For some time I was thinking about making for ZX Spectrum an additional sound-card playing BEEPER music without Spectrum's CPU time. If the Z80 mounted on such a card would be faster than 3,5Mhz - it could play even more channels and better envelopes than regular BEEPER.
Sadly I know nothing about soldering, hehe, so I wanted to test this sound in another way.
This 1-bit chiptune has been made on *two* ZX Spectrums 48K (Timex) playing simultanously.
It gave me 6 channels of sound (4 channels of tones and 2 channels of drums). It's totally first test of such idea so I wasn't experiment with stereo this time (it would be possible but more difficult to mix both Spectrums).
Sometimes I used additional channels to make more "wide/deep" 1-bit sound (all channels plays different notes) but sometimes I used them to achieve effects of reverb/delay - then you can hear 2 tones and drums but with additional effects and evnvelopes, as you can notice.
Also I can state that making one half of a chiptune and THEN another half - is a pain in the ass.
This is kind of a new approach to ZX48K music, I hope you like the experiment.
PS: Actually it's possible to get such an effect on one Spectrum - in Tim Follin's music engine - but there is no editor for it so I had to use this funny way.