MIDITONES: Convert a MIDI file into a simple bytestream of notes


  MIDITONES compiles a MIDI music file into a much simplified compact time-ordered stream of
  commands, so that the music can easily be played on a small microcontroller-based synthesizer
  that has only simple tone generators. This is on github at www.github.com/LenShustek/miditones.

  Volume ("velocity") and instrument information in the MIDI file can either be
  discarded or kept. All the tracks are processed and merged into a single time-ordered
  stream of "note on", "note off", "change instrument" and "delay" commands.

  MIDITONES was written for the "Playtune" series of Arduino and Teensy
  microcontroller software synthesizers:

 www.github.com/LenShustek/arduino-playtune
   This original version of Playtune, first released in 2011, uses a separate hardware timer
   for each note to generate a square wave on an output pin. All the pins are then combined
   with a simple resistor network connected to a speaker and/or amplifier. It can only play
   as many simutaneous notes as there are timers. There is no volume modulation.

 www.github.com/LenShustek/Playtune_poll
   This second vesion uses only one hardware timer that interrupts periodically at a fast
   rate, and toggles square waves onto any number of digital output pins.  It also implements
   primitive volume modulation by changing the duty cycle of the square wave. The number of
   simultaneous notes is limited only by the number of output pins and the speed of the processor.

 www.github.com/LenShustek/Playtune_samp
    The third version also uses only one hardware timer interrupting frequently, but
    uses the hardware digital-to-analog converter on high-performance microntrollers like
    the Teensy to generate an analog wave that is the sum of stored samples of sounds for
    many different instruments. The samples are scaled to the right frequency and volume,
    and any number of instrument samples can be used and mapped to MIDI patches. The sound
    quality is much better, although not in league with real synthesizers. It currently
    only supports Teensy boards.

 www.github.com/LenShustek/Playtune_synth
   The fourth version is an audio object for the PJRC Audio Library.
      https://www.pjrc.com/teensy/td_libs_Audio.html
   It allows up to 16 simultaneous sound generators that are internally mixed, at
   the appropriate volume, to produce one monophonic audio stream.
   Sounds are created from sampled one-cycle waveforms for any number of instruments,
   each with its own attack-hold-decay-sustain-release envelope. Percussion sounds
   (from MIDI channel 10) are generated from longer sampled waveforms of a complete
   instrument strike. Each generator's volume is independently adjusted according to
   the MIDI velocity of the note being played before all channels are mixed.

 www.github.com/LenShustek/Playtune_Teensy
   The fifth version is for the Teensy 3.1/3.2, and uses the four Periodic Interval
   Timers in the Cortex M4 processor to support up to 4 simultaneous notes.
   It uses less CPU time than the polling version, but is limited to 4 notes at a time.
   (This was written to experiment with multi-channel multi-Tesla Coil music playing,
   where I use Flexible Timer Module FTM0 for generating precise one-shot pulses.
   But I ultimately switched to the polling version to play more simultaneous notes.)

 www.github.com/LenShustek/ATtiny-playtune
   This is a much simplified version that fits, with a small song, into an ATtiny
   processor with only 4K of flash memory. It also using polling with only one timer,
   and avoids multiplication or division at runtime for speed. It was written
   for the Evil Mad Scientist menorah kit:
   https://www.evilmadscientist.com/2009/new-led-hanukkah-menorah-kit/
   https://forum.evilmadscientist.com/discussion/263/making-the-menorah-play-music
   (Imagine what you can do with the $1 8-pin ATtiny85 with a whopping 8K!)

 MIDITONES may also prove useful for other simple music synthesizers. There are
 various forks of this code, and of the Playtune players, on Githib.

 *** THE PROGRAM

  MIDITONES is written in standard ANSI C and is meant to be executed from the
  command line.  There is no GUI interface.

  The output can be either a C-language source code fragment that initializes an
  array with the command bytestream, or a binary file with the bytestream itself.

  The MIDI file format is complicated, and this has not been tested on all of its
  variations.  In particular we have tested only format type "1", which seems
  to be what most of them are.  Let me know if you find MIDI files that it
  won't digest and I'll see if I can fix it.

  There is a companion program in the same repository called Miditones_scroll
  that can convert the bytestream generated by MIDITONES into a piano-player
  like listing for debugging or annotation. See the documentation near the
  top of its source code.
  
  Additional binaries have been compiled and tested on arch linux, with the files
  having an additional _linux appended to their name; please contact @Oman395 on
  github if your distrobution has issues running them.


*** THE COMMAND LINE

  To convert a MIDI file called "chopin.mid" into a command bytestream, execute

     miditones chopin
     
  Or on linux, execute
  
    ./miditones_linux chopin

  It will create a file in the same directory called "chopin.c" which contains
  the C-language statement to intiialize an array called "score" with the bytestream.


  The general form for command line execution is this:

     miditones  <options>  <basefilename>
     
  Or on linux:
      
      ./miditones_linux <options> <basefilename>

  The <basefilename> is the base name, without an extension, for the input and
  output files. It can contain directory path information, or not.

  If the user specifies the full .mid filename, the .mid or .MID extension
  will be dropped and the remaining name will be used as <basefilename>.

  The input file is <basefilename>.mid, and the output filename(s)
  are the base file name with .c, .h, .bin, and/or .log extensions.


  The following commonly-used command-line options can be specified:

  -v    Add velocity (volume) information to the output bytestream

  -i    Add instrument change commands to the output bytestream

  -pt   Translate notes in the MIDI percussion track to note numbers 128..255
        and assign them to a tone generator as usual.

