[sdiy] USAMO

[Neil Johnson]

> That page says
>
>   "Because the MIDI signals are generated and transported as audio,
>   they are guaranteed to be sample-accurately synced with your audio,
>   and free of the jitter often associated with computer-generated
>   MIDI."
>
> this seems to be an inaccurate claim. It would be possible to do this,
> but the same box would need to either have several channels of audio
> in and out (plus preamps, etc) to be sample-accurate *with*, or
> alternatively some digital in-out, for example ADAT, plus a wordclock
> source so that some other box could be kept aligned to a granularity
> of one sample.
>
> As a standalone box, its not sample-accurate with anything else.

I think the point here is that, by being sample-accurate to itself
(which is all it can be) it removes the OS timing jitter that would
otherwise get with a direct MIDI out.  I suspect the "trim" control is
a time offset that allows you to adjust the relationship between the
audio and the MIDI tracks.

You will certainly get a delay between a MIDI event in the DAW and the
start of the MIDI bytes coming out of the box, but as long as that
delay is the same and fixed the result should sound much tighter.  In
the DAW you might be able to fix this by introducing a small delay in
the audio-only path to compensate for this, and ideally once
calibrated it should never need modifying.

Not to mention the fact that a single MIDI event in a DAW may be
time-accurate to within +/-21us (@48kHz), but considering most common
MIDI messages are 3 bytes long it will take ~960us before the
receiving MIDI instrument has enough information to do something.

Neil
--
http://www.njohnson.co.uk