Tuning RPNs: Difference between revisions

: This revision was by author [[User:TallKite|TallKite]] and made on <tt>2013-09-14 21:52:03 UTC</tt>.<br>

: The original revision id was <tt>451155272</tt>.<br>

The new method uses RPNs (Registered Parameter Numbers). The technical details: There are about 16,000 possible RPN parameters, and only about a dozen are in use. We can use a block of 128 RPNs, one for each note number, for retuning. Data MSB and LSB messages for these RPNs contain the cents to retune by, in the exact same format as the standard midi pitch bend message. The retuning is immediate (real-time), just like the standard pitch bend. This makes it easier for the synth developer or designer, because he has already written code that deals with physical pitch bend wheel movement, and can just reuse it to deal with tuning RPNs. We use either a data increment or a data decrement message to transpose the input note by so many semitones, allowing for non-12-note tunings. If the RPN MSB is 100 = 64 hexadecimal, then to bend note nn on channel c to note mm with bend of yyzz would take up to 5 midi CC (Controller Change) messages. In hexadecimal the midi looks like this:

RPN LSB: Bc 64 nn (note to retune, 64 means set RPN parameter LSB)

A possible conflict arises with NRPNs, which use the same data inc/dec/MSB/LSB messages. The solution is for the tuning software to monitor the midi stream for NRPNs, and if found, take these steps: Remember the current NRPN parameter number, not omit the RPN MSB and LSB when retuning, and send a NRPN MSB/LSB message after retuning to restore the current NRPN parameter. Similar steps should be taken if one of the few RPNs already defined are encountered.

One aim of the tuning RPN method is to make extremely wide pitch glides possible. The synth should be able to retune a note as it's being played. Specifically, a data inc/dec message that changes the output note number should not trigger a new ASDR envelope. That should only happen in response to note-ons. The midi stream for pitch glides will be reduced to mostly data LSBs, with data MSBs whenever the MSB boundary is crossed, and data inc/dec whenever the note boundary is crossed.

The new method uses RPNs (Registered Parameter Numbers). The technical details: There are about 16,000 possible RPN parameters, and only about a dozen are in use. We can use a block of 128 RPNs, one for each note number, for retuning. Data MSB and LSB messages for these RPNs contain the cents to retune by, in the exact same format as the standard midi pitch bend message. The retuning is immediate (real-time), just like the standard pitch bend. This makes it easier for the synth developer or designer, because he has already written code that deals with physical pitch bend wheel movement, and can just reuse it to deal with tuning RPNs. We use either a data increment or a data decrement message to transpose the input note by so many semitones, allowing for non-12-note tunings. If the RPN MSB is 100 = 64 hexadecimal, then to bend note nn on channel c to note mm with bend of yyzz would take up to 5 midi CC (Controller Change) messages. In hexadecimal the midi looks like this:&lt;br /&gt;

RPN LSB: Bc 64 nn (note to retune, 64 means set RPN parameter LSB)&lt;br /&gt;

A possible conflict arises with NRPNs, which use the same data inc/dec/MSB/LSB messages. The solution is for the tuning software to monitor the midi stream for NRPNs, and if found, take these steps: Remember the current NRPN parameter number, not omit the RPN MSB and LSB when retuning, and send a NRPN MSB/LSB message after retuning to restore the current NRPN parameter. Similar steps should be taken if one of the few RPNs already defined are encountered.&lt;br /&gt;

One aim of the tuning RPN method is to make extremely wide pitch glides possible. The synth should be able to retune a note as it's being played. Specifically, a data inc/dec message that changes the output note number should not trigger a new ASDR envelope. That should only happen in response to note-ons. The midi stream for pitch glides will be reduced to mostly data LSBs, with data MSBs whenever the MSB boundary is crossed, and data inc/dec whenever the note boundary is crossed.&lt;br /&gt;