This is a Gemini rendition (by Retrograde.dk) of the Programmer's Guide to Yamaha YMF 262/OPL3 FM Music Synthesizer by Vladimir Arnost of QA-Software.

Said guide remains an important source of information on programming the historical OPL3 FM chips, but unfortunately it disappeared from the web around May 2024. Luckily, the Wayback Machine had a saved snapshot, which served as the foundation for this version. The colophon of the original web version states:

• HTML Version 1.12 Last Updated Nov-23-2000
• Based on plaintext Version 1.00 Nov-24-1994
• This manual can be distributed freely if not modified.

Gemini version 1.0, Last updated: 2025-10-07

Last good Wayback Machine version

I assume no responsibility for any damages arising out of use or inability to use this text. No warranty is provided about correctness of any information in this file. You are on your own.

• Introduction
• Description of the Synthesizer
• Programming the Synthesizer
• Register Map
• OPL3 Register Reference
• Appendixes
• References

The chip I am going to describe is getting more and more common, but programming information is still scarce, so I have decided to fill in this gap. All information contained in this file is a result of my experience in Adlib programming, research (read: reverse engineering) and finally of my effort to write down everything necessary to understand and use this piece of hardware. No official sources (i.e. development kits, books about this topic, etc.) were available to me except:

Adlib Programming Guide - by Tero Totto, and

The PC Games Programmers Encyclopedia V1.0

The information below is a combination of known features of Adlib (alias Yamaha YM 3812/OPL2) and my own uncountable experiments and failures, which brought out a lot of important details you have to know about the chip.

As far as I know, there are four major sound cards based on OPL3 chip:

• Sound Blaster Pro II (not Sound Blaster Pro I) and many clones
• Sound Blaster 16 and AWE32
• Adlib Gold
• Pro Audio Spectrum Plus/16

I currently have a Sound Blaster Pro II-compatible card only, so all the programming info I provide will be based on this card. (The other cards are quite similar, however. They are just wired at different I/O-port addresses.)

Note: I assume some knowledge of FM music programming (mainly Adlib FM synthesizer) in this manual. If you are new to this topic I recommend you try Adlib first before going higher. Anyway, OPL3 is a direct descendant of OPL2 (what a surprise), so most features of OPL2 are also present on OPL3.

Some basic facts

My card's user manual says: "[this card contains] ... a stereo music FM synthesizer with 20 channels consisting of four (4) operators each ... ". I thought: "Wow -- that's together eighty operators. This must be a GOOD sound-card." I was wrong. Just another advertising lie.

So let's clear some facts. First, OPL3 has only thirty-six (36) operators which can be combined in several ways:

• 18 FM channels (36 operators), or
• 15 FM channels (30 ops) and 5 percussion instruments (6 ops), giving us 20 channels altogether, or
• up to 6 four-operator FM channels (max 24 ops), the rest again being divided into two-operator FM channels and drums.

From the table above you can see that not all channels can be used in four- operator (4-OP) mode -- only a part of the synthesizer is really capable of making 4-OP sounds -- the rest uses traditional two-operator (2-OP) mode.

Second, the manual states this card is capable of "stereo" music. Yes, the quotes are necessary, because the stereo capabilities are very limited. You are given ability to control output going to left or right channel by turning it on and off. That's all. So the sound can flow from very left side, center and very right side. No sound panning, no special stereo effects. :-(

Well, flaming apart, back to the main topic.

Synthesis modes

The OPL3 chip is capable of making sounds in several ways:

Two-operator Additive Synthesis

Output of both operators is simply added. It is the simplest way to make any sound, and it works on both OPL2 and OPL3. The diagram should make it clear.

    +------------+
    |            |
    | Operator 1 +--------+
    |            |        |
    +------------+        |
                  +--------> Output
    +------------+        |
    |            |        |
    | Operator 2 +--------+
    |            |
    +------------+

Two-operator Frequency Modulation (FM) Synthesis

Output from the first operator (Modulator) is sent to the input of the second one (Carrier) and is used to modulate (alter) frequency of the second operator. Only the second operator produces sound. Most of interesting sounds are made this way. This also works on OPL2. Hope the picture helps.

    +------------+         +------------+
    |            |         |            |
    | Operator 1 +-------->| Operator 2 +--------> Output
    |(Modulator) |         | (Carrier)  |
    +------------+         +------------+

Four-operator "Mess" Modulation Synthesis

All of OPL3's 4-OP configurations are combinations of the above two modes of synthesis. OPL3 combines these two modes in four ways. I have no words to describe these four ways. Only the pictures can show their principle.

