Disklavier

On Mon, 13 Nov 2006, Carl Youngblood wrote:

> As I understand it, the Mark IV uses 16-bit integers for velocity as opposed
> to 8-bit integers, which I believe is what normal midi uses.  This means
> that the Mark IV can distinguish between 65,536 different velocity levels as
> opposed to 256 for normal midi.  Without changing the midi specification I
> don't see how sending a regular midi signal could take advantage of the Mark
> IV's full capabilities.


Carl, I'm afraid there may be some inaccurate statements in the above.

I've attached a document Yamaha provided through the DUG a few years ago
which explains the basics of the Disklavier Pro's XP format.  I'm not sure
whether non-Pro Mark IVs support XP playback or not.

A standard MIDI stream supports 7-bit velocity levels ("off" + 127 levels
of "on").  While it's true that MIDI involves 8-bit bytes, the highest bit
is used to distinguish command bytes from parameter values; that's why you
don't get 256 velocity levels.

XP is basically a backwards-compatible extension to MIDI that adds the
transmission of 3 additional velocity bits in a separate message preceding
the actual note message.  The note message carries the most significant 7
bits, resulting in correct playback even on MIDI equipment that doesn't
support the XP extensions.  XP-enabled equipment will watch for the
messages providing the additional 3 bits of velocity data and use it in
conjunction with the 7 bits provided through the normal note on/off
messages.  Thus, XP provides up to 10 bits of velocity levels ("off" +
1023 levels of "on").  Equipment that does not support XP will simply 
ignore the extra messages.

In the attached document, Yamaha acknowledges that while the extra 3 bits
do enhance the playback accuracy considerably, in practice, the Disklavier
can accurately reproduce only between 8 and 9 bits of resolution
(somewhere between 256 and 512 expression levels).

Achieving 65536 consistently reproducible levels in a reproducing piano is
both mechanically impossible and musically unnecessary.

Mark Fontana