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standard_midi_file_format [2011/10/12 00:08] – created javapimpstandard_midi_file_format [2023/08/18 18:15] (current) – external edit 127.0.0.1
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 +====== Standard MIDI File Format ======
 +
 +//Dustin Caldwell//
 +
 +The standard MIDI file format is a very strange beast. When viewed as a
 +whole, it can be quite overwhelming. Of course, no matter how you look at it,
 +describing a piece of music in enough detail to be able to reproduce it
 +accurately is no small task. So, while complicated, the structure of the midi
 +file format is fairly intuitive when understood. 
 +
 +I must insert a disclaimer here that I am by no means an expert with
 +midi nor midi files. I recently obtained a Gravis UltraSound board for my PC,
 +and upon hearing a few midi files (.MID) thought, "Gee, I'd like to be able to
 +make my own .MID files." Well, many aggravating hours later, I discovered that
 +this was no trivial task. But, I couldn't let a stupid file format stop me.
 +(besides, I once told my wife that computers aren't really that hard to use,
 +and I'd hate to be a hypocrite) So if any errors are found in this
 +information, please let me know and I will fix it. Also, this document's scope
 +does not extend to EVERY type of midi command and EVERY possible file
 +configuration. It is a basic guide that should enable the reader (with a
 +moderate investment in time) to generate a quality midi file.
 +
 +===== 1. Overview =====
 +
 +A midi (.MID) file contains basically 2 things, Header chunks and Track
 +chunks. Section 2 explains the header chunks, and Section 3 explains the track
 +chunks. A midi file contains ONE header chunk describing the file format,
 +etc., and any number of track chunks. A track may be thought of in the same
 +way as a track on a multi-track tape deck. You may assign one track to each
 +voice, each staff, each instrument or whatever you want. 
 +
 +===== 2. Header Chunk =====
 +
 +The header chunk appears at the beginning of the file, and describes the
 +file in three ways. The header chunk always looks like:
 +
 +''4D 54 68 64 00 00 00 06 ff ff nn nn dd dd''
 +
 +The ascii equivalent of the first 4 bytes is MThd. After MThd comes the 4-byte
 +size of the header. This will always be 00 00 00 06, because the actual header
 +information will always be 6 bytes. 
 +
 +''ff ff'' is the file format. There are 3 formats:
 +
 +0 - single-track\\
 +1 - multiple tracks, synchronous\\
 +2 - multiple tracks, asynchronous\\
 +
 +Single track is fairly self-explanatory - one track only. Synchronous multiple
 +tracks means that the tracks will all be vertically synchronous, or in other
 +words, they all start at the same time, and so can represent different parts
 +in one song. Asynchronous multiple tracks do not necessarily start at the same
 +time, and can be completely asynchronous. 
 +
 +''nn nn'' is the number of tracks in the midi file.
 +
 +''dd dd'' is the number of delta-time ticks per quarter note. (More about this
 +later)
 +
 +===== 3. Track Chunks =====
 +
 +The remainder of the file after the header chunk consists of track chunks.
 +Each track has one header and may contain as many midi commands as you like.
 +The header for a track is very similar to the one for the file:
 +
 +''4D 54 72 6B xx xx xx xx''
 +
 +As with the header, the first 4 bytes has an ascii equivalent. This one is
 +MTrk. The 4 bytes after MTrk give the length of the track (not including the
 +track header) in bytes. 
 +
 +Following the header are midi events. These events are identical to the
 +actual data sent and received by MIDI ports on a synth with one addition. A
 +midi event is preceded by a delta-time. A delta time is the number of ticks
 +after which the midi event is to be executed. The number of ticks per quarter
 +note was defined previously in the file header chunk. This delta-time is a
 +variable-length encoded value. This format, while confusing, allows large
 +numbers to use as many bytes as they need, without requiring small numbers to
 +waste bytes by filling with zeros. The number is converted into 7-bit bytes,
 +and the most-significant bit of each byte is 1 except for the last byte of the
 +number, which has a msb of 0. This allows the number to be read one byte at a
 +time, and when you see a msb of 0, you know that it was the last (least
 +significant) byte of the number. According to the MIDI spec, the entire delta-
 +time should be at most 4 bytes long. 
