Sound

Sound hardware in DOS games is programmed directly. A game's music may exist only as commands to a synthesiser chip. Its timing may come from the sound card's interrupts. To reproduce the sound exactly, you need to know which device the game wrote for and how it drove it.

The devices

Device	Year	How games use it	Notes
PC speaker	1981	Tones from timer channel 2 (port 42h), switched on through port 61h	Some games played samples by switching the speaker very fast
IBM PCjr and Tandy 1000	1984	TI SN76496 tone/noise registers; some Tandy models use NCR 8496 or PSSJ audio	Common in early DOS games and ports; later PSSJ adds an 8-bit DAC
Covox Speech Thing and Disney Sound Source	1987	8-bit samples written through an LPT port	The Disney device adds a FIFO; both can be driven by software timing
Creative Music System / Game Blaster	1987	Two Philips SAA1099 chips	Square-wave voices, noise and stereo
AdLib	1987	The Yamaha YM3812 (OPL2) FM chip at ports 388h and 389h	9 voices of FM synthesis; music is a stream of register writes
Roland MT-32	1987	MIDI through an MPU-401 interface (port 330h)	Its own synthesis and sounds; many Sierra games were written for it
Sound Blaster	1989	An OPL2 for music, and an 8-bit digital channel (the DSP) with DMA	Settings in the BLASTER environment variable: port, IRQ, DMA
Sound Blaster Pro	1991	SB Pro 1 uses two OPL2 chips; SB Pro 2 uses the YMF262 OPL3	Both provide stereo PCM
Sound Blaster 16 and AdLib Gold	1992	SB16 adds 16-bit DMA; AdLib Gold adds stereo and a digital section	OPL3 implementations vary across card revisions
Pro AudioSpectrum, Windows Sound System and ESS AudioDrive	1991 onward	16-bit PCM through a codec; models vary in OPL3, Sound Blaster compatibility and mixer support	Identify the exact card and codec
Gravis Ultrasound	1992	32 hardware voices playing samples from the card's own memory	Popular with tracker music and the demo scene
General MIDI modules (Roland SC-55)	1991	MIDI through an MPU-401	General MIDI fixed the instrument numbers
AWE32/AWE64	1994	Sound Blaster PCM plus EMU8000 wavetable voices and uploaded banks	Games may use the SoundFont Manager as well as midiOut
Aureal A3D and Creative EAX	1997–1998	DirectSound 3D extensions for positional audio and environmental effects	APIs differ: A3D exposes COM interfaces; EAX uses DirectSound property sets

Creative Music System and Game Blaster

The CMS/Game Blaster uses two Philips SAA1099 chips. Each chip provides six square-wave channels, two noise generators, two envelope controllers and stereo amplitude registers. The gameframe-saa1099 crate models the chip registers and the four-port card window. Its port map and default address come from static traces of CMSDRV.COM and Sierra's CMS35.BIN; register timing follows Philips's data handbook and its SAA1099 article. The model includes the common CMS detection-port response reported by a compatible-card manual. The noise seed, combined tone/noise gate, full custom-chip behavior, bus waits and analog output still have software-only follow-up checks. See the CMS/SAA1099 evidence and check plan.

PCjr and Tandy 1000 PSG

The IBM PCjr and original Tandy 1000 use the TI SN76496 for three tone channels and one noise channel. The gameframe-sn76496 crate models the serial register protocol, input-clock advancement, sample generation and the PCjr four-source output mux selected by port 61h bits 5–6. The Tandy adapter maps writes at C0h–C7h, routes PIT channel 2 to the chip's AUDIO IN pin and exposes the service manual's approximate 42 CPU wait states. Static traces of Sierra's original JR.DRV and TANDY.DRV confirm tone latch/data writes, attenuation writes, startup mutes and PSG-output selection. The Tandy external-output mux routes PIT channel 2, bus Audio In or the complex sound generator using its documented 00b, 10b and 11b selections; the fourth input remains unidentified. Tandy 1000 HX documentation identifies an NCR 8496, while later PSSJ machines add an 8-bit DAC. Those variants, noise feedback details, period-zero behavior and analog output still need software-only comparisons. See the Tandy PSG findings and check plan.

FM synthesis (OPL2 and OPL3)

Music for AdLib and Sound Blaster is a stream of writes to the chip's registers: which voice, which frequency, which instrument settings, key on and key off. The chip turns these into sound.

