View source for Adlib Patch Resource Format Specification

Revision 1<br />
Ravi I.<br />
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.
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===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:
{| cellpadding="2" cellspacing="0" border="1"
! offset || description || values
|-
| align="center" | 0h || op 1 key scaling || align="center" | 0 - 3
|-
| align="center" | 1h || op 1 frequency modulation || align="center" | 0 - 15
|-
| align="center" | 2h || channel feedback || align="center" | 0 - 7
|-
| align="center" | 3h || op 1 attack rate || align="center" | 0 - 15
|-
| align="center" | 4h || op 1 sustain level || align="center" | 0 - 15
|-
| align="center" | 5h || op 1 envelope generator || align="center" | true, false
|-
| align="center" | 6h || op 1 decay rate || align="center" | 0 - 15
|-
| align="center" | 7h || op 1 release rate || align="center" | 0 - 15
|-
| align="center" | 8h || op 1 amplitude || align="center" | 0 - 63
|-
| align="center" | 9h || op 1 amplitude modulation || align="center" | true, false
|-
| align="center" | Ah || op 1 vibrato || align="center" | true. false
|-
| align="center" | Bh || op 1 keyboard scale rate || align="center" | true, false
|-
| align="center" | Ch || algorithm (reversed) || align="center" | 0, 1
|-
| align="center" | Dh || op 2 key scaling || align="center" | 0 - 3
|-
| align="center" | Eh || op 2 frequency modulation || align="center" | 0 - 15
|-
| align="center" | Fh || unused || align="center" | &nbsp;
|-
| align="center" | 10h || op 2 attack rate || align="center" | 0 - 15
|-
| align="center" | 11h || op 2 sustain level || align="center" | 0 - 15
|-
| align="center" | 12h || op 2 envelope generator || align="center" | true, false
|-
| align="center" | 13h || op 2 decay rate || align="center" | 0 - 15
|-
| align="center" | 14h || op 2 release rate || align="center" | 0 - 15
|-
| align="center" | 15h || op 2 amplitude || align="center" | 0 - 63
|-
| align="center" | 16h || op 2 amplitude modulation || align="center" | true, false
|-
| align="center" | 17h || op 2 vibrato || align="center" | true. false
|-
| align="center" | 18h || op 2 keyboard scale rate || align="center" | true, false
|-
| align="center" | 19h || unused || align="center" | &nbsp;
|-
| align="center" | 1Ah || op 1 waveform || align="center" | 0 - 3
|-
| align="center" | 1Bh || op 2 waveform || align="center" | 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

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[[Category:SCI_Driver_Resources]]
[[Category:Audio]]