11 Sep
2004
11 Sep
'04
1:17 a.m.
On Friday 10 September 2004 05:50 pm, Martijn Sipkema wrote:
[...]
FWIW the M-Audio keyboard I bought has a regular MIDI interface too. I'd
imagine one with audio inputs has it as well.
The problem here is that class compliant devices
suffer bad timing
because they use bulk transfers for MIDI data. The standard for
MIDI over FireWire is much better.
I don't agree on the subject that USB bulk transfers cause bad MIDI
timing. Of course, you can't use the same USB host controller at a time
with a MIDI interface and some other device like a CD writer and expect
both good MIDI timing and fast CD burning. If you can reserve a host
controller exclusively for your USB MIDI device, you will get pretty good
results, most of the time. - Isochronous transfers send or receive data
streams in realtime with
guaranteed bus bandwidth but without any reliability.
[...]
MIDI streams need to be reliable (a single byte
lost isn't acceptable),
so Isochronous is not an option. Interrupt or Bulk transfers are very
similar: they use only the available bandwidth at each moment, so there
can be unwanted delays and timing problems. Some manufacturers'
proprietary protocols include a timestamp with each USB MIDI packet to
enhance the time accuracy, but this can be done either in bulk or
interrupt transfers.
MIDI streams need a reliable transport with guaranteed bandwidth. If
USB can't provide this, then it is not really suitable for MIDI, but I'm
not saying it is unusable, just that it may perform worse then traditional
serial multiport MIDI interfaces.
--ms