[sdiy] USB/MIDI ground isolation?

[Seb Francis]

johnspeth at yahoo.com wrote:
>> MIDI was good for 16 channels (and "appropriate" use of controllers 
>> and tempo) back then, it doesn't become unusable just because USB is 
>> faster (but, when it comes to that, being bulk-messages more jittery in 
>> timing).
>>     
>
> Yes!  I've observed what appears to be poor real time behavior of the built-in MS Windows USB/MIDI driver.  The result is the MS driver is unsuitable for dense AND/OR fast MIDI streams, IOW, any serious sequencing and performance work.
>
> Here's what I see:
>
> Note on/off messages are sent sequentially in time even though they are voiced at the same time.  For example, in a 3 note chord, the 1st note-on is sent at t=0 ms, 2nd at 2 ms, and the 3rd at t=4 ms.  Digging deeper, only one note on/off message is sent in a USB packet even though the endpoint size can accomodate many, many more messages.  It's pathetic utilization of USB capacity!  After some Google guided reading, it appears only sysex bytes are crammed into an endpoint buffer to keep it fully utilized.
>
> Does anyone know of a good realtime USB/MIDI driver that can substitute for the crappy MS driver?
>   

Presumably this is only an issue with 'class compliant' USB-MIDI 
hardware.  All of the USB to MIDI interfaces that I've come across have 
their own drivers.  Class compliant devices tend to be things like MIDI 
keyboards and other controllers which in themselves probably don't need 
very high bandwidth.

Perhaps a bigger issue with PC based sequencing is the timing of the 
software itself, which often brings overall jitter levels to many ms.  
Sadly there are very few MIDI interfaces that get around this.  
Steinberg MIDEX 3 & 8 (with LTB - Linear Time Base) is one but the 
hardware is now discontinued - still works with Cubase, Nuendo, etc.  I 
believe Emagic (now Apple) did a similar device.

Seb