FM-FM Mode

    +-------+      +-------+      +-------+      +-------+
    |       |      |       |      |       |      |       |
    | Op. 1 +----->| Op. 2 +----->| Op. 3 +----->| Op. 4 +-----> Output
    |       |      |       |      |       |      |       |
    +-------+      +-------+      +-------+      +-------+

AM-FM Mode

    +-------+
    |       |
    | Op. 1 +-----------------------------------+
    |       |                                   |
    +-------+                                   |
                                                |
    +-------+      +-------+      +-------+     |
    |       |      |       |      |       |     |
    | Op. 2 +----->| Op. 3 +----->| Op. 4 +-----+-----> Output
    |       |      |       |      |       |
    +-------+      +-------+      +-------+

FM-AM Mode

    +-------+      +-------+
    |       |      |       |
    | Op. 1 +----->| Op. 2 +-----+
    |       |      |       |     |
    +-------+      +-------+     |
                     +-----> Output
    +-------+      +-------+     |
    |       |      |       |     |
    | Op. 3 +----->| Op. 4 +-----+
    |       |      |       |
    +-------+      +-------+

AM-AM Mode

    +-------+
    |       |
    | Op. 1 +--------------------+
    |       |                    |
    +-------+                    |
                                 |
    +-------+      +-------+     |
    |       |      |       |     |
    | Op. 2 +----->| Op. 3 +-----+-----> Output
    |       |      |       |     |
    +-------+      +-------+     |
                                 |
    +-------+                    |
    |       |                    |
    | Op. 4 +--------------------+
    |       |
    +-------+

Nice, aren't they?

The only way I think this can be written is a math formula. Symbol + (plus) means additive synthesis, and * (asterisk) means frequency modulation (Op1 * Op2 means operator 1 modulates operator 2, not vice versa). Here they are:

• FM-FM Mode: (Op1 * Op2 * Op3 * Op4) ----> Output
• AM-FM Mode: Op1 + (Op2 * Op3 * Op4) ----> Output
• FM-AM Mode: (Op1 * Op2) + (Op3 * Op4) --> Output
• AM-AM Mode: Op1 + (Op2 * Op3) + Op4 ----> Output

Note 1: Actually, modes FM-AM and AM-AM are redundant, because they can be replaced by any pair of 2-OP channels operating at the same frequency. In FM-AM mode, the operator assignment would be straightforward: (Op1, Op2) and (Op3, Op4), both running in FM mode. In the case of AM-AM Mode, a small rearrangement of operators would be necessary: (Op1, Op4) in AM mode and (Op2, Op3) in FM mode.

Note 2: This document uses AM as a shorthand form of Additive Synthesis. Actually this is not any kind of modulation, just a simple addition of two signals. The AM shorthand was chosen as an "obvious" opposite of FM (as seen on your radio receiver). Please note that the OPL2/3 chips are unable to automatically perform any kind Amplitude Modulation other than tremolo effect.

Percussion Mode

In this mode 6 operators are used to produce five different percussion instruments:

• Bass Drum (2 operators)
• Snare Drum (1 operator)
• Tom-Tom (1 operator)
• Cymbal (1 operator)
• Hi-Hat (1 operator)

Because these instruments occupy only three melodic channels, only Bass Drum, Snare Drum and Tom-Tom frequencies can be set. Cymbal and Hi-Hat frequencies are fixed.

This mode is identical with that of OPL2. For more details see ADLIB.DOC.

OPL3 Base Port Assignment

OPL3 may be found at the following addresses:

• 220h or 240h (selectable) and 388h: Sound Blaster Pro II, 16, 32, AWE32/64 and Live,

ESS 688, etc.

• 388h: Adlib Gold, Windows Sound System
• 388h(?): Pro Audio Spectrum Plus/16 (could anyone provide some more info?)

The base address of the synthesizer will be called "base".

OPL3 I/O Ports

The chip occupies four I/O addresses:

• base+0: Primary index register (write), Status register (read)
• base+1: Primary data register (write-only)
• base+2: Secondary index register (write)
• base+3: Secondary data register (write-only)

The index registers are used to select internal registers and data registers are used to write to them. Status register returns the state of two timers built in the chip. OPL3 contains two sets of registers. The Primary set maps to channels 0-8 (operators 0-17) and the secondary maps to channels 9-17 (operators 18-35). The reason for this is simple: all these registers wouldn't fit into single register set.

Unlike Adlib (OPL2), OPL3 doesn't need delay between register writes. With OPL2 you had to wait 3.3 us after index register write and another 23 us after data register write. On the contrary OPL3 doesn't need (almost) any delay after index register write and only 0.28 us after data register write. This means you can neglect the delays and considerably speed up your music driver. But using reasonable delays will certainly do no harm.

The data registers can't be read (they are write-only) on both OPL2 and OPL3.

The registers are grouped in the same manner as in the OPL2 chip. Programs using both OPL2 and OPL3 chips may use the same code provided that their direct I/O interface is well written. The only thing you have to change is operator-to-register mapping, which must accomodate the fact that registers are spread between two register sets.