 +
 +Following the delta-time is a midi event. Each midi event (except a
 +running midi event) has a command byte which will always have a msb of 1 (the
 +value will be >= 128). A list of most of these commands is in appendix A. Each
 +command has different parameters and lengths, but the data that follows the
 +command will have a msb of 0 (less than 128). The exception to this is a meta-
 +event, which may contain data with a msb of 1. However, meta-events require a
 +length parameter which alleviates confusion. 
 +
 +One subtlety which can cause confusion is running mode. This is where
 +the actual midi command is omitted, and the last midi command issued is
 +assumed. This means that the midi event will consist of a delta-time and the
 +parameters that would go to the command if it were included. 
 +
 +===== 4. Conclusion =====
 +
 +If this explanation has only served to confuse the issue more, the
 +appendices contain examples which may help clarify the issue. Also, 2
 +utilities and a graphic file should have been included with this document: 
 +
 +DEC.EXE - This utility converts a binary file (like .MID) to a tab-delimited
 +text file containing the decimal equivalents of each byte.
 +
 +REC.EXE - This utility converts a tab-delimited text file of decimal values
 +into a binary file in which each byte corresponds to one of the decimal
 +values.
 +
 +MIDINOTE.PS - This is the postscript form of a page showing note numbers with
 +a keyboard and with the standard grand staff.
 +
 +====== Appendix A ======
 +
 +===== 1. MIDI Event Commands =====
 +
 +Each command byte has 2 parts. The left nybble (4 bits) contains the actual
 +command, and the right nybble contains the midi channel number on which the
 +command will be executed. There are 16 midi channels, and 8 midi commands (the
 +command nybble must have a msb of 1).
 +
 +In the following table, x indicates the midi channel number. Note that all
 +data bytes will be <128 (msb set to 0).
 +
 +<code>
 +Hex      Binary       Data          Description
 +8x       1000xxxx     nn vv         Note off (key is released)
 +                                    nn=note number
 +                                    vv=velocity
 +
 +9x       1001xxxx     nn vv         Note on (key is pressed)
 +                                    nn=note number
 +                                    vv=velocity
 +
 +Ax       1010xxxx     nn vv         Key after-touch
 +                                    nn=note number
 +                                    vv=velocity
 +
 +Bx       1011xxxx     cc vv         Control Change
 +                                    cc=controller number
 +                                    vv=new value
 +
 +Cx       1100xxxx     pp            Program (patch) change
 +                                    pp=new program number
 +
 +Dx       1101xxxx     cc            Channel after-touch
 +                                    cc=channel number
 +
 +Ex       1110xxxx     bb tt         Pitch wheel change (2000H is normal or no
 +                                    change)
 +                                    bb=bottom (least sig) 7 bits of value
 +                                    tt=top (most sig) 7 bits of value
 +</code>
 +                                    
 + The following table lists meta-events which have no midi channel number. They
 +are of the format:
 +
 +''FF xx nn dd''
 +
 +All meta-events start with FF followed by the command (xx), the length, or
 +number of bytes that will contain data (nn), and the actual data (dd).
 +
 +<code>
 +Hex      Binary       Data          Description
 +00       00000000     nn ssss       Sets the track's sequence number.
 +                                    nn=02 (length of 2-byte sequence number)
 +                                    ssss=sequence number
 +
 +01       00000001     nn tt ..      Text event- any text you want.
 +                                    nn=length in bytes of text
 +                                    tt=text characters
 +
 +02       00000010     nn tt ..      Same as text event, but used for
 +                                    copyright info.
 +                                    nn tt=same as text event
 +
 +03       00000011     nn tt ..      Sequence or Track name
 +                                    nn tt=same as text event
 +
 +04       00000100     nn tt ..      Track instrument name
 +                                    nn tt=same as text event
 +
 +05       00000101     nn tt ..      Lyric
 +                                    nn tt=same as text event
 +
 +06       00000110     nn tt ..      Marker
 +                                    nn tt=same as text event
 +
 +07       00000111     nn tt ..      Cue point
 +                                    nn tt=same as text event
 +
 +20 MIDI channel prefix assignment
 +
 +21 has been used, though unofficially, for a MIDI port or cable number. (deprecated)
 +
 +
 +2F       00101111     00            This event must come at the end of each
 +                                    track
 +
 +51       01010001     03 tttttt     Set tempo
 +                                    tttttt=microseconds/quarter note
 +
 +54 SMPTE offset
 +
 +58       01011000     04 nn dd ccbb Time Signature
 +                                    nn=numerator of time sig.
