Another approach; very simple but imperfect, would be to sample the spectrum with a fast ADC at, say, 100MHz; collect (say) 1 ms of data, and replay it at 100kHz (when it will last 1 second).
The tricky bit is to decide what to do at the start/end of this sampled block; if you sample 1ms every 0.5s you would always have 2 seconds worth of audio on the go simultaneously; smoothly fade the older one down as you fade the newer one up.
This could be an interesting experiment as well as a bizarre form of electronic music; John Cage would probably approve!