BBC sampled sound discs: smooth streaming, 50Hz oscilloscope

[scarybeasts]

Hi,

I've made a couple of BBC sampled sound discs. Emulate online:

https://bbc.godbolt.org/?disc=https://r ... k&autoboot

https://bbc.godbolt.org/?disc=https://r ... k&autoboot

These are a bit like the ones you got back in the day except they start immediately and continuously stream from the disc asynchronously without gaps. There is also a 50Hz oscilloscope view squeezed into the spare cycles.

There are a few internet resources and threads regarding how the SN76489 is coaxed into making sampled sound. But I found some of them a bit hand-wavey so I wrote a blog on how it works: https://scarybeastsecurity.blogspot.com ... 76489.html

This came out of an investigation into an asynchronous disc loading library that can autodetect 8271 vs. 1770 and drive them directly. It's called quicdisc and hosted here: https://github.com/scarybeasts/misc


Cheers
Chris

[tricky]

Nice one Chris and great little article.
I didn't realise that that encoder offset the samples.

[Diminished]

Very cool!

Great stuff as always. Impressive that you can get entire songs on a disc.

It's interesting that it wouldn't work at all if the chip implemented its attenuation symmetrically!

[alexandersmith]

Did you know you made it to hackaday?

https://hackaday.com/2020/06/05/how-did ... ound-chip/

Congrats!