html https://ccrma.stanford.edu/~jos/filters/DC_Blocker_Software_Implementations.html

the code (from the above links) can be as simple as this, where x is the current sample and y is the filtered sample, while xm1 and ym1 are the x,y from the previous step (i.e. x[i-1], y[i-1]):

  y = x - xm1 + 0.995 * ym1;
  xm1 = x;
  ym1 = y;

Answer 2

Use small High Pass filter. Usually it is suggested to remove the frequencies in the range of 0-200 Hz for speech signals.

Answer 3

Remove DC offset. Either convert to frequency domain and remove bin 0 or just use a very low frequency high pass filter.