[Koby Goldberg]

Try this:
use the delay paremether as the starting time for the decay.

veloc = 7;
amplitude = 80;
decay = 0.7;
delay = 2;

sin = amplitude*Math.sin(veloc*time);
(time < delay) ? sin : sin/Math.exp(decay*(time-delay))

Koby.

[Koby Goldberg]

What you’ve tried is indeed incorrect for such a motion.
It’s a bit too complicated to explain.
Try this instead:

sum = 0;
dt = thisComp.frameDuration;
f = thisComp.layer("Null 1").effect("time_variable")("Slider");
for (t=inPoint; t < time; t+=dt) {
sum += f.valueAtTime(t);
}
50*Math.sin(sum)*dt

Koby.

[Koby Goldberg]

Check out this post on AEnhancers.com
https://aenhancers.com/viewtopic.php?f=3&t=1083
perhaps it could help you.

Koby.

[Koby Goldberg]

You could also use the inPoint of the layer to choose the desired delay, in a way that if you move the layer in timeline to start later, the effect would start later.

In order to do this, you could use Dan’s last expressions and just replace the delay to this:

delay = inPoint;

Koby.

[Koby Goldberg]

Hi Eric,
No, this is not the same.
SIN(X) is also negative (in case pi

[Koby Goldberg]

Or this

period = 3;
t = time;
50*(1 – Math.cos(t / period * Math.PI))

(which will yield almost the same result as Dan’s expression, but i think will render faster 🙂 )

Koby.

[Koby Goldberg]

Eric’s idea is really nice and simple.
If you want to change the time that the opacity rises from 0 to 100 to a specific duration value, use the following expression:

duration = 3;
Math.abs(Math.sin(time/duration*Math.PI)*100)

if you insist on linear opacity and not SIN opacity, you could use the next expression:

duration = 3;
T = Math.round(duration/thisComp.frameDuration);
t = Math.round(time/thisComp.frameDuration);
100*( 1 - Math.abs(t%(2*T) - T)/T )

Koby.

[Koby Goldberg]

Thanks Eddie,
But that’s not what I meant…

CS3 had a new button just above the timeline called: “disable or enable previews” which disabled the RED line above the timeline in areas that were not rendered. Pressing this button disabled the rendering, (and the RED line would turn into WHITE line) and thus saved memory and hard drive space. Just after ending the project, you would re-enable the preview render (by pressing this button again) and would make a preview once. (Each preview render you make, by pressing ENTER, saves big video files to your hard drive, which are not being erased until you erase them yourself. so all those files are being saved, and Premiere searches for them for rendered areas, to display the video better when you preview it. this searching task takes memory and cpu power).
And the problem is that I can’t find that button in CS4. Maybe it was moved elsewhere…?