{"id":17083,"date":"2022-08-25T21:36:30","date_gmt":"2022-08-26T01:36:30","guid":{"rendered":"https:\/\/scruss.com\/blog\/?p=17083"},"modified":"2022-08-25T21:36:30","modified_gmt":"2022-08-26T01:36:30","slug":"micropython-midi-mayhem-kinda","status":"publish","type":"post","link":"https:\/\/scruss.com\/blog\/2022\/08\/25\/micropython-midi-mayhem-kinda\/","title":{"rendered":"MicroPython MIDI mayhem (kinda)"},"content":{"rendered":"\n

It pleased me to learn about umidiparser – MIDI file parser for Micropython<\/a>. Could I use my previous adventures in beepy nonsense<\/a> to turn a simple MIDI file into a terrible squeaky rendition of same? You betcha!<\/p>\n\n\n\n

MIDI seems to be absurdly complex. In all the files I looked at, there didn’t seem to be much of a standard in encoding whether the note duration was in the NOTE_ON event or the NOTE_OFF event. Eventually, I managed to fudge a tiny single channel file that had acceptable note durations in the NOTE_OFF events. Here is the file:<\/p>\n\n\n\n

lg2.mid<\/a>Download<\/a><\/div>\n\n\n\n

I used the same setup as before:<\/p>\n\n\n\n

\"Raspberry
piezo between pins 26 and 23<\/figcaption><\/figure>\n\n\n\n

With this code:<\/p>\n\n\n

\n# extremely crude MicroPython MIDI demo\n# MicroPython \/ Raspberry Pi Pico - scruss, 2022-08\n# see https:\/\/github.com\/bixb922\/umidiparser\n\nimport umidiparser\nfrom time import sleep_us\nfrom machine import Pin, PWM\n\n# pin 26 - GP20; just the right distance from GND at pin 23\n#  to use one of those PC beepers with the 4-pin headers\npwm = PWM(Pin(20))\nled = Pin('LED', Pin.OUT)\n\n\ndef play_tone(freq, usec):\n    # play RTTL\/midi notes, also flash onboard LED\n    # original idea thanks to\n    #   https:\/\/github.com\/dhylands\/upy-rtttl\n    print('freq = {:6.1f} usec = {:6.1f}'.format(freq, usec))\n    if freq > 0:\n        pwm.freq(int(freq))       # Set frequency\n        pwm.duty_u16(32767)       # 50% duty cycle\n    led.on()\n    sleep_us(int(0.9 * usec))     # Play for a number of usec\n    pwm.duty_u16(0)               # Stop playing for gap between notes\n    led.off()\n    sleep_us(int(0.1 * usec))     # Pause for a number of usec\n\n\n# map MIDI notes (0-127) to frequencies. Note 69 is 440 Hz ('A4')\nfreqs = [440 * 2**((float(x) - 69) \/ 12) for x in range(128)]\n\nfor event in umidiparser.MidiFile("lg2.mid", reuse_event_object=True):\n    if event.status == umidiparser.NOTE_OFF and event.channel == 0:\n        play_tone(freqs[event.note], event.delta_us)\n\n<\/pre><\/div>\n\n\n
This isn’t be any means a general MIDI parser, but is rather specialized to play monophonic tunes on channel 0. The result is gloriously awful:<\/p>\n\n\n\n