(The register map is nearly the same so I dared to copy it from ADLIB.DOC.)

Status Register (base+0)

+----------+----------+----------+----------+----------+----------+----------+----------+
|    D7    |    D6    |    D5    |    D4    |    D3    |    D2    |    D1    |    D0    |
+----------+----------+----------+----------+----------+----------+----------+----------+
| IRQFlag  |  T1Flag  |  T2Flag  |                                                      |
+----------+----------+----------+----------+----------+----------+----------+----------+

Empty fields are considered reserved and should not be used or relied upon their value.

Data Registers (base+1, base+3)

+----------+----------+----------+----------+----------+----------+----------+----------+----------+
| Register |    D7    |    D6    |    D5    |    D4    |    D3    |    D2    |    D1    |    D0    |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     01   |                     | WSEnable |                     Test Register                    |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     02   |                          Timer 1 Count (80 usec resolution)                           |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     03   |                          Timer 2 Count (320 usec resolution)                          |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     04*  | IRQReset | T1 Mask  | T2 Mask  |                                | T2 Start | T1 Start |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     04** |                     | 4-OP B-E | 4-OP A-D | 4-OP 9-C | 4-OP 2-5 | 4-OP 1-4 | 4-OP 0-3 |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     05** |                                                                            |   OPL3   |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     08   |   CSW    | Note-Sel |                                                                 |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  20-35   | Tremolo  | Vibrato  | Sustain  |   KSR    |      Frequency Multiplication Factor      |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  40-55   |   Key Scale Level   |                   Output Level (Attenuation)                    |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  60-75   |                Attack Rate                |                 Decay Rate                |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  80-95   |               Sustain Level               |                Release Rate               |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  A0-A8   |                            Frequency Number (Lower 8 bits)                            |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  B0-B8   |                     |  Key-On  |          Block Number          |F-Number (high bits) |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|     BD   | Trem Dep | Vibr Dep | PercMode |  BD On   |  SD On   |  TT On   |  CY On   |  HH On   |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  C0-C8   |                     |  Right   |   Left   |   FeedBack Modulation Factor   |SynthType |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+
|  E0-F5   |                                                      |        Waveform Select         |
+----------+----------+----------+----------+----------+----------+----------+----------+----------+

Notes:  
 *  This register exists only at port base+1
 ** This register exists only at port base+3

For register bases A0, B0 and C0 there is one register per output channel. The primary register set holds the first nine channels (0-8) and the secondary holds last nine channels (9-17).

For bases 20, 40, 60, 80 and E0 there are two registers per channel. Each register maps to one operator. Unfortunately the operator's register numbers are not continuous. The following table shows which operator maps to which register set and offset (in hex).

+-----+------------+  +-----+------------+
| Op. | Set/Offset |  | Op. | Set/Offset |
+-----+------------+  +-----+------------+
|  0  |    0/00    |  | 18  |    1/00    |
+-----+------------+  +-----+------------+
|  1  |    0/01    |  | 19  |    1/01    |
+-----+------------+  +-----+------------+
|  2  |    0/02    |  | 20  |    1/02    |
+-----+------------+  +-----+------------+
|  3  |    0/03    |  | 21  |    1/03    |
+-----+------------+  +-----+------------+
|  4  |    0/04    |  | 22  |    1/04    |
+-----+------------+  +-----+------------+
|  5  |    0/05    |  | 23  |    1/05    |
+-----+------------+  +-----+------------+
|  6  |    0/08    |  | 24  |    1/08    |
+-----+------------+  +-----+------------+
|  7  |    0/09    |  | 25  |    1/09    |
+-----+------------+  +-----+------------+
|  8  |    0/0A    |  | 26  |    1/0A    |
+-----+------------+  +-----+------------+
|  9  |    0/0B    |  | 27  |    1/0B    |
+-----+------------+  +-----+------------+
| 10  |    0/0C    |  | 28  |    1/0C    |
+-----+------------+  +-----+------------+
| 11  |    0/0D    |  | 29  |    1/0D    |
+-----+------------+  +-----+------------+
| 12  |    0/10    |  | 30  |    1/10    |
+-----+------------+  +-----+------------+
| 13  |    0/11    |  | 31  |    1/11    |
+-----+------------+  +-----+------------+
| 14  |    0/12    |  | 32  |    1/12    |
+-----+------------+  +-----+------------+
| 15  |    0/13    |  | 33  |    1/13    |
+-----+------------+  +-----+------------+
| 16  |    0/14    |  | 34  |    1/14    |
+-----+------------+  +-----+------------+
| 17  |    0/15    |  | 35  |    1/15    |
+-----+------------+  +-----+------------+

The following tables summarize which operators form a channel in various modes:

