Using MidiJoy on the Atari
When you have connected the interface to both the Mac/PC and the Atari has booted into MidiJoy, you are ready to play music on your Atari by sending Midi notes from the Mac/PC to the interface. A simple equalizer will give you visible feedback as well.
All incoming data will be adjusted correctly to the Atari note table and then played immediately. As far as possible, proper scales are used also in distortion modes 2 and 12. Pressing the SPACE key switches between two different scales in mode 12.
Incoming Midi data is expected on Midi channel 1 to 4. These are then played through the corresponding sound channels on the Atari. Midi channel 1 is special: here, up to four voices are being split up automatically to unused sound channels on the Atari. This enables playing multi-chords with up to four voices in real time, for example via a Midi keyboard connected to the Mac/PC. Five or more voices will overwrite the last used channel.
You may use your own ADSR envelopes (see next post) during live playback by activating one of them by pressing keys 1 to 8. Envelope data needs to be loaded prior to starting MidiJoy (e.g. via DOS).
Keys O to I control the eight bits of the AUDCTL register. This enables making live use of all POKEY features such as filters, 16-bit voices or frequency changes. Like with sound programming in general, only certain combinations make sense. For example, it is advisable to set POKEY's frequency to 1.77 MHz (bits 5 and 6) when using 16-bit voices (bits 3 and 4 respectively).
Individual channels can use different distortions (AUDC1-4). These can be set using keys A to D, F to H, Z to C and V to N. The status of each bit is displayed on the screen.
The tabulator key starts and stops the recording mode. Pressing RETURN resets all recordings, for example to start anew.
While recording, all incoming note data is saved to RAM and can then be played back using the P key (after recording is stopped). A counter displays the memory area used by the recording. This area can afterwards be saved for later use by jumping into DOS (J key) and use the "Save Binary File" function there. This of course requires that MidiJoy has been started with DOS in the background - simply booting the executable from a game DOS or SD-card will not allow you to save your recordings!
Take note that when you enter recording more, also the silence until the first note value comes in is recorded. So if you press TAB and only then start to boot your Mac/PC, you'll have a long(er) silence at the beginning when you later start to play the recording.