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The '5th' Amiga audio channel

Amiga audio portia paula waveform sample channel polyphony

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#1 Nebulon OFFLINE  



  • 1,920 posts

Posted Fri Jun 22, 2018 2:11 PM

We all know about OctaMED's 8-channels and how StarDust takes two channels and mux's them together to make a total of 6-note polyphony. 


However, here's a novel way to get a 5th audio channel out of the Amiga by making good use of the (until now) useless composite port:




Additionally, I was doing some reading on the Amiga's audio circuitry and it's pretty interesting. Here's some of the neat things you do:

- Make your own waveforms by drawing them using Audiomaster or some other tracker app.

- Feed raw data into Paula to generate crazy waveforms.

- Play two waveforms over one another to sum them to a single channel.

- Modulate one audio channel with another.

- Use DMA to handle the audio or switch it off and let the CPU take direct control.

- Append one waveform with another in code.

- Overlay all of the channels to create a 14-bit stereo sample playback unit.

- Do AM and FM synthesis with an app like OctaMED.

- Make use of Paula's four included state machines (and send data to them via the CPU or Agnus).

- Increase the sample rate to 57.7 KHz if you have a SuperDenise chip.


It's too bad they didn't up this same design to 16-bit for the release of the AGA machines.


As 8-bit audio chips go though, the sound quality is pretty awesome. A good example of this is the real-time monitoring mode of the DSS8+ cartridge on a machine with a 68030. It almost sounds like a 16-bit stereo sampler.

Also tagged with one or more of these keywords: Amiga, audio, portia, paula, waveform, sample, channel, polyphony

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