Dave Saul suggested, in 031003 MMDigest, "Suppose a pressure sensor
were interposed between key and balance rail ..."

I suggest a carbon pile resistance-pressure transducer placed
between the balance rail and the keyframe.  This ancient device,
I understand, is still used in the foot pedal that controls the
motor speed of the ubiquitous Singer electric sewing machine.
It is sensitive and rugged and very capable of modulating battery
current passing through the low-impedance inking magnet.

The carbon pile pressure transducer is a stack of carbon wafers that
resembles a short pile of coal-black coins or poker chips (gaming
tokens).  The electrical conductance varies in approximate
proportion to the force that squeezes together the conductive wafers.
It is related to the carbon-button telephone transmitter that
squeezes carbon granules to modulate the current.

The resulting recording of the summed key forces upon the balance rail,
although not an accurate representation of hammer or key velocity,
would nonetheless provide useful data to guide the work of the music
roll editor; it might possibly be as useful as the 'seismograph'
recordings made many years later by DeLuxe for Welte Licensee rolls.

The Welte music roll editors of 1904 (or any era) were certainly
capable of creating reproducing piano rolls without benefit of recorded
hammer or key velocity data -- witness the thousands of Duo-Art and
Ampico and Apollo rolls sold.  But the roll performances improved when
the editors were provided dynamics data, as can be heard in Ampico and
Welte Licensee music rolls produced without and with the benefit of
a dynamics recording.

I think all music roll editors would agree that any sort of force or
velocity data is better than no data.  The consistently good dynamics
coding of the Welte-Mignon music rolls strongly suggests that some sort
of dynamics recorder, whether it was exotic or simple, was employed at
their recording studios in Freiburg and Poughkeepsie.  We simply have
no trustworthy detailed account of the _actual system_ employed to
create the Welte-Mignon T-100 "Red" music roll performances.

An illustration of a recording by the DeLuxe 'seismograph' pen recorder
is at  http://mmd.foxtail.com/Pictures/Welte/seismic.html

Robbie Rhodes