The Developer's Tidbits

Helpful tips for random problems
The skyline of Sydney, Australia - used as a header image for aesthetics
The skyline of Sydney, Australia - used as a header image for aesthetics


DOSBox sound emulation

Reading time for 3919 words - 20 minutes

Sound hardware was probably one of the more complex and irritating elements of DOS gaming in the early 1990’s. So many choices, incompatibilities and even different advantages for sound effects, speech or music. So what do you choose today when an emulator like DOSBox gives you so many audio choices?

Well this entry will describe the major sound cards that impacted the DOS era of PC gaming, a brief history and their compatibility with DOSBox. I will also create a chart that will list in my opinion the best music and sound effect emulation options for your gaming titles.


PCM – Pulse Code Modulation, is a digital representation of an analogue sample, also used by audio CDs and occasionally on DVDs.

DAC – Digital to Analogue Converter, used for playing back digital sound and music through standard speakers and headphones.

ADC – Analogue to Digital Converter, used for recording samples from a standard microphone and storing it in a digital format on the computer.

DSP – Digital Signal Processing or Processor, essentially it is DAC and ADC combined meaning it allows for both digital to analogue playback and analogue to digital recording. channel – A single music instrument or sound sample.

FM synthesis – Frequency Modulation synthesis, generates and distorts an audio tone to fake an instrument, often used on synthesises from the 1980’s or earlier and has a very electronic, artificial sound.

LA synthesis – Linear Arithmetic synthesis, uses filters to manipulate pre-recorded digital sample sounds.

Wave-table synthesis – In PC audio it refers to pre-recorded sounds and samples or instruments that are then manipulated for tone and pitch.

PC speaker

1 tone generator, mono

Introduced as the only form of audio output on the original IBM PC back in August 1981. The PC speaker had the ability to only play one waveform tone at single time making it useless for music and gaming. The notoriety of the speaker’s quality would later earn it the titles, PC squeaker and the PC beeper.

Given what was available on other, cheaper computers at the time one can only assume this offering by IBM was a form of cost cutting. Though, the PC’s target market were business applications so it is understandable why IBM originally choose to ignore audio in its original PC specification.

Unfortunately this limited audio ability would later haunt PC gaming. It would take well over a decade for improved audio replacements to become standard.

Developers did find hacks around the limitations of the PC speaker with various games of the era managing to reproduce multiple toned music, digital sound-fx and even speech. At best these hacks reproduced a 6-bit, single PCM, DAC like channel. Unfortunately various implementation suffered from problems that limited their usage. These hacks were often CPU speed sensitive, whereby a processor could be too fast or slow and would distort or warp the audio output. There were no volume adjustments, just an off/on switch in the computer’s BIOS. The output volume was often too quiet making the audio hard to hear. This was often compounded by the PC’s speaker being placed deep inside the steal casing of the desktop.

A bargain basement Commodore VIC-20 from the same era came with a retail price of US$299.95. In comparison the IBM PC started with a retail price of $1,565 for a base model. Yet the VIC-20 has significantly better audio capabilities than the IBM.

“The VIC chip had three rectangular-wave sound generators. Each had a range of three octaves, and the generators were located on the scale about an octave apart, giving a total range of about five octaves. In addition, there was a white noise generator. There was only one volume control, and the output was in mono.” – Wiki

DOSBox emulates all functionality of the PC speaker including the PCM like DAC hacks; though usually you will need to manually adjust the DOSBox speed (cycles) settings to get it working correctly. Dunzhin: Warrior of Ras Volume I by Computer Applications Unlimited from 1982 is an early example of DAC playback through the PC speaker.

Tandy 1000 / Tandy DAC

3 pulse-width modulation channels plus one white channel, mono
8-bit DAC up to 22050 KHz, mono

The original Tandy 1000 series of computers that first came out in 1984 upgraded the internal PC speaker to three channels plus white noise. Later models also allowed for external volume control and support for headphones. When implemented in software the Tandy 1000 audio is a big improvement over the default PC speaker.

