10_MIDI_soundcontrol

10_MIDI_soundcontrol - MIDI sound control Juan P Bello...

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MIDI: sound control Juan P Bello
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Interpreting MIDI MIDI code is the language used to communicate between devices Still, each device might decide to interpret the code in its own way according to its capabilities and functionalities The MIDI implementation for a particular sound generator should be described by a so-called MIDI implementation chart which is commonly part of its manual It indicates which messages are received and transmitted, as well as limitations and uncommon features For example a device might be able to receive all possible note numbers (0-127) but only able to transmit a sub-set of those (e.g. 16-115)
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Polyphony and voices Most current sound generators (e.g. synthesizers and samplers) are polyphonic (with a cap on the maximum number of notes) When the polyphony of a device is exceeded, a predefined strategy is activated that governs how to handle the extra notes Different strategies include: releasing the “oldest” or “quietest” notes first, or simply not accepting any new notes until current notes are released The degree of polyphony of a device is different from the number of voices it can generate How the polyphony is distributed amongst the voices is, again, device specific Allocating polyphony according to demand is perhaps the most common approach nowadays Current systems are capable of generating several voices at the same time, independent of polyphony considerations
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Velocity and aftertouch Note velocity and aftertouch can be used to control specific functions within the sound generation chain Note off velocity, uncommon in many devices, can be used to control the release time of the note, reverberation time, etc Filter Oscillator Envelope After touch Pitch Velocity brightness Gain Sound LFO vibrato
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General MIDI (1) Although program change can be used to select voice patches, there is no guarantee that the same voice will be recalled by the same message in different instruments E.g. program change message 10 may refer to “trombone” on one instrument and “ukulele” on another. This makes the exchange of songs between instruments very difficult, as their reply will be different on every device. General MIDI is an attempt to standardize the behavior of sound generators in the presence of MIDI files. Three types: General MIDI Level 1 (GM1), GM Lite (GML) and GM Level 2 (GM2)
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General MIDI (2) GM 1 specifies a standard voice map: Precise voice names can be found in the GM documentation Program (decimal) Sound Program (decimal) Sound 0-7 Piano 64-71 Reed 8-15 Chromatic Percussion 72-79 Pipe
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10_MIDI_soundcontrol - MIDI sound control Juan P Bello...

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