When a sound is initialized on the MicroKorg, it’s a very simple sound. Reminiscent of the Atari 8 pokey sound created when playing an Advanced Music System II file. Change the OS1 - Wave to Square and the sound seems a little more Atari like.
The one thing that you become aware of is that MicroKorg (or any MIDI synth) will play in perfect pitch where the Atari can only be played at an approximation of the pitch. Therefore, a way of detuning a note to match Atari is required.
It actually works when the calculated pitch bend setting required to detune the MicroKorg is used. KORG8BIT.BAS was written to read the MIDI data sent to the MIDIMax from the Microkorg keyboard. The Atari reads the data and when a NOTEON command is received, it sends a pitch bend setting and then passes the NOTEON command back to the MicroKorg. Because the MicroKorg's MIDI - LOCAL is set to Off, the keyboard output will be sent to the MIDIMax; not directly to the synth. This allows the Atari to control the synth.
To try this out…. Hook the MicroKorg's MIDI OUT and MIDI IN to the Atari MIDI interface MIDI IN and MIDI OUT.
Initialize voice: Shift 3,3
VOICE - VOICE ASSIGN = MON
PITCH - BEND RANGE = 1
PITCH - VIBRATO = 0
OSC1 - WAVE- SQU
MIDI - CHANNEL = 1 (used by program)
MIDI - LOCAL = OFF
MIDI - CLOCK = EXT
Save your sound and global settings if you want.
Boot up your Atari with the M: device autorun.sys file and run KORG8BIT.BAS.
You should be able to play the MicroKorg's keyboard one note at a time (mono) and hear the effect of the detuning program. I thought there was a possibility that BASIC would cause a noticeable delay, but I didn't feel the program needed to be compiled.
The sound is still to clean but to me it sounds a little more like it's POKEY produced.
Got one more step before any time is used recording audio files.
"pokey korg.atr" holds the files created to move this project along. They are in the order they were created and how they were used. .BAS are Atari BASIC and .BTX are LISTed Text files.
DOS.SYS,DUP.SYS - Atari Dos 2.5
AUTORUN.SYS - MIDI Handler M: device
MIDISHELL.BAS - Program lines that are required for using the M: device.
TONES.AMS - ADVANCED MUSIC SYSTEM II was used to create a file to play notes C1 - E6 for
recording into Audiotonic (Audacity). This way the frequency could be derived from the sample and compared with the standard tuning frequency for each note.
NOTES.GMS - A Magic Calc spreadsheet to organize the following data from audio file.
MIDI Note Number: 24 - 88 - AMS note range
Note: C1 to E6
Standard pitch: Hz
Time mark for start of note in audio file
Number of Cycles and Time used to calc Frequency of Atari's pitch or ……
Audiotonic/effect/change pitch option gives the beginning pitch of a selected segment
Pitch Bend Number needed to change Micro Korg pitch to Atari's. It’s a 14 bit number scaled between center and 1 semitone. 8192 = Pitch bend centered. Assumed linear function.
A1TOA5.BAS/.BTX - Tests the notes A1-5 to evaluate Pitch Bend numbers. Sends Pitch Bend Command then NOTEON. Adjusted pitches sounded reasonable.
PWDATA.BAS/.BTX - data Statements for Midi Note number and Pitch bend.
PWDATA2.BAS - program to take PWDATA.BAS and output data statements for the MSB and LSB of a 14bit number. To use with the PITCH BEND MIDI command.
PWDATA2.BTX is the file of the Data statements with MSB and LSB to be ENTERed into a program at lines 31000 to 31050 step 10.
MIDIIN.BAS/.BTX - simple test program to monitor the data stream from MicroKorg. Watching this data helped identify the MIDI Settings. Number 245 Active Sensing pulse needed to be filtered out by the Atari to keep the data buffers from over writing their data. The Pitch Bend Wheel sends out more data then the Atari can handle.
KORG8BIT.BAS/.BTX - This program will accept midi data from the MicroKorg keyboard. Resend it back to the synthesizer with the pitch bend adjustment before the NOTEON command.
NOTE: NOTE is an Atari BASIC reserved word and can not be used as NOTEON Or NOTEOFF. KEYON and KEYOFF variable names were used in place of the MIDI commands.
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