MIDICraft's MIDINET CD-ROM/MIDICraft's MIDINET CD-ROM.iso/DOCS/MT32NTRN.ZIP/MT32NTRN.TXT

Internet Message Format | 1991-06-05 | 9.0 KB

From ucsd!rutgers!gatech!cwjcc!tut.cis.ohio-state.edu!mailrus!cornell!
batcomputer!itsgw!steinmetz!ge-dab!ge-rtp!edison!mfs Sun  Jan  22  07:21:36
PST 1989
Article 3957 of rec.music.synth:
Path: ucsd!rutgers!gatech!cwjcc!tut.cis.ohio-state.edu!mailrus!cornell!
batcomputer!itsgw!steinmetz!ge-dab!ge-rtp!edison!mfs
>From: [e-mail] (Martin @ I was a plant in a previous life)
Newsgroups: rec.music.synth
Subject: The MT-32
Keywords: the guts of the machine
Message-ID: <[e-mail]>
Date: 18 Jan 89 22:19:20 GMT
Lines: 152


Ah, the MT-32; a great little  box  -  for  the money.  I dearly love mine,
even though it is kind of noisy.  I  have gotten a lot of requests for info
on the MT, so I will attempt to  share  what  I know about it. Most of this
info also applies to the D110, except  the D110 has more reverb modes, more
PCM samples, battery backup, a card slot, and killer drum samples.

First, the obvious.  The  MT  is  a  multi-timbral  sound  module that uses
Roland's now famous (infamous ?) sound  generation method called LA (Linear
Arithmetic) synthesis.  This is really  just  a  fancy  name for mixing PCM
samples with  'normal'  sawtooth/square  wave  kinds  of  sounds  While the
timbres produced by the LA method  sound complex, programming the sounds is
actually rather easy.

Of course, to change any of  the  MT's  parameters, you need a computer and
the proper software; there are only  a  few  things you can change from the
front panel.

The MT is logically divided  into  several  sections.   First are the synth
parts.  There are 8  of  these,  each  of  which  has  its own MIDI channel
number, volume and pan setting.  Kind of  like  8 synths and a mixer in one
box.

The next section is the drum  section.   This  area  allows you to assign a
canned rhythm sound or  any  sound  loaded  into  RAM  to a particular note
number.  You can also set the pan, volume and turn the reverb on or off for
each of these sounds.

Now, all of the synth parts  and  the  drum  section  draw from a 'pool' of
sounds arranged in banks of 64.  There are two banks of 'musical' sounds in
ROM (A and B), one bank of 'drum' sounds in ROM (actually only 30 of these,
abbreviated R) and one bank of RAM sound locations (called M for memory).

You can get to the ROM A and  B  sounds  in  two ways.  The first way is to
select a part button and spin  the  knob.   The  little micro inside the MT
dutifully loads the sounds into the part  as  the knob goes round.  You can
also use MIDI program change commands  to  pull  up the sounds.  There is a
difference tho, 'cause when you use the  program change commands to pull up
a sound, the MT uses an area called the patch map to get to them.

The patch map is an area of 128 locations, each of which corresponds to one
of the 128 possible MIDI  program  change  numbers.   Each entry in the map
specifies a bank (A,B,R or M) and a  number (1-64).  When you power up your
MT, this map is defaulted so that  program change numbers 1-64 will 'point'
to ROM bank A and numbers  65-128  point  to  bank B.  Using a computer and
editor, you can change these map entries to point to any sound in any bank.
And, not only can you specify  the  bank  and  sound number, each map entry
allows you to specify  the  bend  range,  the  keyshift (in semitones), the
polymode (whether the next note on cuts off the previous note or triggers a
new one) and the whether the reverb is  on or off.  Note that there is only
one patch map.  If you  send  a  program  change  to  one part on a certain
channel and then send the same  program  change the another part on another
channel, they will both  be  set  according  to  that  particular patch map
entry.

The last group is the system section  which controls the global things such
as master volume, tuning and the reverb.   The MT has four kinds of reverb:
room, hall, plate and discrete echo.  You  can set the reverb time from 1-8
and the level from 0 to 7.  Note that  the reverb on the MT is global.  You
can turn the reverb on or off  for  each  part or drum sound, but you can't
have one part set to one thing and another part set to something else.

So all in all the MT is really  very flexible in terms of setting things up
and pulling up  sounds  via  MIDI.   Now  I  will  try  to  break  down the
parameters that make up a sound.