Two-operator Melodic Mode

+------------+--------------------------------------------------------------+
| Channel    | 0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17 |
+------------+--------------------------------------------------------------+
| Operator 1 | 0  1  2  6  7  8  12 13 14 18 19  20  24  25  26  30  31  32 |
| Operator 2 | 3  4  5  9  10 11 15 16 17 21 22  23  27  28  29  33  34  35 |
+------------+--------------------------------------------------------------+

Two-operator Melodic and Percussion Mode

+------------+--------------------------------------------------------------+
| Channel    | 0  1  2  3  4  5  BD SD TT CY HH  9  10 11 12 13 14 15 16 17 |
+------------+--------------------------------------------------------------+
| Operator 1 | 0  1  2  6  7  8  12 16 14 17 13  18 19 20 24 25 26 30 31 32 |
| Operator 2 | 3  4  5  9  10 11 15              21 22 23 27 28 29 33 34 35 |
+------------+--------------------------------------------------------------+

Four-operator Melodic Mode

+------------+---------------------------------------------------+
| Channel    | 0   1   2    6   7   8    9   10  11   15  16  17 |
+------------+---------------------------------------------------+
| Operator 1 | 0   1   2    12  13  14   18  19  20   30  31  32 |
| Operator 2 | 3   4   5    15  16  17   21  22  23   33  34  35 |
| Operator 3 | 6   7   8                 24  25  26              |
| Operator 4 | 9   10  11                27  28  29              |
+------------+---------------------------------------------------+

Channels 3, 4, 5 and 12, 13, 14 can't be used separately because their operators became part of channels 0, 1, 2 and 9, 10, 11 respectively. For instance a four-operator channel 1 consists of two two-operator channels number 1 and 4. (The second 2-OP channel number is always the first 2-OP channel number plus three.)

OPL3 allows you to enable/disable 4-OP mode separately for any of channels 0, 1, 2, 9, 10 and 11 (see register 104h in the reference below). This means for instance when you switch only channel 2 into 4-OP mode, channels number 0, 1, 3, 4, 6, 7, 8, 9, etc. will be still independent 2-OP channels.

Channels 6, 7, 8 and 15, 16, 17 are always two-operator ones. They can't be grouped to form four-operator channels.

Four-operator Melodic and Percussion Mode

+------------+--------------------------------------------------------+
| Channel    | 0   1   2    BD SD TT CY HH    9   10  11   15  16  17 |
+------------+--------------------------------------------------------+
| Operator 1 | 0   1   2    12 16 14 17 13    18  19  20   30  31  32 |
| Operator 2 | 3   4   5    15                21  22  23   33  34  35 |
| Operator 3 | 6   7   8                      24  25  26              |
| Operator 4 | 9   10  11                     27  28  29              |
+------------+--------------------------------------------------------+

Examples

• Two-operator channel #14 consists of operators 26 and 29 which occupy these registers (all are in the secondary register set):

    12A - Operator 1 - Tremolo/Vibrato/Sustain/KSR/Multiplication
    12D - Operator 2 - Tremolo/Vibrato/Sustain/KSR/Multiplication
    14A - Operator 1 - Key Scale Level/Output Level
    14D - Operator 2 - Key Scale Level/Output Level
    16A - Operator 1 - Attack Rate/Decay Rate
    16D - Operator 2 - Attack Rate/Decay Rate
    18A - Operator 1 - Sustain Level/Release Rate
    18D - Operator 2 - Sustain Level/Release Rate
    1A5 -              Frequency Number (low)
    1B5 -              Key On/Block Number/Frequency Number (high)
    1C5 -              FeedBack/Synthesis Type
    1EA - Operator 1 - Waveform Select
    1ED - Operator 2 - Waveform Select

• Four-operator channel #1 consists of operators 1, 4, 7 and 10. All registers except register 104h are in the primary set:

    104 - bit 1 = 1  - Enable Four-Operator Synthesis in channel #1
     21 - Operator 1 - Tremolo/Vibrato/Sustain/KSR/Multiplication
     24 - Operator 2 - Tremolo/Vibrato/Sustain/KSR/Multiplication
     29 - Operator 3 - Tremolo/Vibrato/Sustain/KSR/Multiplication
     2C - Operator 4 - Tremolo/Vibrato/Sustain/KSR/Multiplication
     41 - Operator 1 - Key Scale Level/Output Level
     44 - Operator 2 - Key Scale Level/Output Level
     49 - Operator 3 - Key Scale Level/Output Level
     4C - Operator 4 - Key Scale Level/Output Level
     61 - Operator 1 - Attack Rate/Decay Rate
     64 - Operator 2 - Attack Rate/Decay Rate
     69 - Operator 3 - Attack Rate/Decay Rate
     6C - Operator 4 - Attack Rate/Decay Rate
     81 - Operator 1 - Sustain Level/Release Rate
     84 - Operator 2 - Sustain Level/Release Rate
     89 - Operator 3 - Sustain Level/Release Rate
     8C - Operator 4 - Sustain Level/Release Rate
     A1 -              Frequency Number (low)
     A4 -              Unused
     B1 -              Key On/Block Number/Frequency Number (high)
     B4 -              Unused
     C1 -              FeedBack/Synthesis Type (part 1)
     C4 -              Synthesis Type (part 2)
     E1 - Operator 1 - Waveform Select
     E4 - Operator 2 - Waveform Select
     E9 - Operator 3 - Waveform Select
     EC - Operator 4 - Waveform Select