• Capture the register writes, with the time of each, from the original running in an emulator. This is exact ground truth for the music code, independent of the chip.
• Port the music driver so it produces the same writes at the same times. Compare the two lists write by write.
• Emulate the chip in the port to turn writes into samples. gameframe-opl2 covers the YM3812, including CSM speech mode and its timer-triggered key pulses. gameframe-opl3 models both YMF262 register banks, two- and four-operator voices, four sample outputs, OPL2 compatibility mode, shared note selection, timers and indexed ports. Its status signature stays distinct from the YM3812 in compatibility mode, and it omits the YM3812's CSM feature. The original AdLib Gold GSSOPL3.DRV binary documents its banked writes, busy polling, second data-port reads and setup of registers 0x104 and 0x105 (trace). The Ad Lib Gold Developer Toolkit identifies the second-bank 0xFF/0xFE switches as Control Chip access and documents its status and registers. gameframe-adlib-gold models that port overlay and register interface around gameframe-opl3. The chip model follows Yamaha's datasheet through its serial DAC interface. gameframe-yac512 models the external DAC's serial input, FSEL decoding and sample latches. gameframe-ymz263 models the AdLib Gold's digital PCM/ADPCM channels, FIFOs, timers, DMA request state and MIDI UART. The card routes the MMA ports and sampling interrupt. YMZ263 ADPCM rounding, interleave and some status details still need a software comparison. Independent carrier routing in four-operator mode, output parity, YAC512's floating analog transfer, AdLib Gold analog mixer/filter behavior and analog input paths remain open.
• The driver's tempo usually comes from a timer interrupt the game programmed. Find the interrupt rate and the driver's tick counter. Small errors in the rate change the music's speed over a song.

Digital sound (Sound Blaster DSP)

The game sets up a DMA transfer from a buffer to the card and tells the card's DSP the sample rate. When the buffer has played, the card raises an interrupt. The game then refills the buffer.

• Sample rates are set as a "time constant": 256 - 1,000,000 / rate. The real rate is the rate that constant gives, which is not exactly the rate the game asked for. Compute it.
• Games mix several effects into one buffer in software. If the sound must match, port the mixer's volume scaling and clipping exactly. Games of 1997 to 1999 often had a second, MMX mixer that scales with pmulhw and clips with paddsw, and its samples can differ from the plain build's (SIMD code).
• If the game counts sound interrupts to time anything, that count is an input.

MIDI

MIDI music is a list of note and controller events, often stored in a game's own format or as standard MIDI files. The sound depends entirely on the synthesiser. The same music sounds very different on an MT-32, a Sound Canvas and a Sound Blaster's FM.

• Port the MIDI player: the events and their timing must be exact.
• Play the events through a software synthesiser with sounds of the reference device (an MT-32 emulator such as Munt, or General MIDI sound fonts).
• MT-32 games often upload their own instrument settings to the device at start-up with SysEx messages. Capture and replay them.

Sound drivers in DOS games

Many games used a sound library instead of programming cards themselves: the Miles Audio Interface Library, DIGPAK and MIDPAK, the HMI Sound Operating System. Each loads a driver for the player's card. Label the library and port what the game asks of it: play this sample, play this song, set this volume (Middleware).

Windows sound

API	Year	Notes
WinMM (waveOut, midiOut)	1991	Simple and with high latency
DirectSound	1995	Mixing by the system or the card; 3D sound from DirectX 3
DirectMusic	1999	Music with styles and segments that change with the game
A3D (Aureal)	1997	Positional 3D sound in hardware
EAX (Creative)	1998	Reverb and environment effects on top of DirectSound 3D

A3D and EAX effects need hardware that no longer exists. Software reimplementations exist (OpenAL Soft supports EAX effects). Decide whether the port reproduces them and record it. The sound card makers' APIs covers these and the other card libraries of the time, and the stand-ins in wrappers/. PC audio coverage tracks which devices and APIs GameFrame can reuse today and which reusable pieces remain to build.

Checklist

1. Find which devices the game supports, from the setup program and the drivers it ships.
2. Choose the reference device and write it in the project's AGENTS.md.
3. Find the timer or interrupt that drives the music, and its rate.
4. Capture the music's register writes or MIDI events from the original, with times.
5. Port the music driver and compare the events. Then compare the audio.