[LAU] MIDI over USB

Will Godfrey willgodfrey at musically.me.uk
Sat Jun 2 00:32:17 CEST 2018


On Sat, 2 Jun 2018 00:12:58 +0200
Robin Gareus <robin at gareus.org> wrote:

>On 06/01/2018 11:45 PM, Will Godfrey wrote:
>> On Fri, 1 Jun 2018 22:50:50 +0200
>> Robin Gareus <robin at gareus.org> wrote:
>>   
>>> On 06/01/2018 09:00 PM, Will Godfrey wrote:  
>>>> Something just occurred to me.
>>>>
>>>> Does anyone know if this is transmitted any faster if going computer to computer
>>>> rather than between hardware devices. So do you get lower latency?    
>>>
>>> You have more bandwidth but not usually lower latency.
>>>  
>>>> Also what about keyboards that work entirely as MIDI over USB connecting to a
>>>> computer?    
>>>
>>> Depends on the keyboard.
>>>
>>> It seems that may chipsets still use the 31.25kbaud (probably because
>>> you can get USB to physical MIDI ASIC cheap off the shelf).
>>>
>>> You can check with jack_midi_dump (or similar). Elbow press/release
>>> 30-40 notes on a keyboard and check if most individual note events are
>>> spaced less than 1ms apart. If they are, then the interface is faster
>>> than physical MIDI.
>>>
>>> ciao,
>>> robin  
>> 
>> Now why didn't I think of that?
>> Thanks Robin :)
>>   
>
>I just tested with a M-Audio Oxygen 49 (which only has USB MIDI)
>
>I've used an A4-book to press/release 14 white keys, recorded it with
>Ardour. The 14 note-off events span 220 samples (@48kHz, ~4.5ms).
>
>So the device has a higher bandwidth than physical MIDI (approx 3
>times). I can't say anything about the latency though.
>
>All other devices that I have here do have an physical MIDI port (5pin
>DIN) and are only 31.25 kbaud have ~2.0ms round-trip latency.
>
>Cheers!
>robin
>
>PS. note-on events are spread out further because I didn't manage to
>press the book (or elbow) down accurately enough.

That is actually very interesting, and useful.

With hardware MIDI a two-handed 4 note chord (so 8 total) has a 'ripple' of at
at the very least 8mS. Although a musician is likely to be more varied than
that, something like a drum machine wont, and this effect can be very noticable.
it would suggest that where you have a keyboard with both options you should
use USB for preference.

I have a Miditech pro49 that has that combination, so must check to see if
that's true, or if the two outputs are locked together.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.


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