9_MIDI_code

9_MIDI_code - MIDI Code Juan P Bello MIDI Code: the message...

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MIDI Code Juan P Bello
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MIDI Code: the message format 2 types of MIDI message bytes: the status byte and the data byte Status bytes always begin with 1, and data bytes with 0. That leaves only 7 bits per byte to represent the message (128 possible values). MIDI messages begin with the status byte, where 3 bits ( sss ) are used to denote the type of message, and 4 bits ( nnnn ) to denote the channel number to which the message apply (max. 16 channels). 1 s s s n n n n 0 x x x x x x x 0 y y y y y y y Status Data 1 Data 2 1 byte
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MIDI Messages There are two main types of MIDI messages: channel and system As their names indicate they are addressed to individual channels or the whole system (exception: “omni on” channel messages)
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Channel messages Message Status Data 1 Data 2 Note off 8n Note number Velocity Note on 9n Note number Velocity Polyphonic aftertouch An Note number Pressure Control change Bn Controller number Data Program change Cn Program number - Channel aftertouch Dn Pressure - Pitch wheel En LSbyte MSbyte MIDI channel numbers (n) are referred as 1 to 16, while in reality they are represented by binary values 0 to 15 (0-F). Example: the status byte of a note off message for channel 7 is “86”
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Note on / Note off (1) They make the bulk of the information commonly sent through a MIDI channel “Note on” triggers a musical note, “note off” turns it off All notes MUST be turned off (otherwise they’ll sound indefinitely) Message Status Data 1 Data 2 Note off 8n Note number Velocity Note on 9n Note number Velocity
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Note on / Note off (2) There are 128 (0-127) possible note values (~10 octaves) mapped to the chromatic western music scale. Commonly, middle C is mapped to MIDI’s C-3 (note number 60, 6th octave).
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Note on / Note off (3) Note on messages are also associated to a “velocity” value, characterizing how hard the key was hit. Note on velocity can be used to control volume and timbre of a sound (e.g. by controlling the scaling of an envelope generator) The mapping between velocity and the parameter it controls is often logarithmic. Note off velocity relates to the speed at which a note was released It could be used to affect a sound, but it is not normally used.
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Note on / Note off (4) Note on, velocity zero is equivalent to note off. It is convenient when large amounts of data are sent to the MIDI bus (e.g. a high-polyphony chord) Normally we will need 6 bytes for each note of a chord: [9n] [pitch][velocity] and [8n][pitch][velocity] Instead we can clutter note on and off messages together: [9n] [pitch][vel][pitch][vel]…[pitch][vel] This is known as running status For a 4-note chord it means 17 bytes are transmitted rather than 24 bytes (assuming running status remains unchanged).
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Aftertouch Key pressure messages are called aftertouch It refers to the amount of pressure placed on a key at the bottom of its travel (triggering performance parameters, e.g. vibrato)
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9_MIDI_code - MIDI Code Juan P Bello MIDI Code: the message...

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