  -d    Generate a self-describing file header that says which optional bytestream
        fields are present. This is highly recommended if you are using later
        Playtune players that can check the header to know what data to expect.

  -b    Generate a binary file with the name <basefilename>.bin, instead of a
        C-language source file with the name <basefilename>.c.

  -t=n  Generate the bytestream so that at most "n" tone generators are used.
        The default is 6 tone generators, and the maximum is 16. The program
        will report how many notes had to be discarded because there weren't
        enough tone generators.

 The best combination of options to use with the later Playtune music players is:
        -v -i -pt -d

 The following are lesser-used command-line options:

  -c=n  Only process the channel numbers whose bits are on in the number "n".
        For example, -c3 means "only process channels 0 and 1". In addition to
        decimal, "n" can be also specified in hex using a 0x prefix.

  -dp   Generate Arduino IDE-dependent C code that uses PROGMEM for the bytestream.

  -k=n  Change the musical key of the output by n chromatic notes.
        -k=-12 goes one octave down, -k=12 goes one octave up, etc.

  -lp   Log input file parsing information to the <basefilename>.log file

  -lg   Log output bytestream generation information to the <basefilename>.log file

  -n=x  Put about "x" items on each line of the C file output

  -p    Only parse the MIDI file, and don't generate an output file.
        Tracks are processed sequentially instead of being merged into chronological
        order. This is mostly useful for debugging MIDI file parsing problems.

  -pi   Ignore notes in the MIDI percussion track 9 (also called 10 in some documents)

  -r    Terminate the output file with a "restart" command instead of a "stop" command.

  -sn   Use bytestream generation strategy "n". Two are currently implemented:
          1:favor track 1 notes instead of all tracks equally
          2:try to keep each track to its own tone generator

  -h   Give command-line help.

  -showskipped     Display information to the console about each note that had to be
                   skipped because there weren't enough tone generators.

  -noduplicates    Remove identical notes played on identical instruments for the same time
                   that come from different tracks. This can reduce the number of tone 
                   generators needed, and make the file smaller.

  -delaymin=x      Don't generate delays less than x milliseconds long, to reduce the number
                   of "delay" commands and thus make the bytestream smaller, at the expense of
                   moving notes slightly. The deficits are accumulated and eventually used,
                   so that there is no loss of synchronization in the long term.
                   The default is 0, which means note timing is exact to the millisecond.

  -releasetime=x   Stop each note x milliseconds before it is supposed to end. This results
                   in better sound separation between notes. It might also allow more notes to
                   be played with fewer tone generators, since there could be fewer
                   simultaneous notes playing.

  -notemin=x       The releasetime notwithstanding, don't let the resulting note be reduced
                   to smaller than x milliseconds. Making releasetime very large and notemin
                   small results in staccato sounds.

  -attacktime=x    The high-volume attack phase of a note lasts x milliseconds, after which
                   the lower-volume sustain phase begins, unless the release time makes it
                   too short. (Only valid with -v.)

  -attacknotemax=x Notes larger than x milliseconds won't have the attack/sustain profile
                   applied. That allows sustained organ-like pedaling. (Only valid with -v.)

  -sustainlevel=p  The volume level during the sustain phase is p percent of the starting
                   note volume. The default is 50. (Only valid with -v.)

  -scorename       Use <basefilename> as the name of the score in the generated C code
                   instead of "score", and name the file <basefilename>.h instead of
                   <basefilenam>.c. That allows multiple scores to be directly #included
                   into an Arduino .ino file without modification.

  Note that for backwards compatibility and easier batch-file processing, the equal sign
  for specifying an option's numeric value may be omitted. Also, numeric values may be
  specified in hex as 0xhhhh.

*** THE SCORE BYTESTREAM

  The generated bytestream is a series of commands that turn notes on and off,
  change instruments, and request a delay until the next event time.
  Here are the details, with numbers shown in hexadecimal.

  If the high-order bit of the byte is 1, then it is one of the following commands,
  where the two characters are a hex representation of one byte:

    9t nn [vv]
           Start playing note nn on tone generator t, replacing any previous note.
           Generators are numbered starting with 0. The note numbers are the MIDI
           numbers for the chromatic scale, with decimal 69 being Middle A (440 Hz).
           If the -v option was given, the third byte specifies the note volume.

    8t     Stop playing the note on tone generator t.

    Ct ii  Change tone generator t to play instrument ii from now on. This will
           only be generated if the -i option was given.

    F0     End of score; stop playing.

    E0     End of score, but start playing again from the beginning. This is
           generated by the -r option.

  If the high-order bit of the byte is 0, it is a command to delay for a while until
  the next note change.  The other 7 bits and the 8 bits of the following byte are
  interpreted as a 15-bit big-endian integer that is the number of milliseconds to
  wait before processing the next command.  For example,

     07 D0

  would cause a delay of 0x07d0 = 2000 decimal millisconds, or 2 seconds.  Any tones
  that were playing before the delay command will continue to play.

  If the -d option is specified, the bytestream begins with a little header that tells
  what optional information will be in the data. This makes the file more self-describing,
  and allows music players to adapt to different kinds of files. The later Playtune
  players do that. The header looks like this:

    'Pt'   Two ascii characters that signal the presence of the header
     nn    The length (in one byte) of the entire header, 6..255
     ff1   A byte of flag bits, three of which are currently defined:
               80 volume information is present
               40 instrument change information is present
               20 translated percussion notes are present
     ff2    Another byte of flags, currently undefined
     tt     The number (in one byte) of tone generators actually used in this music.

     Any subsequent header bytes included in the length are currently undefined
     and should be ignored by players.

  Len Shustek, 2011 to 2021; see the change log.