Creating changing background with trapcode particular and sound keys

[Kalleheikki Kannisto]

So you want the entire background to be redrawn on a bass drum hit?

That would be something like this.

1) Emit all particles at once, during one frame, at the beginning of each second, with a life of 1/25 of a second. So, if you have a frame rate of 25 and want 25 particles, that would be 25×25 = 625particles per second. This way you will have a comp where the background changes every frame. Precomp that moving all attributes.

You might want to consider at this point how many different background you actually need. Every second of footage gives you 25 different backgrounds. I would settle for 100, which would be 4 seconds — adjust precomp length accordingly.

2) Prerender that precomp. (You cannot time remap a Particular layer.)

3) Generate SoundKeys trigger output for your bass. Use 0-1 range and “instant” fall off.

4) Generate second output with same range with trigger set to 0-1 but with “none/integrate” fall-off. This way every bass hit will add to the previous value.

5) Time Remap the prerendered background footage layer. The following time remap code will use these two Soundkeys outputs but ignore cases where the output stays at 1 on consecutive frames. Also, if you’ve made the footage shorter, say 4 seconds, you will need an expression that gives you the modulus (remainder of division) of 4. That would be:

if(thisComp.layer("SoundKeys").effect("Sound Keys")("Output 1")==1){
n=time;
while (n

Leave out the %4 if you don't need to circulate in the first four seconds.

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Note: Time remapping a layer and then applying an effect to the same layer will NOT time remap the effect. The effect needs to be inside the time remapped precomp, not applied at the same level.

Kalleheikki Kannisto
Senior Graphic Designer

[Tyler Lynn]

Hi,
First of all, thanks SO much for the reply! I’ve been trying to do this for a week and finally I’m coming close. I did everything you said, but the background particles still change twice each bass hit, and the background reverts to frame 1 between each bass hit. Here’s a link to the project file if you could take a look. “Main” is where I’ve been trying to put this together, and Sprites _4mov is layer I want to effect.
Thank you !

https://drive.google.com/open?id=1i6ptS8EoHp-p23ClHZ6ftImZ_VA1Q_oW

As a sidenote, could I alternatively use soundkeys with a none/integrate falloff, then use an expression that ignores output of 1 on consecutive frames, then link that to particular’s random seed? That way with each hit it counts up one random seed? To do that though, I think I’d also need to create a particular that has particles present at a given frame but doesn’t produce any additional particles.

[Kalleheikki Kannisto]

Hi, appears that the SoundKeys effect is not set up exactly in the described manner. The Output 1 and 2 ranges are not at the same exact coordinates and the output values not in the 0-1 range. If you fix those and update (click “Apply” in SoundKeys), you should get there.

Kalleheikki Kannisto
Senior Graphic Designer

[Tyler Lynn]

Hi, that did it. Thanks so much for the help! I almost cried when I saw it finally working.