Adlib Patch Resource Format                                        Revision 1
Ravi I.                                                         Mar. 11, 2002


Preface

   The Adlib patch resource defines instruments for the Yamaha OPL2 FM
   synthesis chip. Other cards, including the original SoundBlasters, that had
   the same or compatible chips also used the Adlib patch. The patch is
   traditionally numbered PATCH.004 or 4.PAT.

   Sierra does not seem to have changed the format of its Adlib patch resource
   through the entire life of SCI. This file format applies to all IBM games.

   Please post comments or questions to the SCI webboard:
      http://pub48.bravenet.com/forum/show.asp?usernum=4071584210

   More SCI information is available on the WWW at
      http://freesci.linuxgames.com     The FreeSCI Project Homepage
      http://agisci.cjb.net             The Ultimate AGI & SCI Web Site

   The latest version of this specification should be available at
      http://www4.ncsu.edu/~rniyenga/

   You can contact me personally at ravi.i@softhome.net, but I would prefer
   that SCI messages be posted on the webboard so everyone can see them.


File Format

   The first two bytes of an extracted patch file contain the bytes 89h 00h
   identifying a patch resource. These are not actually part of the resource
   data.

   Patch files contain a block of 48 instrument definitions followed
   optionally by the magic number ABh CDh (CDABh when read into a little
   endian machine) and 48 more definitions. Each instrument definition is
   28 bytes containing data for an Adlib channel composed of two operators.


Instrument Definitions

   An instrument definition has the following fields, each 1 byte long:

     offset  |        description        |    values
   ----------+---------------------------+--------------
       0h    | op 1 key scaling          | 0 - 3
       1h    | op 1 frequency modulation | 0 - 15
       2h    | channel feedback          | 0 - 7
       3h    | op 1 attack rate          | 0 - 15
       4h    | op 1 sustain level        | 0 - 15
       5h    | op 1 envelope generator   | true, false
       6h    | op 1 decay rate           | 0 - 15
       7h    | op 1 release rate         | 0 - 15
       8h    | op 1 amplitude            | 0 - 63
       9h    | op 1 amplitude modulation | true, false
       Ah    | op 1 vibrato              | true. false
       Bh    | op 1 keyboard scale rate  | true, false
       Ch    | algorithm (reversed)      | 0, 1
       Dh    | op 2 key scaling          | 0 - 3
       Eh    | op 2 frequency modulation | 0 - 15
       Fh    |    unused                 |
      10h    | op 2 attack rate          | 0 - 15
      11h    | op 2 sustain level        | 0 - 15
      12h    | op 2 envelope generator   | true, false
      13h    | op 2 decay rate           | 0 - 15
      14h    | op 2 release rate         | 0 - 15
      15h    | op 2 amplitude            | 0 - 63
      16h    | op 2 amplitude modulation | true, false
      17h    | op 2 vibrato              | true. false
      18h    | op 2 keyboard scale rate  | true, false
      19h    |   unused                  |
      1Ah    | op 1 waveform             | 0 - 3
      1Bh    | op 2 waveform             | 0 - 3

   Note that the sense of the algorithm field is switched. A value of 0 means
   that the two operators are in synthesis while a value of 1 means that
   operator 1 modulates operator 2.


Revision history

   Revision 1 - Mar. 11, 2002
      - First release of the specification