[info/bug?][mtx] 1-bit sound support?

[Fabrizio-Caruso]

I have not understand if 1-bit sound is supposed to work in the MTX target as the doc is ambiguous about it (it is shown in the table but not in the target doc: https://github.com/z88dk/z88dk/wiki/Platform---Memotech-MTX)

Anyway, if I try it I get a continuous sound. So it seems broken.

[suborb]

This is the old sn76489 issue. In theory there's a 1 bit emulation layer over the sound chip. In practice it only works for a very few machines.

As a result, it's marked as not present in features.h: https://github.com/z88dk/z88dk/blob/master/include/features.h#L2223 - I'll update the table.

[Fabrizio-Caruso]

I see:

__HAVE_PSG_SN76489 1

Does it mean that I should be able to produce some sounds with the PSG_SN76489 specific API's ?

I have not succeeded so far. I can produce a minimal example but I am not sure I am using the API's correctly.

[zx70]

As said elsewhere already I'm trying to sort the older sound libraries.

The current library for the SN76489 is automatically inerithing the whole 1bit code, and now also the 4bit wav player. The underlying mechanism relies on an undocumented feature of the PSG chips (it is valid also for some of the YM chips), the oscillators, basing on some article available on Internet, can be stopped keeping the output "active low". Then, by raising and lowering the volume, an analog-like output should be possible. We have two main question marks, though:

• Are ALL the chip variants behaving like this ? Is this behavior always available or it depends on the way the chip is wired ?
• Are the emulators capable of recreating the undocumented feature properly ?

The code is in, but we can't trust the emulators to confirm it works, nor a silent output on an emulator means it wouldn't play properly on the real machine.