Playing digitized sound files on the HP48G/GX

[Claudio L.]

(02-08-2018 03:45 PM)sunhp Wrote:  That what I did in WariolandHP 20 years ago : https://www.youtube.com/watch?v=fwXA2Y8d...eIQIIX4OKG

Greyscales + sounds = awesome game

Some 10 years ago I did it for the 50g (written in C).
It was basically using the PWM timers of the CPU to drive the piezo around 100 kHz, varying the pulse width to recreate arbitrary waveforms at a modest 8 khz.
On top of that I coded a 3 channel mixer and an FM synthesizer, you could feed either an arbitrary sound file or just play up to 3 simultaneous notes using synthetic instruments controlled by several parameters.
The sound system ran in the background, using about 6% of the CPU when running at 6 MHz, so you could leave it playing a tune while you kept working on the calculator.
I had a working demo with a piano (actually a synthetic instrument resembling a piano), where each key was a note and you could press up to 3 simultaneously.
The whole thing was a single source file (unremarkably called 'sound.c'), and somehow I lost it. I wanted to use it as the sound driver for newRPL, but I've been looking for it for a few years now. I don't know why or how but it's not in any of my backups.