Note: If a register number is greater than 100h, then it belongs into the secondary register set. (I use this numbering to emphasize the fact that the particular register MUST be written to the secondary set.) See Appendix A.

Status Register

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|IRQ|T1 |T2 |     Not used      |
+---+---+---+---+---+---+---+---+

• bit 7: IRQ Flag. Set whenever any timer has elapsed.
• bit 6: Timer 1 Flag. Set every time the preset time in Timer 1 has elapsed.
• bit 5: Timer 2 Flag. Set every time the preset time in Timer 2 has elapsed.

Timer interrupts are not wired to any IRQ (why??). The timers can be used to detect the OPL2/OPL3 chip (see Appendix B).

Data Registers

01: Test Register / Waveform Select Enable

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|       |WSE|   Test Register   |
+---+---+---+---+---+---+---+---+

• bit 5: Waveform Select Enable. If clear, all channels will use normal sine wave. If set, register E0-F5 (Waveform Select) contents will be used.
• bits 0-4: Test Register. Must be reset to zero before any operation.

02: Timer 1 Count

Upward 8 bit counter with a resolution of 80 usec. If an overflow occurs, the status register bit is set, and the preset value is loaded into the timer again.

03: Timer 2 Count

Same as Timer 1, but with a resolution of 320 usec.

004 (port: base+1): IRQ-Reset / Mask / Start

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|Rst|T1M|T2M|           |T2S|T1S|
+---+---+---+---+---+---+---+---+

• bit 7: IRQ-Reset. Resets timer and IRQ flags in status register. All other bits are ignored when this bit is set.
• bit 6: Timer 1 Mask. If 1, status register is not affected in overflow.
• bit 5: Timer 2 Mask. Same as above.
• bit 1: Timer 2 Start. Timer on/off.
• bit 0: Timer 1 Start. Same as above.

104 (port: base+3): Four-Operator Enable

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|       |ChB|ChA|Ch9|Ch2|Ch1|Ch0|
+---+---+---+---+---+---+---+---+

• bit 5: Enable four-operator synthesis for channel pair 11 - 14 (decimal).
• bit 4: Same as above for channel pair 10 - 13.
• bit 3: Same as above for channel pair 9 - 12.
• bit 2: Same as above for channel pair 2 - 5.
• bit 1: Same as above for channel pair 1 - 4.
• bit 0: Same as above for channel pair 0 - 3.

If reset to zero, OPL3 can produce 18 two-operator sounds at a time.

If nonzero, OPL3 produces four-operator sound in appropriate channel pair.

105 (port: base+3): OPL3 Mode Enable

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|                           |OPL|
+---+---+---+---+---+---+---+---+

• bit 0: OPL3 Mode Enable. When set, OPL3 extensions (36 operators, 4-OP synthesis, 8 waveforms, stereo output) can be used. When reset, the chip behaves as an ordinary OPL2. This bit is zero by default for compatibility with OPL2.

08: CSW / NOTE-SEL

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|CSW|N-S|                       |
+---+---+---+---+---+---+---+---+

• bit 7: Composite sine wave mode on/off. All KEY-ON bits must be clear in order to use this mode. The card is unable to create any other sound when in CSW mode. Unfortunately, I have no info how to use this mode :-< ).
• bit 6: NOTE-SEL. Controls the split point of the keyboard. When 0, the keyboard split is the second bit from the bit 8 of the F-Number. When 1, the MSb of the F-Number is used. (???)

20-35: Tremolo / Vibrato / Sustain / KSR / Frequency Multiplication Factor

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|Tre|Vib|Sus|KSR| Multiplication|
+---+---+---+---+---+---+---+---+

• bit 7: Tremolo (Amplitude vibrato) on/off.
• bit 6: Frequency vibrato on/off.
• bit 5: Sound Sustaining. When 1, operator's output level will be held at its sustain level until a KEY-OFF is done.
• bit 4: Envelope scaling (KSR) on/off. When 1, higher notes are shorter than lower notes.
• bits 0-3: Frequency Multiplication Factor (MULTI). Operator's frequency is set to (see registers A0, B0) F-Number * Factor.