 +                                    dd=denominator of time sig. 2=quarter
 +                                    3=eighth, etc.
 +                                    cc=number of ticks in metronome click
 +                                    bb=number of 32nd notes to the quarter
 +                                    note
 +
 +59       01011001     02 sf mi      Key signature
 +                                    sf=sharps/flats (-7=7 flats, 0=key of C,
 +                                    7=7 sharps)
 +                                    mi=major/minor (0=major, 1=minor)
 +
 +7F       01111111     xx dd ..      Sequencer specific information
 +                                    xx=number of bytes to be sent
 +                                    dd=data
 +</code>
 +
 +The following table lists system messages which control the entire system.
 +These have no midi channel number. (these will generally only apply to
 +controlling a midi keyboard, etc.)
 +
 +<code>
 +Hex      Binary       Data          Description
 +F8       11111000                   Timing clock used when synchronization is
 +                                    required.
 +
 +FA       11111010                   Start current sequence
 +
 +FB       11111011                   Continue a stopped sequence where left
 +                                    off
 +
 +FC       11111100                   Stop a sequence
 +</code>
 +
 +The following table lists the numbers corresponding to notes for use in note 
 +on and note off commands.
 +
 +
 +<code>
 +Octave||                     Note Numbers
 +   #  ||
 +      || C   | C#  | D   | D#  | E   | F   | F#  | G   | G#  | A   | A#  | B
 +-----------------------------------------------------------------------------
 +   0  ||   0 |   1 |   2 |   3 |   4 |   5 |   6 |   7 |   8 |   9 |  10 | 11
 +   1  ||  12 |  13 |  14 |  15 |  16 |  17 |  18 |  19 |  20 |  21 |  22 | 23
 +   2  ||  24 |  25 |  26 |  27 |  28 |  29 |  30 |  31 |  32 |  33 |  34 | 35
 +   3  ||  36 |  37 |  38 |  39 |  40 |  41 |  42 |  43 |  44 |  45 |  46 | 47
 +   4  ||  48 |  49 |  50 |  51 |  52 |  53 |  54 |  55 |  56 |  57 |  58 | 59
 +   5  ||  60 |  61 |  62 |  63 |  64 |  65 |  66 |  67 |  68 |  69 |  70 | 71
 +   6  ||  72 |  73 |  74 |  75 |  76 |  77 |  78 |  79 |  80 |  81 |  82 | 83
 +   7  ||  84 |  85 |  86 |  87 |  88 |  89 |  90 |  91 |  92 |  93 |  94 | 95
 +   8  ||  96 |  97 |  98 |  99 | 100 | 101 | 102 | 103 | 104 | 105 | 106 | 107
 +   9  || 108 | 109 | 110 | 111 | 112 | 113 | 114 | 115 | 116 | 117 | 118 | 119
 +  10  || 120 | 121 | 122 | 123 | 124 | 125 | 126 | 127 |
 +</code>
 +
 +======  BIBLIOGRAPHY ======
 +
 +"MIDI Systems and Control" Francis Rumsey  1990 Focal Press
 +
 +"MIDI and Sound Book for the Atari ST" Bernd Enders and Wolfgang Klemme 1989 M&T Publishing, Inc.
 +
 +MIDI file specs and general MIDI specs were also obtained by sending e-mail to LISTSERV@AUVM.AMERICAN.EDU with the phrase GET MIDISPEC PACKAGE in the message.
