The improbable music of the ZX Spectrum's one-bit speaker

Even for 1982, the Sinclair ZX Spectrum had poor sound: a piezoelectric speaker that could beep. But you can do a lot with a single bit if you turn it on and off really fast. Michael Martin's Bumbershoot Software site has done some fascinating deep dives into several long-gone computer systems, including a whole series on implementing a game on the ZX Spectrum, starting in May with Giving the ZX Spectrum a Fair Shake.