MIDI tuning standard

MIDI Tuning Standard (MTS) is a specification of precise musical pitch agreed to by the MIDI Manufacturers Association in the MIDI protocol. MTS allows for both a bulk tuning dump message, giving a tuning for each of 128 notes, and a tuning message for individual notes as they are played.

Frequency values

If Template:Mvar is a frequency in hertz, then the corresponding MIDI note number Template:MvarTemplate:Sub is given by the formula

$N_{𝖬𝖨𝖣𝖨}=69+12\cdot {\log }_2\left(\frac{f}{440\mathrm{H}\mathrm{z}}\right)=69+\frac{12}{\log 2}\log \left(\frac{f}{440\mathrm{H}\mathrm{z}}\right),$

where "Template:Math" in the second expression is any logarithm (e.g. either the common logarithm Template:Math , the natural logarithm Template:Nobr , or any other).

The quantity Template:Nobr is the number of octaves above the 440 Hz concert A, or A₄, or [[Helmholtz pitch notation|Template:Math′]] . Multiplying it by 12 gives the number of semitones above 440 Hz (the value is negative if the frequency Template:Mvar is lower in pitch than 440 Hz). Adding 69 (decimal, or 0x45 hexadecimal) gives the number of semitones above the C five octaves below middle C.

Not only is 440 Hz the standard central pitch for MIDI, it is also widely used as the concert A standard pitch (ATemplate:Sub e.g. USA, UK), and since that is represented in MIDI signals by the integer 69 (nine semitones above middle C (CTemplate:Sub, Template:Math), which is 60 decimal or 0x3C hexadecimal), this gives a real number which expresses pitch in a manner consistent with midi and integer notation, known as the MIDI note number, Template:Nobr

Converting from MIDI note number (Template:MvarTemplate:Sub) to frequency (Template:Mvar) is given by the following formula:

$f=440𝖧𝗓\cdot 2^{[(N_{𝖬𝖨𝖣𝖨}-69)/12]}=440𝖧𝗓\cdot \exp \left[\frac{\ln 2}{12}(N_{𝖬𝖨𝖣𝖨}-69)\right].$

Frequency Data Format

The frequency data format allows for the precise notation of frequencies that differ from equal temperament.

"Frequency data shall be defined in [units] which are fractions of a semitone. The frequency range starts at MIDI note 0, C = 8.1758 Hz, and extends above MIDI note 127, G = 12543.854 Hz. The first byte of the frequency data word specifies the highest equal-tempered semitone not exceeding the frequency. The next two bytes (14 bits) specify the fraction of 100 cents above the semitone at which the frequency lies. Effective resolution = Template:Nowrap = .0061 cents."

This higher resolution allows a logarithmic representation of pitch in which the semitone is divided into Template:Nowrap, which means the octave is divided into Template:Val (logarithmically) equal parts. These parts are exactly Template:Sfrac cents (approximately 0.0061 cents) in size, which is far below the threshold of human pitch perception and which therefore allows a very accurate representation of pitch.

Applications

The precision pitch values may be used in microtonal music, just intonation, meantone temperament, or other alternative tunings.

Software which supports MTS includes Scala, TiMidity++, ZynAddSubFX and FluidSynth.

Software plugin instruments which support MTS include Native Instruments FM8, Synthogy Ivory, and Xen-Arts' various xenharmonic VSTi plugins, including the FMTS FM synthesizer, Ivor virtual analog synthesizer, and XenFont SoundFont sample player.

Hardware instruments in current production which support MTS include: Dave Smith Instruments (DSI) Rev-2, Prophet-12, Prophet-6, Oberheim OB-6, Moog Sub37, Minitaur, Novation Bass Station II, Peak, Sonoclast Plastic Pitch MIDI Microtuner, and the Waldorf Kyra.

See also

• Microtonal music
• Microtuner
• Musical tuning

External links

• MTS specification