This is less of a blog post, more of an instruction tutorial on how to make seamless audio properly as I seem to be finding myself trying to explain this often...
In games it's often necessary to make audio perfectly loopable -- whether it's a combat music track or simply the hum of the vehicle's engine, and making any sound loopable is actually pretty easy in Audacity -- a free tool for editing audio.
1. Start by opening the track in Audacity and selecting it (CTRL+A).
2. Click on the end of your track and paste the copy (CTRL+V) so that it's effectively duplicated at the end.
3. Hold Shift and use the scroll wheel with the mouse over the time slice to zoom in in order to get a closer look. What you can hear, you can also see -- and if there is a break in the smoothness of the audio waves, then there will be a noticeable discontinuity when the track loops. In my case, there is one, so onto the next step!
4. Choose the Tracks -> Add New -> Stereo Track (or just Audio Track if you're working with a mono sound). This adds a second layer, just like in Photoshop.
5. You can now choose the Time Shift Tool to move the track down and make it overlap a little by dragging it down with the mouse. When working with music, try to match the waves so that they align. Ideally you want to overlap a few seconds of audio if possible. With music it's often easier to align by seconds as it generally has a consistent beat. In my case I overlapped exactly 2 seconds at the end.
6. Select the overlapped section by choosing the Selection Tool again and hit Space to listen to it. Does it sound proper, or is it all disjointed? If it sounds bad, then you didn't align the waves properly. Go back to step 5 and move the second layer around on its timeline until it matches and sounds better.
7. Now it's time to cross-fade the audio, making it blend. Select the top overlapped part and use the Effect -> Cross Fade Out. Repeat the process with the bottom track, but this time choose Cross Fade In. The idea is to make the audio of one track fade out while the audio of the second track fades in.
8. Time to combine the two tracks into a new one: CTRL+SHIFT+M, or choose the Tracks -> Mix and Render to New Track menu option.
9. We now have a track that blends nicely, but the blend happens right in the middle of this new track, and we want it to be at the beginning and the end! Let's select the blended track's section, copy it, then paste it onto the new layer. CTRL+C, zoom out with the scroll wheel and paste the segment on the first layer by clicking on its end -- then use the Time Shift Tool again to snap it into place.
10. Delete the second track. We no longer need it. Just click the "X" button in its top left corner.
11. Select the entire first track's length on both layers. We don't need it anymore either. Just drag with the mouse after choosing the Selection Tool again and click the "DEL" key on your keyboard.
12. Almost there! Zoom in on the end (Shift + scroll wheel) and select the more complete track's section right below the pasted segment and delete it as well (DEL).
13. CTRL+A to select everything, Tracks -> Mix and Render. And there you have it! A perfectly looping track. Export it via the File -> Export Audio menu option.
I hope this explanation helps someone else. I had to figure it out by experimenting, and there's probably a better way -- but this one works for me.
