Noise mixer

There is one ingredient behind all four of these: noise, which is just a run of random numbers. Everything else is filtering and modulation — rain is noise with the low end cut away (leave the lows in and it sounds like a fan), a campfire is noise with the high end cut away plus random crackles bursting on top.

What actually makes them feel like weather is slowness. The waves track carries an oscillator that takes 13 seconds to go round once, pushing the filter cutoff and the volume together — one rise and fall is one wave. Stack a second one at 24 seconds and no two waves come out the same. It has to be too slow to notice before the sound reads as alive.

And one more: schedule ahead. Droplets and crackles can't be fired with setTimeout — the timing audibly wobbles. Wake every 120 ms instead and place everything due in the next half second onto the audio clock at exact times. It's the same trick a step sequencer uses.