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/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 the code, and 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.





*** THE COMMAND LINE



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



     miditones 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>



  The <basefilename> is the base name, without an extension, for the input and

  output files. It can contain directory path information, or not.



  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 by some)



  -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.



  -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 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.



  -sustainlevel=p  The volume level during the sustain phase is p percent of the starting

                   note volume. (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 to 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 covered by the count, if present, are currently undefined

     and should be ignored by players.



 Len Shustek, 2011 to 2019; see the change log.