        +-------+--------+
        | MULTI | Factor |
        +-------+--------+
        |   0   |   1/2  |
        |   1   |    1   |
        |   2   |    2   |
        |   3   |    3   |
        |   4   |    4   |
        |   5   |    5   |
        |   6   |    6   |
        |   7   |    7   |
        |   8   |    8   |
        |   9   |    9   |
        |  10   |   10   |
        |  11   |   10   |
        |  12   |   12   |
        |  13   |   12   |
        |  14   |   15   |
        |  15   |   15   |
        +-------+--------+

40-55: Key Scale Level / Output Level

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|  KSL  |      Output Level     |
+---+---+---+---+---+---+---+---+

• bits 6-7: Key Scale Level. Attenuates output level towards higher pitch:

        +-----+-------------+
        | KSL | Attenuation |
        +-----+-------------+
        |  0  | -           |
        |  1  | 1.5 dB/oct  |
        |  2  | 3.0 dB/oct  |
        |  3  | 6.0 dB/oct  |
        +-----+-------------+

• bits 0-5: Output Level. Attenuates the operator output level. 0 is the loudest, 3F is the softest. In additive synthesis, varying the output level of any operator varies the volume of its corresponding channel. In FM synthesis, varying the output level of the carrier varies the volume of the channel. Varying the output of the modulator will change the frequency spectrum produced by the carrier.

The following table summarizes which operators' output levels should be updated when trying to change channel output level.

+-------+------+------+------+------+
| Mode  | Op 1 | Op 2 | Op 3 | Op 4 |
+-------+------+------+------+------+
|  AM   |  +   |  +   | N/A  | N/A  |
|  FM   |  -   |  +   | N/A  | N/A  |
| FM-FM |  -   |  -   |  -   |  +   |
| AM-FM |  +   |  -   |  -   |  +   |
| FM-AM |  -   |  +   |  -   |  +   |
| AM-AM |  +   |  -   |  +   |  +   |
+-------+------+------+------+------+

60-75: Attack Rate / Decay Rate

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|  Attack Rate  |  Decay Rate   |
+---+---+---+---+---+---+---+---+

• bits 4-7: Attack Rate. Determines the rising time for the sound. The higher the value, the faster the attack.
• bits 0-3: Decay Rate. Determines the diminishing time for the sound. The higher the value, the shorter the decay.

80-95: Sustain Level / Release Rate

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
| Sustain Level |  Release Rate |
+---+---+---+---+---+---+---+---+

• bits 4-7: Sustain Level. Determines the point at which the sound ceases to decay and chages to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level. 0 is the softest and F is the loudest sustain level. Note that the Sustain-bit in the register 20-35 must be set for this to have an effect.
• bits 0-3: Release Rate. Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release.

A0-A8: Frequency Number

Determines the pitch of the note. Highest bits of F-Number are stored in the register below.

B0-B8: Key On / Block Number / F-Number(hi bits)

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|       |KEY| Block Num.| Freq  |
+---+---+---+---+---+---+---+---+

• bit 5: KEY-ON. When 1, channel output is enabled.
• bits 2-4: Block Number. Roughly determines the octave.
• bits 0-1: Frequency Number. 2 highest bits of the above register.

The following formula is used to determine F-Number and Block:

F-Number = Music Frequency * 2^(20-Block) / 49716 Hz

Note: In four-operator mode only the register value of Operators 1 and 2 is used, value of Operators 3 and 4 in this register is ignored. In other words: one channel uses only one frequency, block and KEY-ON value at a time, regardless whether it is a two- or four-operator channel.

BD: Tremolo Depth / Vibrato Depth / Percussion Mode / BD/SD/TT/CY/HH On

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|Tre|Vib|Per|BD |SD |TT |CY |HH |
+---+---+---+---+---+---+---+---+

• bit 7: Tremolo (Amplitude Vibrato) Depth. 0 = 1.0dB, 1 = 4.8dB.
• bit 6: Frequency Vibrato Depth. 0 = 7 cents, 1 = 14 cents. A "cent" is 1/100 of a semi-tone.
• bit 5: Percussion Mode. 0 = Melodic Mode, 1 = Percussion Mode.
• bit 4: BD On. KEY-ON of the Bass Drum channel.
• bit 3: SD On. KEY-ON of the Snare Drum channel.
• bit 2: TT On. KEY-ON of the Tom-Tom channel.
• bit 1: CY On. KEY-ON of the Cymbal channel.
• bit 0: HH On. KEY-ON of the Hi-Hat channel.

Note: KEY-ON bits of channels 6, 7 and 8 must be clear and their F-Nums, Attack/Decay/Release rates, etc. must be set properly to use percussion mode.

