Long time ago I inserted a SpecDrum version of playzb4().
It is a WavePlay function originally created for the Commodore SID working on 4bit samples.
The SpecDrum is rather uncommon and I preferred to leave it in source code form only. Now I discovered that the Scorpion and the Pentagon had their way to output sound to an 8bit Covox interface and I decided to simply extend this same function rather than creating many special cases, if an interest will arise we can get more accurate (in example I'm sure that a Covox style interface will work on many other parallel interfaces, like the Opus Discovery one).
In the meanwhile this the way to build a demo valid for Scorpion, Pentagon and SpecDrum interface, IN 48K MODE it won't crash:
zcc +zx -lndos -create-app /z88dk/examples/sound/bit4.c /z88dk/libsrc/target/zx/specdrum/playzb4.asm