The smallest unit of sound generation  is  called a partial.  Four partials
are grouped together to form a  timbre.   You  can  make a timbre using all
four partials if you want, or  you  can  use  just  one or two.  There is a
section of the  timbre  refered  to  as  the  common  parameters. This area
contains the 'switches' to turn on or off  any of the four partials and the
partial structures  (see  below)   All  together  the  MT  can  generate 32
partials at any one instant.   These  are all dynamically allocated between
the synth and drum parts.

Let's look at a partial.   Each  one  of  these  is  made  up of a Waveform
Generator (WG), Time Variant  Filter  (TVF)  and  a  Time Variant Amplifier
(TVA).  Each of  these  blocks  has  several  parameters  and  a five stage
envelope generator associated with it.   The  WG  has controls which affect
the coarse and fine pitch, select the  waveform (sawtooth, square or PCM #)
and control the amount  of  envelope  effect.   The  TVF parameters include
cutoff  frequency,  resonance,  velocity   sensitivity,  several  keyfollow
parameters and a five  stage  envelope  generator  (the  last  stage of the
envelope is fixed as the sustain level  and  release time).  The TVA has an
overall level  adjustment,  velocity  sensitivity  controls,  a  five stage
envelope and two programmable keyfollow controls.

Partials can be one of  two  types:  Synth  or  PCM partials.  In the Synth
partials, all of the above mentioned blocks  are  active.  You can set up a
sawtooth on the WG, filter it with  the  TVF and adjust the volume with the
TVA.  In a PCM partial, instead  of  using  the standard square or sawtooth
kind of waveform, a sampled  waveform  is  selected.  Some of these samples
are looped so they  sustain,  while  others  only  sound during the initial
attack of a note.  Also, in a PCM partial, the TVF has no effect.

As mentioned above, partials are combined into blocks called timbres.  Each
timbre is made up of two  pairs  of  partials.  These pairs are combined by
setting a parameter called a  structure.   The structure tells the partials
what kind they are   (Synth  or  PCM)  and  how  their  output is combined.
Depending on the structure setting, the partials  can  be set up as 2 synth
partials, a PCM  partial  and  a  synth  partial,  2  PCM  partials, stereo
PCM/synth partials (one partial out  the  left  and  one out the right) and
ring modulated synth and/or PCM partials.  (13 all total) Very flexible.  I
should note here that the MT firmware  has  a  bug which does not allow the
volume to be  controlled properly if structures 10-13 are used. (Maybe this
is just a H/W limitation)

Now for the MT insides:

The MT-32 uses an Intel 8097  microcontroller  as  the  main CPU.  It has a
total of 64K of ROM and 32K of RAM.   The RAM is not battery backed, so you
have to reload all of your sounds and  the patch map when you power up. The
CPU (and the operating system in  the  ROMs) controls the custom LA32 chip.
The LA chip has connections for  the  PCM  sample ROMs (two 256Kx8  Toshiba
Mask ROMs on board rev 0 or one Hitachi  512Kx8 ROM on board rev 1) and the
digital reverb chip.  Contrary to  popular  opinion,  the LA chip sends all
it's data to the reverb chip  in  digital  format, not in analog form.  The
data is routed to the D/A converter  (a  BurrBrown PCM54 chip) and out to 6
sample/hold chips.  With a few exceptions, this is the same circuitry as in
the D110.  (And probably the D10 and 20,  but  I don't have them so I can't
look inside)  For some reason, one of  the  data  lines from the LA chip to
the D/A is LEFT OFF, killing the S/N  ratio.   Also, (as near as I can tell
with the trusty 1240 logic analyzer)  the  sample  data  in the ROMs has no
data for this bit.  Note that the  D110  runs  ALL 16 bits to the D/A which
explains its better S/N ratio.

-------------------------------------------------------------------------

Oh well, I'm busy trying to find a  way  to quiet my MT down by running the
extra line and using a slightly better D/A, but so far, no luck.  I am also
gonna try putting a D110 PCM sample ROM in the MT to see if that will work.
I've managed to dissassemble all the  code  in  the  ROMs and I hope to get
some simple front panel editing functions  in there.  (Not that easy!) And,
I'm workin' on a battery backup circuit and a 500+ EPROM sound bank.

I also have new EPROMs available wich  have 128 new sounds in them.  Unlike
the aforementioned products,  these  are  done  and  work  quite well. (The
sounds are MUCH better than the originals  too)  Of course you will have to
install sockets in your MT, as only  the  first  20000 or so were sold with
socketed EPROMs.....  Oh well.   Write or Email for more info -


Martin

[e-mail]

BLUE RIDGE MUSIC SOFTWARE
Rt 8, Box N55,
Charlottesville, VA 22901