This is great! Didn't know what the ZX Spectrum was, and this was a nice little video. One interesting thing is, to me at least - a musician, is that the Spectrums are not necessarily in tune; the first one playing the melody seems sharper than all the others. I wonder if the devs were aware of this, and tried fixing it?..
That's probably down to the 128K Spectrums having a slightly faster clock speed than the original 16/48K model (3.5469MHz versus 3.5 exactly). I knew this would cause the timings to drift (hence the need for the RasPi to provide a time source) but I overlooked the effect this would have on pitch... (On the other hand - since the BEEP routine was being called from BASIC, adding in a pitch adjustment calculation may we…
Are the internals of the project documented anywhere? I'd love to see how you did the synchronisation (and why you had to use that interloping Acornesque Pi instead of another Spectrum as conductor - was it a file server as well?) and see some code...
A purist would doubtless sigh after a Spectrum only network using Interface 1's ZX Net and Microdrives, but (a) life is too short (b) I doubt anyone else would care and (c) I am not that man. :)