Re: Questions on data in MIDIPackets
Re: Questions on data in MIDIPackets
- Subject: Re: Questions on data in MIDIPackets
- From: Brian Willoughby <email@hidden>
- Date: Sun, 24 Feb 2002 20:50:14 -0800
[ on 2/21/02 4:42 PM, Brian Willoughby <email@hidden> wrote:
[ > longer bits streams such as USB will probably always receive
[ > entire packets with a single time stamp.
[
[ Lacking knowledge of details here, it sounds like multiple MIDI
[ messages get packaged with a single time stamp. This sounds
[ unfortunate, unless this clumping could be done intelligently
[ (e.g. only if the message time difference is less than the desired
[ threshold of accuracy). Certainly time-stamp per MIDI message
[ from source to destination would be the ultimate. No doubt future
[ interfaces will go in that direction unless it turns out not to
[ matter.
I think we've confused the issue by using terms which may not exactly be
standard. Herbie and I (with others) have been discussing MIDI 1.0 vs.
USB-MIDI. MIDI 1.0 is a stream of discretely transmitted bytes where 1, 2, or
3 bytes make up a MIDI message (except SysEx). USB-MIDI transfers 32-bit
words, so the entire MIDI message is always contained in the data received
(again, excepting SysEx).
The discussion had been centered around whether the time stamp of the first
byte or last byte (or even before the first byte) would be used for MIDI 1.0,
but USB-MIDI doesn't need to consider this question since all "bytes" arrive
together. By "longer bits stream such as USB" I was referring to the 32-bit
USB transfer words, and I don't really know why I used the term "entire
packets" when I could have simply called them "complete MIDI messages."
I hope this clears things up for you, and allays any fears you may have had
about the potential for CoreMIDI foolishly stamping multiple MIDI messages with
the same time stamp (it doesn't, so far as I know, unless a USB-MIDI device
were to set the same time stamp for multiple message through some other means).
Brian Willoughby
Sound Consulting
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