getting sound effects out of the beeper

[catmeows]

Yes, you can draw behind beam. And instead of using floating bus (which do not work on every model/clone) just use wait loop. You can replace wait loop by sound routine but 15K ticks is too little to produce anything but farts and few notes. You may want to make sound loop longer, say 20K or 25K to get slightly better sound. Then you start drawing things from top to bottom.

[DoctorRad]

Cobra on the 48k spectrum has an amazing sound routine, but I can find nothing online explaining even how to make these 1bit samples or what it might be doing to make the sound:

My suggestion would be to hook a Spectrum or emulator up to something which allows you to record a WAV of the sound, and then look at the waveform in a soundfile editor like Audacity. You should be able to see the transitions between 1 and 0 for a given sound effect, then it's up to you to work out how to implement the CPU timing to produce that pattern of transitions around the rest of your code.

As an aside, I remember reading BITD that Manic Miner wasn't interrupt driven, but the beeps for the music and jumping were interlaced with sprite movements. I believe this is why the game runs slightly faster if you turn off the music.