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Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Hi all,
I'm asking some help from someone who already built a MIDI Interrupter with Pitch Bend...
I studied many documents about MIDI Signals, and I saw that Pitch Bend Range is defined by the controller.
I'm trying to do that with my FPGA MIDI Interrupter, but I really dont know what I should do.
Some audio experts said that normally the Pitch Bend goes from 2 semitones down to 2 semitones up (most default settings), but the problem isnt that.
The Pitch Bend is two 7 bits (LSB and MSB) data, so it gives me 16384 with 8192 as a "zero".
The Fruit Loops sends me sometimes the Minimum (from the pitch wheel) of 6827 and max of 9557, and other times it sends 7510 as minimum and 8874 as max. It can even be different than that.
I didnt find where it defines from where to where the pitch goes, or if its a fixed note range with the Whell.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
The pitch bend is two bytes, for a total rangin 0 to 16384. If the value is less than 8192, it is a pitch down. If it is greater than 8192, it is a pitch up. I imagine there is a standard of how far it bends, but it's not encoded in the midi stream as far as I know, since there is a variable in my code of pitch_wheel_steps. Here is the code for pitching from my ATMEL controller:
if(pval<8192){ //pitch down command int freqLOW = noteFreqs[note-pitch_wheel_steps]; return map(pval, 0, 8192, freqLOW, initfreq); //returns a mapped result } else{ //pitch up command int freqHIGH = noteFreqs[note+pitch_wheel_steps]; return map(pval, 8192, 16383, initfreq, freqHIGH); //returns a mapped result }
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
MRacerxdl wrote ...
I saw that GM recommends to bend from two semitones lower to two semitones higher (or one tone up and down).
the noteFreqs array is only the octaves note, or you made a table with steps between the semitones?
I will post more details of my interrupter soon. I need to write a documentation.
As I made on a FPGA, it may help much people to design their own MIDI Interrupters :D
An overview:
Thanks for the help!
NoteFreqs is an array with the frequency of each midi note. So for wheel<8192 it grabs the frequency of the target note minus pitch-wheel-steps, which is what the frequency would be if the pitch wheel signal were zero. It then maps the pitch wheel between 0 and 8192 to the fully pitch wheeled note through normal note. The equivalent occurs for if the pitch wheel is greater than 8192, except it is adding rather than subtracting. There is no need for an array of tones between semitones.
I would be curious to see your FPGA work, but the link you posted is dead.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
lol, i didnt get it what you done lol [EDIT] I didnt understand what that map function does... I never used that lol
Here is another link to the pic: (Big Pic)
It is basicly what all people do with uC. I made state machine to process the three bytes of midi. If I turn on a note, the state machine will search for an available PWM to set the period. Also it calcs in realtime the tOn of the note, with it will be 5% of period on max of 180us (can be set)... Also I have a protection on the output that sets the maximum tOn to 250us (in case I have some bug at the code)
I will post the source code soon too :D
The sound is pretty good now:
The video isnt good, because I noticed only after doing this video that my Cellphone has two mics and now only one (and I only put a tape on one)...
But it was much bugs in my design when I done that video, now I corrected all. Hope to test it soon.
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MIDI Pitch Bend Help
