In the ZX Spectrum, the PSG is mixed into stereo because the PSG's three channel output pins ABC can be assigned as left center right using simple resistors.
All ZX Spectrum sound emulators treat PSG as a configurable stereo.
https://documentation.help/AY-3-8910.12-ZX-Spectrum/ay_e0irc.htm
In the ZX Spectrum, the PSG is mixed into stereo because the PSG's three channel output pins ABC can be assigned as left center right using simple resistors.
All ZX Spectrum sound emulators treat PSG as a configurable stereo.
https://documentation.help/AY-3-8910.12-ZX-Spectrum/ay_e0irc.htm