But clearly this is okay but it's not that interesting in the sense that

we are manipulating not just the duration but the whole quality of the sound.

So more interestingly,

when we talk about time scaling what we normally are referring is to be able to

change the duration of the sound without changing the quality

of the sound without changing the frequencies that are present in the sound.

And within the density there is a few

algorithms into that the most sophisticated one that I know of.

He's this one that says is sliding time scale pitch shift, okay?

And this algorithm performs both tempo change, or time change, and pitch change.

And it uses a sinusoidal model.

In fact, it uses sinusoidal model very similar to the one that we have

been presenting in class.

And you can of course look at the code of this algorithm

on the Audacity website, you have access to the source code of that,

the major difference which is an important one is that this sinusoidal model

is based on a sub bond type of processing.

So it does sign sort of modeling while it's splitting the whole sound

in octaves and modeling every octave with a different analysis, synthesis approach.

So, the quality is a little bit better than what we can do in the algorithm that

we have been developing in class.

So let's listen to that and it easily can be controlled in time,

so here for example the control of this algorithm can be done in a way that we

have an initial tempo change as a percentage, and a final tempo change.

So, for example, what we can do is start slower, so lets say,

okay lets start with lets say, 20% or

22% slower and let's finish by speeding up.

So let's, for example, end up with 30% speed increase.

Okay, but remember these we are not changing the reading of the samples,

the time domain samples, this is done.

Using the sinusoidal model.

So therefore, re-synthesizing the sinusoids but

a different speech while maintaining the pitch of the sinusoids.

So, let's analyze this, it is quite fast.

In fact, it's a very efficient algorithm implementing C.

So now, we are done and we have change the duration,

well it's a time varying duration so let's listen to that.

>> [MUSIC]

Okay. So, we have the time duration and

clearly, the peak or the frequencies have not changed,

the sound has changed in duration, has speed up, the tempo has increased but,

not the frequencies and that's a pretty good algorithm.

There's some more sophisticated ones, but

this is pretty decent one, that can perform good time scaling algorithms.

So, now let's go to our the own implementation.

So, let's go to the GUI of transformations that we have.

And let's go to the sign model.