In 1989 Tandy released the 1000 SL series of computers that updated their 3 channel audio chip to incorporate an on board 8-bit, mono DAC/ADC for digital sampling and playback. This was supported by a number of games including a few Sierra titles such as Space Quest III. They experimented with it for a brief period before the Creative Sound Blaster went retail and drew their attention elsewhere.

DOSBox emulates both Tandy audio (3 channel) and Tandy DAC.

I recommend setting the DOSBox.conf tandy=true rather than tandy=auto to force older games to auto-detect the Tandy 3 channel audio. You might also have to set the DOSBox machine=tandy. For Tandy DAC, DOSBox also requires that sbtype= is set to any allowed value other then none.

Covox Speech Thing / Disney Sound Source

8-bit DAC, mono

The Covox Speech Thing was a simple 8-bit DAC/ADC adapter that plugged into a PC’s parallel printer port. Originally released in 1986 it was later revised and marketed under various companies and brands. Including by Disney who in the early 1990’s marketed the Covox for use with their education software.

Note there are a few games out there that support a different device called the Covox Voice Master and the Covox Sound Master. These were internal sound cards rather than printer port adaptors. So unfortunately DOSBox does not support these internal Covox based cards.

DOSBox emulates the Covox printer devices including The Disney Sound Source which offers better audio quality.

AdLib / OPL2 / YM3812

9 channel FM synthesis, mono

Introduced in 1987 the AdLib Music Synthesizer Card was the first add-on music card to gain wide spread support within the PC industry. While it wasn’t the first, nor the most popular, it became the de-facto standard for software developers in the early 1990’s when music and sound card support first became common.

To implement support early games often required an AdLib driver known as a DOS TSR (Terminate and Stay Resident) to be loaded into memory. This requirement was later dropped as many games included and loaded their own audio drivers. The card used a Yamaha YM3812 9 channel FM synthesis chip which is also known as the OPL-2.

MobyGames states that in 1987 there were only 3 games with AdLib support. By 1988 there were 9 games, 53 out of 342 games in 1989 and 138 out of 406 games in 1990, 150 out of 381 games in 1991.

DOSBox emulates AdLib audio. AdLib emulation is set using oplmode=auto setting in the DOSBox.conf to control emulation. opl2 emulates the original AdLib that is also used by the original Sound Blaster. dualopl2 emulates two OPL-2 chips as used by the first generation of Sound Blaster Pro cards. opl3 emulates the AdLib Gold series of cards and was also used by the Sound Blaster 16.

Roland MPU-401 Interface; MT-32 / MT-100 / CM-32L / CM-64 / LAPC-I

32 channel LA synthesis, stereo

DOSBox provides support for the MPU-401 (MIDI Processing Unit) interface created in 1984 by the Japanese audio company Roland to enable customers to connect MIDI-compatible devices to their home computers. Initially this interface support was through standalone cards but partial support was later incorporated into many third-party sound and joystick add-on cards.

The Roland MT-32 Multi-Timbre Sound Module from 1987 was a programmable synthesiser that supported up to 32 notes played at once using a 16-bit DAC at a sample rate of 32000 HZ. To connect to and use on a PC this standalone device required a MPU-401 interface installed on the host machine.

Also from Roland in this year was the MT-100 which for our purposes is the same MT-32 device in a different form factor.

Many DOS games from the period support music playback using Roland’s famed MT-32 sound module, as the audio quality output was better than the competing but cheaper AdLib sound card. Unfortunately the expensive combination of the MT-32 sound module and the required MPU-401 compatible interface card meant support wasn’t as widespread.

The Roland LAPC-I (Linear Arithmetic Personal Computer IBM) from 1989 was a PC card that joined the MPU-401 interface card with a near-compatible MT32 sound module and incorporated both their functionalities into a single, easier to set-up device.

