MIDI signals, also called messages, can be sorted into two groups. In one group the MIDI signals are related to one channel, in the other they are not; the former are referred to as channel messages, the latter as system messages. The channel messages are also divided into voice messages – which controls the voices in the devices – and mode messages – they are used to control the operating modes. The system messages are composed of common messages – they are responsible for tuning and selecting songs and real time messages – they are responsible, among other things, for instructions on start and stop and also exclusive messages, in which nearly all data of two devices can be sent and received.
MIDI channel messages
Let’s get back to the channel messages, the channel-related MIDI commands. The most important is the note-on command. This message is assigned to a note number. Each note, from the lowest to the highest, receives a number for each semitone step. The message also indicates the volume in which the note should be played. In English, this is referred to as velocity, which refers to the touch dynamics of a keyboard. Values from 0 to 127 are possible for the velocity parameter. If the instrument is missing one, the default (mean) 64 is set. The note-on message is not only needed to control a sound, but it is also used for further tasks. If a note is to be muted, the note-off command is given, which includes the number of the note and the velocity. If a note-on command with velocity equal to zero were selected, it would be equivalent to a note-off command because the receiver would have to be regard as such. Another command refers to the so-called aftertouch in which two types are distinguished: the channel aftertouch and the polyphonic aftertouch. The latter is also known as polyphonic key pressure. To modulate a sound after playing, the aftertouch does valuable service. With polyphonic key pressure it is possible to edit every single note; on the aftertouch channel, on the other hand, the entire channel is affected. The whole thing can be done in different ways, depending on the instrument. To influence the pitch of a channel, a pitch bend is used. All sounds from a MIDI channel can be changed. The command is usually triggered by means of a wheel, which can be rotated, causing sliding modulations. Usually it is built to the left of the keyboard. To conclude the MIDI versions, reference is still made to the General-MIDI standard, which was published in late 1991. Each sound receives its own program number, which ranges from 1 to 128; they are valid for all MIDI channels, with the exception of MIDI channel 10, which is for drum sounds. It contains 47 sound examples of the percussive kind, starting with the acoustic bass drum up to the open triangle. The program numbers for the normal sounds start with the sound of concert grand piano and end with a sound rifle shot. Perhaps Prokofiev’s “Peter and the Wolf” had made sure that this rather unusual sound got its own program number. In the musical fairytale from ancient Russia, however, the rifle shots were still triggered by timpani.
The last part
Did you like this article about the midi signals and channels? Share it in your favorite social media and tell us your opinion about the midi signals! Do you want to get more information about the synthesizer? Click here to read the last part of the synthesizer series. The last part will tell you more about the synthesis.