C0-C8: FeedBack Modulation Factor / Synthesis Type

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|       | R | L | FeedBack  |Syn|
+---+---+---+---+---+---+---+---+

• bit 5: Right Speaker Enable. When set, channel output goes to right speaker.
• bit 4: Left Speaker Enable. When set, channel output goes to left speaker. At least one of these bits must be set to hear the channel.

These two bits can be used to realize sound "panning", but this method offers only three pan positions (left/center/right). These bits apply only to operators producing sound (Carriers). Modulators are not affected by their setting.

• bits 1-3: FeedBack Modulation Factor. If 0, no feedback is present. If 1-7, operator 1 will send a portion of its output back into itself.

        +----------+--------+
        | FeedBack | Factor |
        +----------+--------+
        |    0     |   0    |
        |    1     |  n/16  |
        |    2     |  n/8   |
        |    3     |  n/4   |
        |    4     |  n/2   |
        |    5     |   n    |
        |    6     |  2.n   |
        |    7     |  4.n   |
        +----------+--------+

When in four-operator mode, the FeedBack value is used only by Operator 1, value of Operators 2, 3 and 4 is ignored.

• bit 0: Synthesis Type. 1 = Additive synthesis, 0 = Frequency Modulation

In four-operator mode, there are two bits controlling the synthesis type. Both are the bit 0 of register C0, one of Operators 1 and 2 and the second of Operators 3 and 4.

+--------+--------+--------+
| Op 1&2 | Op 3&4 |  Type  |
+--------+--------+--------+
|    0   |  NONE  |   FM   |
|    1   |  NONE  |   AM   |
|    0   |    0   | FM-FM  |
|    1   |    0   | AM-FM  |
|    0   |    1   | FM-AM  |
|    1   |    1   | AM-AM  |
+--------+--------+--------+

E0-F5: Waveform Select

+-7-+-6-+-5-+-4-+-3-+-2-+-1-+-0-+
|                   | WaveForm  |
+---+---+---+---+---+---+---+---+

• bits 0-2: WaveForm Select (WS):

WaveForm 0: Sine

WaveForm 1: Half-Sine

WaveForm 2: Abs-Sine

WaveForm 3: Pulse-Sine

WaveForm 4: Sine (even periods only)

WaveForm 5: Abs-Sine (even periods only)

WaveForm 6: Square

WaveForm 7: Derived Square

Note: Bit 5 of register 01 must be set to use waveforms other than sine. Waveforms 4-7 are available only on OPL3.

Appendix A - Examples

These examples show a few working routines used in my MUS Player. They are written in Borland C++ 3.1 but should be easy to translate to any other language.

--------------------------------- cut here ---------------------------------
// I prefer using these Assembler-like types
typedef unsigned int  WORD;
typedef unsigned char BYTE;

/*
 * FM Synthesizer base port. SB Pro II - 0x220, Adlib 0x388
 */
WORD FMport = 0x220;

/*
 * Enables OPL3 extensions.
 */
WORD OPL3 = 1;

/*
 * Direct write to any Adlib/SB Pro II FM synthetiser register.
 *   reg - register number (range 0x001-0x0F5 and 0x101-0x1F5). When high byte
 *         of reg is zero, data go to port FMport, otherwise to FMport+2
 *   data - register value to be written
 */
BYTE FMwriteReg(WORD reg, BYTE data)
{
    asm {
        mov dx,FMport
        mov ax,reg
        or  ah,ah       // high byte is nonzero -- write to port base+2
        jz  out1
        inc dx
        inc dx
    }
out1: asm {
        out dx,al
        mov cx,6
    }
loop1: asm {            // delay between writes
        in   al,dx
        loop loop1

        inc dx
        mov al,data
        out dx,al
        dec dx
        mov cx,36
    }
loop2: asm {            // delay after data write
        in   al,dx
        loop loop2
    }
    return _AL;
}

/*
 * Write to an operator pair. To be used for register bases of 0x20, 0x40,
 * 0x60, 0x80 and 0xE0.
 */
void FMwriteChannel(BYTE regbase, BYTE channel, BYTE data1, BYTE data2)
{
    static BYTE adlib_op[] = {0, 1, 2, 8, 9, 10, 16, 17, 18};
    static BYTE sbpro_op[] = { 0,  1,  2,   6,  7,  8,  12, 13, 14,
                  18, 19, 20,  24, 25, 26,  30, 31, 32};
    static WORD rg[] = {0x000,0x001,0x002,0x003,0x004,0x005,
            0x008,0x009,0x00A,0x00B,0x00C,0x00D,
            0x010,0x011,0x012,0x013,0x014,0x015,
            0x100,0x101,0x102,0x103,0x104,0x105,
            0x108,0x109,0x10A,0x10B,0x10C,0x10D,
            0x110,0x111,0x112,0x113,0x114,0x115};

    if (OPL3)
    {
        register WORD reg = sbpro_op[channel];
        FMwriteReg(rg[reg]+regbase, data1);
        FMwriteReg(rg[reg+3]+regbase, data2);
    } else {
        register WORD reg = regbase+adlib_op[channel];
        FMwriteReg(reg, data1);
        FMwriteReg(reg+3, data2);
    }
}

