Hello, for my game I use openAL and want to extract loops for example for engine sounds. However, it is not so easy to cut pieces out of existing recordings so that the resulting loop is smooth and you will not hear where it has been cut. I use audacity, and when cutting I am looking for zero crossings, but this is not enough. Can you give me some hints how to create nice loops? Thank you very much. Michael

I don't know if it's possible in Audacity, but a simple way is to select a small region of the waveform while the wave editor plays the selection in loop. Then enlarge the selection until you hear a nice sound.

Well I use Soundforge 8 for this. You do need to look for zero crossings and then using the crossfade tool might help smooth things out.

The important thing to do is not to set up the looping points too close together and to try your best to make the waveform as similar as possible where the looping points are. It isn't enough to just have matching zero crossings- what happens if the peaks (the distances the waveform reaches going away from the X-axis) differ great at each point? You'll get a wobble in the sound. Sometimes this isn't a problem and can work for the kind of SFX you're wanting- other times it can become very distracting.

I hope that helps!

Nathan

Ok, thanks, cross fading might help.

Two further questions, if you don't mind:

1. When you do crossfading, how large is the crossfaded portion related to the whole loop length?

2. When we look at a sample basis: Does zero crossing really mean, that the first sample is exactly to zero,. i.e. 0x0000. What about the last one in the loop. Also exactly zero? If we have a completely periodic signal it is not clear to me, why this zero crossing is relly an issue....

Thanks,

Michael

The cross fade zone should be relatively small. In Sound forge it is set to a ratio and I usually pick between 25-35%. The important thing is to experiment and see what sounds best to you.

You can actually have the waveform not cross at zero- but it is important to make the waveform is connected. For example what happens if you have one point crossing slightly above the X-axis and the other slightly below the X-axis? You'll have a clip or bump in the sound. I think most people use the zero crossing because it is easier to identify visually and most programs supporting cues for zero crossings.

Ok, thanks, I will try it.

Michael

PS. Are you related to the Jazz piano player "Peter Madsen"?

I don't think I'm related to him- but Madsen isn't that common of a last name either. ;)