Re: USB MIDI to OSX - throughput, etc.
Re: USB MIDI to OSX - throughput, etc.
- Subject: Re: USB MIDI to OSX - throughput, etc.
- From: Herbie Robinson <email@hidden>
- Date: Mon, 8 Aug 2005 22:38:42 -0400
At 11:51 AM -0700 8/8/05, Chris Graham wrote:
What's the throughput of USB MIDI to OSX? I assume it's not limited to the
31250 bps of MIDI, but I can't find a specification for this.
It would depend on how the adapter was implemented.
Also, I understand that OSX now has a low latency, low jitter, built in USB
MIDI driver.
Apple provides an API that can support multiple MIDI drives. The
also provide some drivers for standard hardware (USB and maybe
Firewire). The API includes time stamping if the drive can support
it. Time stamping, in theory, could provide extremely low jitter
output and capture. Time stamping does not help latency (with the
definition of latency that applies to recording music). The last
time I looked, there wasn't anything in the API to off-load echoing
of MIDI input to the driver or hardware level (which would help
latency).
I've measured round trips in the 2-3 msec range with jitter of about
2 msecs (on inexpensive interfaces). It's a little better with high
end interfaces that use time stamps, but not much. This leads me to
suspect that the OS is actually performing better than the adapters
(the CPUs in those adapters are not exactly speed demons...).
Does this work with USB midi according to the USB Developers
Assoc spec, or is it an enhanced protocol, say with time stamps?
I believe Apple provides an official USB class driver, but the USB
standard doesn't provide for time stamps; so, if there is no
proprietary driver for a given USB interface, there are no time
stamps. I can tell you that MOTUs drivers for the 8 port interfaces
support time stamping but they do not support it for the Fastlane.
The last time I checked, Midiman's 2 port interface didn't, but it
has downloadable firmware; so, maybe it does, now.
--
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