Dan Wilson misquoted my comment about Duo-Art expression levels by
pasting two sentences together which didn't make sense.  If we "quote"
each other, I feel it is required to not take things so completely out of
context as to make the other sound foolish!

I would also like to explain that had I wanted to go into detail about
Duo-Art coding, I could have said that while Duo-Arts are set up to
"trigger" the Theme response waiting on the expression box, it IS
possible to "lead" the system and catch a few expressions on the fly.
However, that is NOT the basic design of the Duo-Art.  That is a _coding
technique_ to work around the limitations of the system.  Please
acknowledge the difference.  Dan stated:

> I've never seen any theorizing about the Duo-Art that takes proper
> account of the exponential delays that in fact take place in the
> suction level changes, and are significant once the level change is
> more than say 5 or 6.  It takes something like a third of a second
> for a fresh level to be established, against Ampico's 0.1 second.
> So all the fast coding in Duo-Art rolls has to compensate for this
> by dotting in higher or lower levels than are strictly needed, just
> to get a steeper slope.

Beginning at square one: Time is always linear.  There is no such term
as an "exponential delay," so I don't know what that means.  Suction
level changes with regard to expression steps in a Duo-Art are always
linear, not exponential.  (Loudness is exponential when measured against
pressure, but that isn't addressed.)

The claim that we can bank on a third of a second per change in a Duo-Art
is unclear, since the accordions during quickly changing passages of the
music are always in rapid motion, changing the spring tension constantly.
Since it's the spring tension primarily which determines how quickly the
expressions can set up (assuming valve travel is optimized) the real
answer is, "There is no specific fraction of a second which one can trust
to be the timing unless you first specify which expression box you are
speaking about, and which section of the accordion!"  Spring tension
increases as more sections get pulled down.  A shorter section takes half
as much time as the section below it, etc. etc.

I also would like to correct the notion that an Ampico is able to react
to a new expression level in a tenth of a second.  That is grossly
understated and can be proven a number of different ways.  However, my
article in the MBSI a few years ago entitled, "The Capabilities of the
Ampico" should definitely put this misconception to rest!  You can see
that this is not right when all you have to do is measure on the roll
just how close an expression code can be to the note accented.

To figure the necessary lead time of an expression, it's really simple.
You just divide the measured expression lead (the shortest you can find,
of course) by the number of inches per second the roll is traveling.  For
example, at a tempo of 80, it is going 1.6"/sec we'll say.  That means it
takes a lead time of about .03 sec to resolve a .050 inch lead.  You'll
find that very comfortable tolerance all over the place.  If the shortest
resolution of an Ampico was, as Dan says, .1 second, then the closest
expression hole to an accented note at tempo 80 would be roughly 3/16"!
That would not allow an Ampico to be called a reproducer!

Also, in defense of the Ampico valves in a Duo-Art Vorsetzer, I find no
real proof that an Ampico valve just couldn't cut the mustard.  If the
purpose of the letter was to show that these valves are inferior to
Duo-Art valves or to imply that the instrument didn't perform well
because of the valve used, then I have to object to that.  There is
really nothing all that spectacular in the performance of either the
Aeolian or Ampico valve.  Either one is perfectly adequate for the task.

If you want to get into some really spectacular valves, we can do that!
For example, one of the finest in all playerdom was the late model
Straube hinged swing valve!  Another was the (properly rebuilt) Schultz
valve.  There were plenty of valves on the market that could play rings
around Aeolian and Ampico.  The fact is, however, the overkill wasn't
required, and manufacturing costs were more important!  Probably the very
best valve of all time (overall) was the Ampico model B valve.  But had
it been built under the Straube patent with a ball bleed, it would have
definitely set the all-time record for speed and sensitivity.

Craig Brougher