Hi there,
So I'm relatively new to After Effects but I've been able to understand a lot of how it works. I'm trying to add a new effect in my music videos by increasing the particles per sec every time there is bass. I'll add a link to a video if i can. The best example is at 1:30. The particles seem to increase with the bass but when I try doing it with sound keys it just resets to 0 particles per sec until the bass then it goes to 150 and back to 0 after the bass stops.
Basically the video that I linked appears to keep the particles consistent with every kick drum and bass, but with my videos it looks like there are less particles due to the bass moving them faster. How do you think they got there particle effect like that?
Sorry if this is confusing. I can give more info if needed 
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Replies
You have to start by understanding how particle systems work. There is an emitter which has a defined size and position, there is the particle, and then there is particle velocity. Once the particle has been emitted it is moving with a certain speed. You can animate gravity, wind, but you cannot increase the number of particles after they have left the emitter. Once a particle is emitted and started down it's path you can only influence that path, the size and the color of the particle over its lifetime.
Start by playing with the controls and some keyframes to figure out what approach you want to take before you try and use Sound Keys to control the animation. Just poking around with some values and some properties and running previews is pretty much a waste of time.
Something like this would get you started on seeing how animating the number of particles per second makes them behave.
The sets of 3 keyframes go from zero and 1000 and then back to zero. The size over time is animated by the curve you see in the effects control panel. Every time there is a group of 3 keyframes a little explosion happens, the particles get bigger very quickly then the size goes down. The results look something like fireworks going off. There are remnants of the first explosion on the outside, then the second explosion a little bigger and closer to the emitter, then the third explosion is just getting started.
The visual perception of motion is delayed compared with the keyframes so when you are using sound keys to generate the keyframes you'll have to shift some things around in time so the movement matches the beat.
Your example video does not show an increase in the number of particles, it shows a change in speed towards the camera. One way to do that using Particular would be to animate the speed of the wind in the z direction with the default camera. Here's how you would set that up to experiment with the range of values you would need sound keys to generate. Size over time may help keep the particles from getting too big as they approach the camera.
In this case the groups of 3 keyframes for Wind Z go from zero to -6000. Your values depend on how much you want the speed to increase.
Once you figure out how to move the particles in their 3D space you can figure out the range of values you need to set to get the movement you want.
Particular is an incredibly complex and difficult to understand particle system. It would really help you to spend some serious time on the Red Giant site going over the Particular tutorials so you can figure out how the knobs work. I spend a couple of hours over there every time they release a new version so I can more efficiently fiddle with the knobs.
I would also hope that you try and put a little more thought and creativity into your music videos than I saw in the linked example. Anybody can do purely mechanical effects but they don't help tell the story of the music. The creativity and cool factor can very quickly fall to zero.
I only use sound keys for 3 different particle effects at the most. I tried altering some of the particle settings but as soon as there's a kick drum or there's bass the particle density decreases due to most of the particles being moved off screen by wind z. I think i'll have to change the particles/sec every time there is a kick drum or prolonged bass otherwise I'm left with barely any particles on screen until a few seconds later when more particles are emitted.
Thank you for your help though
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