[sdiy] Hi From Terry

Brian Willoughby brianw at audiobanshee.com
Mon Mar 14 01:11:50 CET 2016


Hi Terry,

You don't say anything about sound generation features except for 8 or 16 channel polyphonic. From that, I assume that you're interested in a non-sound-generating MIDI keyboard that only outputs MIDI messages, not sounds or CV.

If that is the case, then polyphony really isn't a matter of the keyboard itself, but is actually a limitation (or not) of the connected sound module. A MIDI keyboard should simply send out Note On and Note Off messages without any consideration for polyphony. Even the Arpeggiator would be generating one note at a time, so polyphony isn't an issue there.

The sequencer feature might start to bring in considerations of polyphony, but then it's more of an aesthetic. There's something to be said for the limitations of a monophonic sequencer, where additional tracks/channels are needed to control multiple notes at the same time. On the other hand, if you're willing to complicate your software and your user interface, then a single sequence could hold chords as well as notes, but then editing becomes slightly more complex.

As for processor choice, I think that the M3 should be sufficient for MIDI, even a Cortex M0. I'm working on a new design with the TM4C1294, which is a Cortex M4, but I only chose it because I need floating point support. I see no reason why a MIDI master keyboard would need floating point, so you can look for cheaper ARM chips. I think that the newer M0 models are designed to compete with older 8-bit chips. All you really need is one UART peripheral for each MIDI I/O pair. The TM4C1294 has 8 UART peripherals, so I plan on supporting up to 8 MIDI Inputs and 8 MIDI Outputs.

In your case, what would MIDI In do?

Personally, I'm a big fan of separating the MIDI master keyboard from the sound generation. That frees up the options to tailor the physical keyboard to the player, while also allowing maximum flexibility for sounds, regardless of playing style. It's the whole raison d'être for MIDI in the first place.

Brian Willoughby


On Mar 13, 2016, at 4:37 PM, thx1138 at earthlink.net wrote:
> Hi Neil,
> 
> Well I am swamped with work and have not had a chance to put much mail out to friends for a while.
> 
> I did have a question, who builds the best Midi Keyboard DIY project out there these days?
> 
> My E-Mu 4065 keyboard is non midi and will never be, but I wanted to look at cortex M3 , M4 and M7 as a replacement for this platform instead of a Z-80.
> 
> Z-80, sounds old I know, but it was the beginning for me at Oberheim and E-Mu.
> 
> Time to move forward and see what projects people have done.
> 
> I need:
> 
> Midi In/Thru/Out
> 
> Polyphonic up to 16 voice ideal, but I could live with 8 channels.
> 
> Poly Sequencer
> 
> Arpeggiator
> 
> Pitch Bend 
> 
> Transpose 
> 
> etc.
> 
> I may have to build this as much of the stuff I have seen leaves me wanting a better software implementation.
> 
> Let me know what you think.
> 
> best regards,
> 
> Terry




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