Vmap 1.1 (March 10, 1993)
=========================

Phat Tran

INTRODUCTION

Normally, MIDI files written for Roland soundcards will sound strangely
mute on the Gravis Ultrasound (GUS), with some tracks playing much
softer than others.  This is because the volume response of the GUS is
exponential whereas that of the Rolands is linear.  The loudness vs.
volume setting plot for each type of card is shown below:

              |                                   /
              |                                 / *
  Perceived   |                               /   *
  Loudness    |                             /     *
              |                           /      *
              |                         /        *
              |                       /          *
              |                     /           *
              |                   /             *
              |                 /              *
              |               /               *
              |             /               **
              |   Roland  /               **
              |         /               **
              |       /              ***   GUS
              |     /           ****
              |   /        ****
              | /********
              +------------------------------------
              0                                  127
                          Volume Setting

What vmap does is remap the volume changes and key velocities in the
MIDI file so that the notes will play with the same relative volume
on the GUS as on the Rolands.  The formula used is:

                   V' = log(V + 1) * 127 / log(128)

A remapped Roland file will sound "fuller" on the GUS than the original
would.

This mismatched volume problem goes both ways...  MIDI files composed
for the GUS will sound dinly loud on the Rolands, with background tracks
overwhelming the foreground.  Vmap 1.1 will also let you remap the
volume changes and key velocities of GUS .mids for Rolands.

INSTRUCTIONS

To use vmap, invoke it at the command line as follows:

    vmap [-r] [-t] <in.mid> <out.mid>

Vmap will then process <in.mid> and output the result as <out.mid>.  (Of
course, you would substitute your own filenames for <in.mid> and
<out.mid>.  They must not be the same file.)

Vmap will also display the MIDI and track headers, and any text it finds
in the file.

The default operation is a Roland to GUS remapping, but the -r (Roland)
switch will tell vmap to convert GUS MIDI files to Roland.  Resolution
will be lost due to rounding, so don't convert files back and forth
between Roland and GUS more than necessary.

The -t (test) switch will tell vmap to go through the motions of
remapping <in.mid>, but without outputting to a file.  Thus, you need
not specify <out.mid>.

BUGS

Vmap has not been tested very thoroughly, so there may be bugs that will
crop up as the program is exposed to .mids more exotic than the ones I
have to test it with.  Bug reports and/or comments can be sent to
my Internet account (ptran@sciborg.uwaterloo.ca).  Particulary, if vmap
reports "Unexpected EOF." when processing a .mid file that you know is
intact, tell me!  There may be several MIDI messages that I don't know
about which can cause vmap to lose its framing.

REVISIONS

Version 1.0 -- Original release.

Version 1.1 -- New features:
               - GUS to Roland remapping
               - test mode
               - text dump