Tuning RPNs: Difference between revisions

<h2>IMPORTED REVISION FROM WIKISPACES</h2>

This is an imported revision from Wikispaces. The revision metadata is included below for reference:<br>

: The revision comment was: <tt></tt><br>

The revision contents are below, presented both in the original Wikispaces Wikitext format, and in HTML exactly as Wikispaces rendered it.<br>

There are 3 parts to a tuning message: the input note, the output note, and the pitch bend. The input note is a midi note number which specifies a physical **__key__** on the controller. The output note is a midi note number which specifies a __**pitch**__ in the standard A-440 12-ET tuning. The pitch bend, which is the exact same format as the 2 data bytes of a standard midi pitch bend message, specifies how much to bend the output pitch. Upon receiving the input note, the synth produces this frequency:

The pitch bend range is "hard-wired" to 2 semitones, one sixth of an octave, hence the 6 at the end of the equation. If the physical pitch bend wheel is moved, that bend would be added onto the tuning bend. The physical pitch bend wheel is not hard-wired to 200¢ and is governed by the usual pitch bend range.

Because microtonalists use array keyboards, there may be a full 128 keys in use. Any input key can be mapped to any output frequency. Because alternate tunings can have more than 12 notes per octave, more than one input note may be be mapped to the same output note. Therefore the pitch bend is associated with the input note, not the output note. Specifying an output note is optional. If none is specified, the output note is understood to be the same as the input note.

This might be easier to understand if a hardware implementation is visualized. Imagine a 10-and-a-half octave keyboard with 128 keys. Behind each key is a tiny transposing slider and a tiny pitch bend wheel. The slider runs from 0 to 127 and sets that key's output pitch. The slider doesn't travel smoothly, rather it clicks into place on the whole numbers. The pitch bend wheel runs from -200¢ to 200¢ and sets the bend. When the keyboard is first turned on, all these wheels are set to center and all the sliders are set to match the key -- the lowest key's slider is 0, the 2nd one is 1, etc. Unlike the usual pitch bend wheel, which this keyboard also has, the tiny wheels don't have a spring that returns them to center. If one is moved to +30¢, it stays there until moved again. Using the sliders and wheels, any key on the keyboard can be set to play any pitch in the entire 10-and-a-half octave midi range. The synth's job is to produce whatever pitches are required by the keys and sliders and wheels, which may be further bent by the usual pitch bend wheel.

Sometimes the keyboard will actually be a touchscreen device, and instead of pressing a key, the musician simply touches the screen to play a note, with the touch's location determining the pitch. Dragging one's fingers along the surface generates ultra-wide pitch bends. This is a polyphonic device, with each finger being in effect a separate "key". There may be no retuning software, because the controller (or iPad app) will generate its own tuning messages. The imaginary keyboard analogous to this device has no tiny wheels and each tiny slider can travel freely without clicks. From the synth's point of view, the midi stream is the same as from a standard controller: note-ons and note-offs mixed with tuning messages and perhaps standard pitch bends.

**__Implementation__:**

//(We've recently discovered that RPN data messages are not completely supported, and are considering alternatives to RPNs like undefined CCs, user-defined CCs, and keyswitches - Ed.)//

There are 3 parts to a tuning message: the input note, the output note, and the pitch bend. The input note is a midi note number which specifies a physical &lt;strong&gt;&lt;u&gt;key&lt;/u&gt;&lt;/strong&gt; on the controller. The output note is a midi note number which specifies a &lt;u&gt;&lt;strong&gt;pitch&lt;/strong&gt;&lt;/u&gt; in the standard A-440 12-ET tuning. The pitch bend, which is the exact same format as the 2 data bytes of a standard midi pitch bend message, specifies how much to bend the output pitch. Upon receiving the input note, the synth produces this frequency:&lt;br /&gt;

&lt;br /&gt;

&lt;br /&gt;

The pitch bend range is &amp;quot;hard-wired&amp;quot; to 2 semitones, one sixth of an octave, hence the 6 at the end of the equation. If the physical pitch bend wheel is moved, that bend would be added onto the tuning bend. The physical pitch bend wheel is not hard-wired to 200¢ and is governed by the usual pitch bend range.&lt;br /&gt;

&lt;br /&gt;

Because microtonalists use array keyboards, there may be a full 128 keys in use. Any input key can be mapped to any output frequency. Because alternate tunings can have more than 12 notes per octave, more than one input note may be be mapped to the same output note. Therefore the pitch bend is associated with the input note, not the output note. Specifying an output note is optional. If none is specified, the output note is understood to be the same as the input note.&lt;br /&gt;

&lt;br /&gt;

This might be easier to understand if a hardware implementation is visualized. Imagine a 10-and-a-half octave keyboard with 128 keys. Behind each key is a tiny transposing slider and a tiny pitch bend wheel. The slider runs from 0 to 127 and sets that key's output pitch. The slider doesn't travel smoothly, rather it clicks into place on the whole numbers. The pitch bend wheel runs from -200¢ to 200¢ and sets the bend. When the keyboard is first turned on, all these wheels are set to center and all the sliders are set to match the key -- the lowest key's slider is 0, the 2nd one is 1, etc. Unlike the usual pitch bend wheel, which this keyboard also has, the tiny wheels don't have a spring that returns them to center. If one is moved to +30¢, it stays there until moved again. Using the sliders and wheels, any key on the keyboard can be set to play any pitch in the entire 10-and-a-half octave midi range. The synth's job is to produce whatever pitches are required by the keys and sliders and wheels, which may be further bent by the usual pitch bend wheel.&lt;br /&gt;

Sometimes the keyboard will actually be a touchscreen device, and instead of pressing a key, the musician simply touches the screen to play a note, with the touch's location determining the pitch. Dragging one's fingers along the surface generates ultra-wide pitch bends. This is a polyphonic device, with each finger being in effect a separate &amp;quot;key&amp;quot;. There may be no retuning software, because the controller (or iPad app) will generate its own tuning messages. The imaginary keyboard analogous to this device has no tiny wheels and each tiny slider can travel freely without clicks. From the synth's point of view, the midi stream is the same as from a standard controller: note-ons and note-offs mixed with tuning messages and perhaps standard pitch bends.&lt;br /&gt;

&lt;br /&gt;

&lt;br /&gt;

&lt;strong&gt;&lt;u&gt;Implementation&lt;/u&gt;:&lt;/strong&gt;&lt;br /&gt;

&lt;br /&gt;

&lt;em&gt;(We've recently discovered that RPN data messages are not completely supported, and are considering alternatives to RPNs like undefined CCs, user-defined CCs, and keyswitches - Ed.)&lt;/em&gt;&lt;br /&gt;