Generate sinewave with keyframed wavelength

Question

hello everybody!
i would like to generate a sinewave with expressions. also i would like to keyframe the wavelenght from the value 20 to the value of 10.
i have this code at the moment:
frequence =(thisComp.layer("streakControl").effect("wavelength")("Slider");
amplitude=10;
x=amplitude*Math.sin(time*frequence);
transform.position+[x,0];
i set the keyframes for the slider "wavelength from 20 to 10 and after effects messes the graph up in the middle of the wavelength-transition.
ist works if i change the "time" expression to Math.PI BUT after the keyframing no values changing and the sin equation returns always the same value so there just a flat line shows up. thats not what i want.
image of the situation with drawn result by AE attached.
any ideas?
greets, clay

Answer 1

to the bottomlayer "streak" is trapcode particular applied. no fancy stuff, just point emitter, directional emitting, no spread,and i subframe interpolation by particular, but with and without interpol. the problem stays.
additionally there is a nullobject "streakcontrol" to manage the position of particular. particular is just linked with je pickwip, no weird thing.
to the nullobject is the code above applied. nothing else.
Well, then it's as I said. You see normal interpolation. Particle properties are assigned at the time of emission and then evaluated over the particle's life cycle and the result you see is 100% correct in that regard. The setup is just unsuitable and you have it backwards. What you want to do would require it just to be the other way around - the emitter moves, particles have zero velocity, when you increase the Y velocity the wavelength expands. It will never be perfectly smooth inbetween, though. If you really must have perfect waves, use the approach Steve described or use efects such as Write-On to generate the lines. If you have Trapcode Form, another option would be audio effectors also modulated with a suitable input tone.
Mylenium