donderdag 4 april 2013

The Art of Looping

The Art of looping
Hi everybody!

Melvin here, senior audio designer and animator at Xform for just about two months now and this my first Xform blog ever.

Well kids, today I'm going to tell you a story about a thing called "looping". The reason why I'm going to discuss this is that I want to show you the relation between sound and movement. And also because this is something you have to deal with, whether as an audio designer or an animator.  In music and sound we use the word loop where in animation we often use the term cycle.

They key thought when creating a seamless loop in audio and animation is that the loop should roughly be like a sine in a graphical approach. I mentioned roughly because it's not necessary to be as curvy as a sine. You could see a sine as a drawn circle, cycle or better yet, a loop in a certain time. We could say we have come full circle!

A sine starts at y=0 and ends at y=0, the origin. The audio example below consists of two sinuses, thus two loops or cycles.The red markers indicate where the loop starts and ends.

Avoiding this story to sound as your monday morning mathclass, I'll just say the more your visual representation of your audio file or animation resembles a sine, the better your loop will be. Thus, if you want a flawless loop, your start and end should have the same y-coordinates and the same angle. The y-coordinate doesn't necessarily need to be 0.  If you do not do this, your animation loop will stutter and in case of your audio loop, it will pop and click.

There are some exceptions in animation where you actually want mirrored angles. A bouncing ball is an example of that.
Here is an examples of bad a loop. (the loop is indicated in blue)

Although the loop start and ends at the same y-value, the loop will pop because the angles are mirrored.
3ds Max users know that if you open the Track View - Curve Editor you will see the graphic representation of your animation.

Here is an example of the movement of a biped pelvis in the animation above. Notice the similarities between this graph and that of the sine audio example.

Of course in real life sound isn’t just one sine and neither do all of we have the same walk cycle. Otherwise everything would be monotonous and boring.  If we look at a more complex audio loop such as this lava audio loop, we can see all of different sorts of sinuses. This gives the sound authenticity.

Importing files

I always save my sounds as wav files, and consider them as my master source files, which I can encode to other formats such as ogg, wma or mp3. I try to avoid saving to mp3 because of the problem, that mp3 encoding places several frames of silence at the start and end of the waveform, which makes looping impossible. The way Unity3d handles audio files is actually quite nice. You can import wav files and choose in Unity3d how it handles its audio files. It also ogg-vorbis compression to keep your final file small.

So this is a small portion of what I do at Xform, I hope haven't dozed you off  to sleep and you can use this in your own work.  
Lets's say goodbye with a seamless loopable track from the forthcoming smash hit
Burnin' Rubber 5.







6 opmerkingen:

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