Elektron Musical Instruments

i thought i'd put claims about the stability of the
machinedrum's clock stability to the test.  jump down to the
"findings" section if the details bore you.

environment:

1. MD connected directly to a motu micro lite USB, with no
other devices attached.

2. the micro lite is connected to a mac g4 running os X
panther on a sonnet PCI card.  the keyboard and mouse are on
the motherboard's bus.

3. the mac runs snoize's "MIDI monitor" application.

known issues:

1. MIDI over USB is purportedly not jitter-free.  there is no
published spec for the MIDI interface's jitter that i know
of, so it's something of an unknown quantity here

2. the clock in MIDI monitor may not be consistent, either,
but i hope it is.  at any rate, it times to the millisecond.

actions:

1. fire up MIDI monitor to listen for clock messages from
the MD's port

2. enable clock output on the MD

3. go and pour myself a beer.  samuel adams' imperial
pilsner is surprisingly great, if you like really hoppy
beers.

4. come back in about five minutes, stop the MD clock, and
export the data to a text file.

5. write a shell script that will output the difference
of a timestamp and the timestamp immediately preceding it
{starting with a value of zero to account for line #1} and
cat that to another file.

6. ask herself to make a pretty graph with the numbers in
the new file {i don't have excel}.

findings:

in a sample of 1001 ticks, we see 

797 ticks with 21ms between them
191 ticks with 22ms between them
13 ticks with 20 ms between them

a graph illustrating this can be seen here:

http://syncretism.net/img/drumclock.png

what does this tell us?

i'm not a statistics guy, and don't want to put any thought
into measuring jitter {deviation}, here.  this strikes me as
reasonably accurate and precise over time, and i have no way
of discerning whether the jitter is the product of the MD,
the interface, the system clock, or all three, anyway.  can
the human ear hear this?

i know that there are some tech-types among you.  was there
a better way to do this?  if so, please advise.

-- 
yours,
niall.
.. .  .   .    .     .       .           .             .                 .
aleph null.                             a simple insinuation around silence.
http://syncretism.net
.. .. gpg public key - http://www.aleph-null.net/niall.gpg .. ..