Also in 1989 Roland released the first of a series of CM (Computer Module) sound modules. Some of which improved on but were also mostly compatible with the MT32 module. Models included the CM-32L which was an improved MT-32 with 33 added sound-effect samples. And the CM-64 which was a more expensive model of the CM32L with extra functionality geared towards computer musicians.

Now to complicate things MPU-401 has two modes, ‘intelligent’ and ‘UART’ that is otherwise called dumb mode. Many ‘MPU-401 compatible’ cards and devices only support UART mode. In UART mode the attached MPU-401 component acts as a dumb playback device. While the intelligent mode, the attached device handles part of the audio processing. This more complex mode allows computers with the slowest generation of Intel PC CPU’s (such as the 8086 and 8088) to handle MIDI playback. But intelligent mode had become redundant when support for these CPUs were abandoned in favour of faster chips that could handle the audio processing themselves.

Annoyingly many legacy DOS games of the late 1980s expect the intelligent mode for MT-32 audio playback. To get around this many of these games have post-release software hacks known as patches that enable them to use a MT-32 sound module attached to a computer with a UART only MPU-401 connection.

Fortunately DOSBox can emulate both MPU-401 modes using the mpu401=intelligent or mpu401=uart settings. So you can attach a MT-32 or compatible sound module to your computer to receive authentic music playback but avoid patching the games.

Creative Music System / Game Blaster

Twin 6 channel FM synthesis, stereo

Creative Music System released in 1987 was the first add-on sound card by the Singaporean based company that would later become Creative Labs. The card used two Philips SAA 1099 chips that each supported 6 channels of waveforms in stereo. Price at a similar level to the AdLib the CMS audio was of poorer quality and so it never gained wide industry support.

sounding not unlike twelve simultaneous PC speakers

MobyGames game support: in 1987 there was one game with CMS support, 6 in 1988 and 17 in 1989. By 1990 there were 40 games but this dropped down to 17 titles in 1991 after Creative’s Sound Blaster was popularised.

DOSBox emulates CMS sound. It must be manually set by changing oplmode=cms in DOSBox.conf. This setting by default disables AdLib audio.

Sound Blaster 1 / 2

9 channel FM synthesis, single 8-bit DSP, mono

Sound Blaster 1.0 first appeared in 1989 and was the successor to the not so popular Creative Music System that was by then known as the Game Blaster. The Sound Blaster 1.0 was a kind of hybrid card in that it offered backwards support for its earlier Game Blaster series. It also included the Yamaha YM3813 chip that was used in the more popular AdLib card. In addition Creative also included a digital signal processor allowing the playback of sampled sound at 23 KHz and recording at 12 KHz. Priced in retail at the same level as the AdLib and with the additional value add-ons such as a built in game port. The Sound Blaster out valued and out featured its rival and eventually forced the AdLib company to file for bankruptcy.

MobyGames game support: 4 in 1988, 9 in 1989, 71 in 1990, 115 in 1991.

The Sound Blaster 1.5 released in 1990 did not include the chips that enabled legacy Game Blaster support which was probably done as a cost cutting measure. But these chips could be purchased separately from Creative and attached to the device by the user.

The Sound Blaster 2.0 was released in 1991 and offered improvements to the digital signal processor chip. It upgraded the playback to 44KHz in 8-bits and allowed for auto-DMA which removed an undesirable clicking sound that was audible in earlier cards.

Sound Blaster Pro

Twin 9 channel FM synthesis, twin 8-bit DSP, stereo

Sound Blaster Pro 1.0 for all intent and purposes was the successor to the Sound Blaster series of cards with the introduction stereo. Like the earlier CMS line of cards it used two YM3812 chips to emulate stereo. Though games had to be specially programmed for this to work otherwise they would only playback in mono off a single chip. The DSP chip was upgraded to allow for 44KHz, 8-bit samples in mono or 22KHz samples in stereo.

Sound Blaster Pro 2.0 removed the twin YM3812 chips and replaced them with a single Yamaha YMF262 chip otherwise known as the OPL-3. It allowed for 20 FM synthesis channels played back in stereo.