/*
 * Write to channel a single value. To be used for register bases of
 * 0xA0, 0xB0 and 0xC0.
 */
void FMwriteValue(BYTE regbase, BYTE channel, BYTE value)
{
    static WORD ch[] = {0x000,0x001,0x002,0x003,0x004,0x005,0x006,0x007,0x008,
            0x100,0x101,0x102,0x103,0x104,0x105,0x106,0x107,0x108};
    register WORD chan;

    if (OPL3)
        chan = ch[channel];
    else
        chan = channel;
    FMwriteReg(regbase + chan, value);
}
--------------------------------- cut here ---------------------------------

Appendix B - Detection Methods

OPL2 Detection

An official method of Adlib (OPL2) detection is:

• Reset Timer 1 and Timer 2: write 60h to register 4.
• Reset the IRQ: write 80h to register 4.
• Note: Steps 1 and 2 can't be combined together.
• Read status register: read port base+0 (388h). Save the result.
• Set Timer 1 to FFh: write FFh to register 2.
• Unmask and start Timer 1: write 21h to register 4.
• Wait in a delay loop for at least 80 usec.
• Read status register: read port base+0 (388h). Save the result.
• Reset Timer 1, Timer 2 and IRQ as in steps 1 and 2.
• Test the results of the two reads: the first should be 0, the second should be C0h. If either is incorrect, then the OPL2 is not present.

Notes:

• You should AND the result bytes with E0h because the unused bits are undefined.
• This testing method doesn't work in some SoundBlaster compatible cards.

OPL3 Detection

• Detect OPL2. If present, continue.
• Read status register: read port base+0.
• AND the result with 06h.
• If the result is zero, you have OPL3, otherwise OPL2.

Note: This is NOT an official method. I have dug it out of a sound driver. I haven't tested it, because I haven't an OPL2 card (Adlib, SB Pro I). Nevertheless it "detects" my SB Pro II properly. ;-)

Another possible detection method for distinguishing between SB Pro I and SB Pro II would be to try to detect OPL2 at I/O port base+0 and then at port base+2. The first test should succeed and the second should fail if OPL3 is present. (Remember: SB Pro I contains twin OPL2 chips at addresses base+0 and base+2, while SB Pro II contains one OPL3 chip at I/O address base+0 thru base+3).

The BLASTER Environment Variable

Perhaps the most recommended "detection" method. Reading this variable avoids blindfold I/O port scanning and possible device conflicts. The user is responsible for its proper setting.

The variable has this format:

BLASTER=Aaddr Iirq Ddma8 Hdma16 Pmidi Eemu Ttype

A: Base I/O address given in hex. For most Sound Blasters the default is 220.
I: IRQ Number (decimal). Default 7 (old SB and SB Pro), 5 (SB 16, etc.).
D: DMA Number (decimal). Default 1.
H: High DMA Number (decimal). Default 5 (on SB 16 and newer cards only)
P: MPU-401 MIDI port (hexadecimal). Default 330 (on SB 16 and newer cards)
E: EMU-8000 base port (hexadecimal). Default 620 (on AWE32 and newer cards)
T: Card Type (decimal):
    1 - Sound Blaster 1.5 
    2 - Sound Blaster Pro I 
    3 - Sound Blaster 2.0 
    4 - Sound Blaster Pro II 
    6 - Sound Blaster 16/AWE 32/32/64 

Examples:

• BLASTER=A220 I7 D1 T4 (old 8-bit Sound Blaster Pro II)
• BLASTER=A220 I5 D1 H5 P330 E620 T6 (16-bit Sound Blaster 32)

Title:      The PC Games Programmers Encyclopedia
Authors:    Mark Feldman and many others on Usenet and Internet
WWW:        http://www.qzx.com/pc-gpe/
FTP:        ftp://x2ftp.oulu.fi/pub/msdos/programming/gpe/pcgpe10.zip - 700KB

... you can find (almost) everything you need there

Title:      Sound Blaster - The Official Book
Authors:    Richard Heimlich, David M. Golden, Ivan Luk, Peter M. Ridge
Publishers: Osborne/McGraw Hill
ISBN:       0-07-881907-5

... this is a number-one in my book-wishlist. If anyone wanted to get rid of the book, I wouldn't scorn it ... :-)

Title:      The SoundBlaster Developer Kit
Publishers: Creative Labs Inc
            Creative Technology PTE LTD

... I wonder if you can find something comprehensible in that.