 +
 +
 +====== DEC.CPP ======
 +<code cpp>
 +/*  file  dec.cpp
 +
 +by  Dustin Caldwell    (dustin@gse.utah.edu)
 +
 +*/
 +
 +
 +#include <dos.h>
 +#include <stdio.h>
 +#include <stdlib.h>
 +
 +void helpdoc();
 +
 +main()
 +{
 +        FILE *fp;
 +
 +        unsigned char ch, c;
 +
 +        if((fp=fopen(_argv[1], "rb"))==NULL)            /* open file to read */
 +        {
 +                printf("cannot open file %s\n",_argv[1]);
 +                helpdoc();
 +                exit(-1);
 +        }
 +
 +        c=0;
 +        ch=fgetc(fp);
 +
 +        while(!feof(fp))                        /* loop for whole file */
 +        {
 +                printf("%u\t", ch);             /* print every byte's decimal equiv. */
 +                c++;
 +                if(c>8)                                 /* print 8 numbers to a line */
 +                {
 +                        c=0;
 +                        printf("\n");
 +                }
 +
 +                ch=fgetc(fp);
 +        }
 +
 +        fclose(fp);                     /* close up */
 +}
 +
 +void helpdoc()                  /* print help message */
 +{
 +        printf("\n   Binary File Decoder\n\n");
 +
 +        printf("\n Syntax:  dec binary_file_name\n\n");
 +
 +        printf("by Dustin Caldwell  (dustin@gse.utah.edu)\n\n");
 +        printf("This is a filter program that reads a binary file\n");
 +        printf("and prints the decimal equivalent of each byte\n");
 +        printf("tab-separated. This is mostly useful when piped \n");
 +        printf("into another file to be edited manually.  eg:\n\n");
 +        printf("c:\>dec sonata3.mid > son3.txt\n\n");
 +        printf("This will create a file called son3.txt which can\n");
 +        printf("be edited with any ascii editor. \n\n");
 +        printf("(rec.exe may also be useful, as it reencodes the \n");
 +        printf("ascii text file).\n\n");
 +        printf("Have Fun!!\n");
 +}
 +</code>
 +
 +====== REC.CPP ======
 +
 +<code cpp>
 +/*  File  rec.cpp
 +        by Dustin Caldwell   (dustin@gse.utah.edu)
 +*/
 +
 +#include <dos.h>
 +#include <stdio.h>
 +#include <ctype.h>
 +#include <stdlib.h>
 +
 +void helpdoc();
 +
 +main()
 +{
 +        FILE *rfp, *wfp;
 +
 +        unsigned char ch, c;
 +        char s[20];
 +
 +        if((rfp=fopen(_argv[1], "r"))==NULL)                    /* open the read file */
 +        {
 +                printf("cannot open file %s \n",_argv[1]);
 +                helpdoc();
 +                exit(-1);
 +        }
 +
 +        if((wfp=fopen(_argv[2], "wb"))==NULL)                   /* open the write file */
 +        {
 +                printf("cannot open file %s \n",_argv[1]);
 +                helpdoc();
 +                exit(-1);
 +        }
 +
 +        c=0;
 +
 +        ch=fgetc(rfp);
 +
 +        while(!feof(rfp))                       /* loop for whole file */
 +        {
 +
 +                if(isalnum(ch))                 /* only 'see' valid ascii chars */
 +                {
 +                        c=0;
 +                        while(isdigit(ch))      /* only use decimal digits (0-9) */
 +                        {
 +                                s[c]=ch;        /* build a string containing the number */
 +                                c++;
 +                                ch=fgetc(rfp);
 +                        }
 +                        s[c]=NULL;                      /* must have NULL terminator */
 +
 +                        fputc(atoi(s), wfp);/* write the binary equivalent to file */
 +
 +                }
 +
 +                ch=fgetc(rfp);                  /* loop until next number starts */
 +
 +
 +        }
 +
 +        fclose(rfp);                    /* close up */
 +        fclose(wfp);
 +}
 +
 +
 +void helpdoc()          /* print help message */
 +{
 +        printf("\n   Text File Encoder\n\n");
 +
 +        printf("\n Syntax:  rec text_file_name binary_file_name\n\n");
 +
 +        printf("by Dustin Caldwell  (dustin@gse.utah.edu)\n\n");
 +        printf("This is a program that reads an ascii tab-\n");
 +        printf("delimited file and builds a binary file where\n");
 +        printf("each byte of the binary file is one of the decimal\n");
 +        printf("digits in the text file.\n");
 +        printf(" eg:\n\n");
 +        printf("c:\>rec son3.txt son3.mid\n\n");
 +        printf("(This will create a file called son3.mid which is\n");
 +        printf("a valid binary file)\n\n");
 +        printf("(dec.exe may also be useful, as it decodes binary files)\n\n");
 +        printf("Have Fun!!\n");
 +}
 +</code>