DOSBox emulates the Sound Blaster 1, 2 and Pro. sbtype= allows you to manually force Sound Blaster emulation. sb1 emulates the original mono Sound Blaster. sb2 emulates revision 2 of the same card. sbpro1 emulates Sound Blaster Pro. sbpro2 emulates revision 2 of the card. sb16 emulates the Sound Blaster 16.

Pro AudioSpectrum (PAS)

Twin 9 channel FM synthesis, 8-bit DSP, stereo

Created by the Californian based Media Vision. The first Pro AudioSpectrum released in 1991 was an 8-bit stereo card that used two YM3812 chips for FM music and had its own custom DSP chip. I am pretty sure the DSP chip was stereo but a lack of Sound Blaster compatibly limited its appeal. It did however include a SCSI CD-ROM interface allowing the connection of a then, new to the market CD-ROM drive. At this time there were significant savings to have had for buyers who purchased a Pro AudioSpectrum for use with a CD-ROM drive instead of a SoundBlaster Pro with a separate SCSI interface card.

There is no AudioSpectum emulation in DOSBox.

Sound Blaster 16

18 channel FM synthesis, 16-bit 44KHz DSP, stereo

Released in the middle of 1992 the 16 series was the next major upgrade to the Sound Blaster range of cards. It finally saw Creative catch up to it’s competitors by offering 16-bit, 44KHz playback while the music playback was upgraded to the now standard Yamaha OPL-3 chip. At retail the card came with the usual Creative price mark-up but it did offer official backward compatibility with the earlier Sound Blaster series.

DOSBox emulates SoundBlaster 16 audio.

Gravis Ultra Sound

14 wave-sampled channels at 16 bit 44KHz DSP or 32 channels at 19Khz, stereo

In 1992 Advanced Gravis a well known Canadian joystick company released the physically large, bright red Gravis Ultra Sound add-on card. Priced slightly higher than the Sound Blaster Pro the Ultra Sound gave owners significant bang for their bucks. Unfortunately this added value was at the expense of Sound Blaster compatibility which left most new owners with a collection of games that had limited or no audio support.

The card itself was a wave-table sound card with 256kbs of RAM built-in. Unlike it’s competitor the Sound Blaster AWE-32, the Gravis did not come with any pre-saved samples and everything had to be loaded through software drivers or by the game itself. As the card did not offer any hardware emulation for the Sound Blaster DSP chip or even then ancient AdLib OPL-2 music chip, all legacy audio had to be emulated using uploaded samples. This process required extra computer memory, CPU resources and often utilised hacks to get many unsupported games to partially work. As such some owners of the Gravis would also install a cheap Sound Blaster clone in their PC for better gaming compatibility.

On the plus side when games did offer support for the Gravis it offered a far greater audio capability than anything else on the home consumer market. It allowed for 14 channels at 44KHz playback or 32 channels at 19.2KHz.

A number of games require the use of Gravis drivers that can be downloaded from here. These cannot be distributed with DOSBox as their copyright is incompatible with the DOSBox GNU open source license. You will need to unzip the drivers to a directory which is usable within the DOSBox shell and then change ultradir= to point to this directory. Other then this drive requirement DOSBox offers complete Gravis Ultra Sound emulation.

Sound Blaster AWE32

30 channel wave synthesis, 16-bit 44KHz DSP, stereo, EAX like effects

In early 1994 Creative released the Sound Blaster AWE-32 which for all intents and purposes was basically a Sound Blaster 16 with a built in synthesizer board and effects chip. These enhancements were useless unless the game directly supported them, which was a rarity. The card came with a 1mbit sample ROM and included 512kbit of RAM for user samples. It used 30 sampled channels plus an additional two channels for the FM OPL-3 synthesizer.

Using software drivers it could also attempt to emulate General MIDI and MT-32 audio playback. The drivers required for this consumed valuable conventional memory and were not able to work with common 32-bit protect mode DOS programs.

A budget version of the card known as the Sound Blaster 32 was released in 1995. It removed the included on-board RAM as well as support for bass, treble and gain adjustments.

