student wrote: (the best for me will be every 0.5 or 1 sec)
That seems to contradict what you described here: viewtopic.php?p=283690#p283690
If you zoom in close on the waveform you will see that it is constantly going up and down. If you simply take the values of samples at arbitrary intervals the result will be virtually meaningless.
If you want good advice, it really would help if you described exactly what you are trying to do. If you're not bothered about the quality of the advice, then we can carry on like this.