This one doesn’t use the CPX speaker, the audio output from the external mixer circuit is being amplified. It’s also shown on a Telequipment S51B oscilloscope (the one with the broken trigger function).
Then a bit more about the complexities involved:
I’ve realised the youngsters may not understand the origins of this arrangement and the challenges of the rendition on the 1 bit sound of the ZX Spectrum. Some background:
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