BTW, slowing down idm and similar busy electronic music, in the manner of vinyl, is quite solid entertainment. Aphex Twin is known for this, so much so that RDJ admitted he knows about this and suggested that ‘RDJ Album’ could be listened at 33 RPM to obtain an album of ‘standard’ 45 minutes: https://www.youtube.com/watch?v=aWqf17mUyoQ

You need to take care to properly slow down the audio, though, with corresponding pitch shift down. Not ‘stretching’ it keeping the pitch constant.

Apparently the genre of New Beat stemmed in large part from DJs playing rave records at wrong tempos: https://www.youtube.com/watch?v=5yBvP3616Wc (see also https://www.youtube.com/watch?v=4XUipCxjmmw).

I've also had similarly splendid results with slowing down hard house (specifically my favorite compilation Insomnia Vol.2 from Tidy Trax). It turned into proper house with lotsa relaxed steady drive but much more engaging sound.

On your own machine, both workstation and telephone, VLC can alter the playing speed with good quality and proper pitch shift (or with no shift!). For batch converting, `sox` is a good choice—ffmpeg botches the sound for some reason.