[LAU] MIDI over USB

[David Kastrup]

Will Godfrey <willgodfrey at musically.me.uk> writes:

> 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?

Computers don't generally act as USB clients but as hosts.  This is not
Firewire.  Not applicable.

> Also what about keyboards that work entirely as MIDI over USB
> connecting to a computer?

USB Low speed is 1.5Mbps and half-duplex.  Midi can be transmitted over
16 logical connectors as 32bit packets of bulk data containing a payload
of up to 3 bytes.  If you've kept up until here, you'll find that this
starts sounding fishy but then when trying to exercise all connectors,
we'd more likely be using full speed at 12Mbps (I have a Roland UM-4
Midi interface with 4 in and 4 out Midi connectors and it uses full
speed) Which is fine as long as we are not sharing the same hub with low
speed devices such as mice and keyboards and/or the hub does not have
just a single "transaction translator" for USB 1.1 compatibility in
which case Midi packets are blocked while the low-speed devices get
their data through,

So (deep breath) usually you should be fine.  There may be rare
circumstances when you aren't and they can usually be fixed by
connecting things differently.

-- 
David Kastrup