Introduction

A number of MOZART aficionados have asked about MOZART's MIDI capability. In the first instance, MOZART was for printing music but its expanding MIDI features are also clearly proving popular. In order to get the best out of playback it is very useful to know a little of the way MIDI works.

The following very basic background information may prove helpful to those with main interests in acoustic music, but who suddenly find that a basic knowledge of MIDI would be useful.  On the other hand, if you're a programmer interested in the real technical details of MIDI file specifications, then one of the clearest references we've found on the net is at
                             http://www.borg.com/~jglatt/tech/midispec.htm.

MIDI concepts

MIDI stands for Musical Instrument Digital Interface and was originally conceived for communication between electronic musical instruments. A MIDI synthesiser, such as the one on your computer's sound card, takes MIDI instructions and synthesises the sounds according to those instructions. The quality of the sound you hear depends entirely on the quality of the synthesiser. (In what follows we talk about the "synthesiser" rather than the "sound card" because Windows can be set to use an external synthesiser if desired, and the MIDI synthesiser is usually just one of a number of components of the sound card.)

MIDI has 16 independent channels on which music can be played simultaneously (although not all sound cards can use all of them). Each MIDI channel can be set to play with a different "voice" (sometimes called a "patch") but more than one channel can be set to the same voice if desired. Some channels (usually 10 and/or 16) are specifically designed for percussion. More on this below. More than one note can be played simultaneously on any channel. (The maximum number is again determined by your synthesiser.)

MIDI files contain a simple sequence of MIDI instructions each of which is time stamped with the amount of time to which must be allowed to elapse since the previous instruction. For example, two of the commonest instructions are note on and note off instructions. These are effectively commands of the form: "start playing the D above middle C on channel 13", and "stop playing the D above middle C on channel 13". The duration of the note you will hear is determined by the time stamp on the second instruction (and any intervening ones). An immediate consequence for MOZART playback is that if you play more than one part on the same channel, then the note off messages from one part can interfere with the other. So, even if you want the same voice on two parts, it can be advisable to use different MIDI channels in order to avoid this interference.

At the most fundamental level there are 128 different possible voices and the time was when every instrument/synthesiser manufacturer had completely different ideas about what sounds 1-128 should be. Nowadays most sound cards confom to the "General MIDI" standard which defines names for each of these. These are the ones listed in MOZART's MidiOptions dialogue. Any MIDI based system allows you to choose which voice is played on which MIDI channel. In addition MOZART allows you to assign a MIDI channel to a part on your printed score.

Percussion

Percussion instruments can be separated into two classes: those of definite, and those of indefinite pitch.   Percussion instruments of definite pitch (eg xylophone, marimba, glockenspiel, vibraphone, tubular bells, timpani,...) are treated by MIDI just as any other instrument.  But MIDI has a special way of treating instruments of indefinite pitch (drums, cymbals, wood blocks, maracas,...) and we shall discuss this here.

MOZART 6 introduces much improved support for percussion instruments of indefinite pitch and we'll mention that below.  For the moment let's look at the underlying features of MIDI.

MIDI synthesisers have one channel which is especially reserved for percussion instruments of indefinite pitch.  On most modern sound cards it is channel 10 (although on some older ones it was often 16).  You do not have to assign a voice to this channel.  The 128 different MIDI pitches, when sent to this channel, just give the sounds of different percussion instruments of indefinite pitch.  (Sometimes they are the sounds of the same instrument but struck differently: for instance three of the "pitches" give the sound of a hi-hat cymbal struck open, struck closed, and operated with the pedal.)

Modern sound cards will conform to the "General MIDI" standard (older ones may not) which defines a specific correspondence between MIDI pitches and percussion instruments on the percussion channel.   The correspondencs is given in a table below.    But to illustrate them more graphically, Jonathan Bryant has kindly supplied the following MOZART example where the parts are all set to channel 10 to get a percussion sound.

The above piece shows all the percussion instruments at their corresponding raw MIDI pitches and was written prior to MOZART 6.  It is still a very valuable illustration, but we note that MOZART 6 introduces much more flexible ways to use percussion of indefinite pitch.

Percussion in MOZART 6

As seen in the above example, you can write a percussion part on a normal stave and just assign the MIDI percussion channel to hear the sounds on play-back.  However the notes are tied to the raw MIDI pitches corresponding to the sounds you wish to produce, and these can be counter intuitive (for example the raw MIDI pitch of the low bongo is higher than that of the high bongo).  To overcome this problem, MOZART 6 introduces a percussion stave on which you can assign any percussion instrument to any line or space on the stave.  Furthermore it groups different sounds made by the same instrument together.  When you play it back, the "pitches" you see on the percussion stave are first converted to the raw MIDI pitch corresponding to the selected instrument and then sent to the synthesiser.  NB you still have to ensure that the part is set to play on the percussion channel!

Appendix: table of raw MIDI pitches according to the General MIDI standard:

The table is written with the higher MIDI pitches at the top.

 

To hear these sounds with MOZART, write a percussion part and use the MidiOptions command to set it on channel 10 or 16. Do not select any particular voice for that channel. When you play the tune, the above percussion sounds will be produced by notes of the appropriate pitches (if your sound card conforms to the General MIDI standard).

Addendum: in the first version of this table, I covered pitches 35-81.   Tim Gill noticed it was incomplete and sent me a more complete table, and so I have extended it up and down.  However, Tim's version is a work of art in itself and is in MOZART format.  I include it here with his permission.  If some of the names in the above table are a little esoteric, then open this file with MOZART and hit the F2 key...