There is no DOSBox emulation for the AWE32 series.

General MIDI – GM

16 melodic and 8 percussion voices

Is an enhanced and standardised specification for MIDI (Musical Instrument Digital Interface). It assigns specific instruments to MIDI program messages, so that any General MIDI device receiving program message 18 will always play a ‘rock organ’, while program message 28 will always be a ‘muted rock guitar’, etc.

Codified in 1991 by the MIDI Manufacturers Association and Japan MIDI Standards Committee the GM standard was partly made redundant on release by Roland’s competing and backward compatible GS format.

One of GM’s major problems was the lack of quality requirements on the timbres used. So the instrument representation on a GM device from one manufacturer could be much poorer than on another.

Many DOS games from the 1990’s support General MIDI but their music reproduction varies depending on the GM device used for playback. Most game musicians composed their tracks on Roland Sound Canvas products and so they would be a good bet for accurate playback.

Roland General MIDI only playback products. SC-7 Sound Module from 1992 was unique as it allowed a connection to the PC or Mac using a serial port. RAP10/AT Roland Production Audio Card from 1994 included a stereo 16bit 44.1Khz DSP.

Roland GS – Sound Canvas

16 melodic and 8 percussion voices

Created in 1991 and pushed by Roland the proprietary GS format is a backwards compatible extension to General MIDI. GS products even reached the consumer market first and the format allowed for more varieties of instruments than GM plus it gave Roland flexibility for future enhancements.

The Sound Canvas with its famous SC series of cards and modules was the branding that Roland most used to push consumers to the GS format. To confuse things there were a large number of GS compatible products to target various segments of the market from home consumers to professional musicians. So the few DOS games that support playback on GS devices generally list ‘Sound Canvas’ support and not the specific models.

Select Roland ‘Sound Canvas MIDI Sound Generator’ GS modules. SC-55 from 1991. SC-155 from 1992. SC-55 Mark II from 1993. SC-50 from 1993. SC-88 from 1994.

Select Roland computer modules. CM-300 from 1991 was GS compatible. CM-500 from 1991 was GS and LAPC-I compatible.

Select Roland GS ‘Sound Canvas PC Cards’ SCC-1 from 1991. SCP-55 from 1995.

Yamaha XG

32 simultaneous voices

First released to the public in 1994 the XG format is another proprietary extension to the General MIDI standard. While it offered a greater variety of instruments than either GM or GS it was never directly supported by DOS games. Though the product range’s General MIDI playback performance was different enough for the format to earn its own gamer fan-base.

General MIDI Emulation

These days most computers use software based synthesisers to playback General MIDI tracks. Windows uses the ‘Microsoft GS Wavetable SW Synth’ which uses a version of Roland’s Virtual Sound Canvas and supports the GS format. While on the OSX uses Apple’s ‘QuickTime Music Synthesizer’ which also uses software licensed from Roland.

Windows users can also use the free BASSMIDI freeware driver to apply and use different SoundFonts for its software synthesiser.

DOSBox Supported Devices … which are the best to use?

These charts are a matter of personal opinion and is based on running DOSBox under Windows XP/Vista host system with a Sound Blaster Audigy 2 and a pair of amplified stereo speakers. Of course audio quality will also depend on the software or game operating under DOSBox.

# Music
1 Roland Sound Canvas (physical device)
2 Gravis UltraSound (with correct ROMs)
3 General MIDI (software emulation)
4 Gravis UltraSound
5 Roland MT-32 (physical device)
6 Sound Blaster 16 / Sound Blaster Pro 2 / OPL-3
7 Roland MT-32 (when mapped to a GM driver)
8 Sound Blaster Pro
9 Sound Blaster / AdLib / OPL-2
10 Creative Sound Master / Game Blaster
11 Tandy 1000
12 PC Speaker
# Sound effects and speech
1 Gravis UltraSound
2 Sound Blaster 16
3 Sound Blaster Pro
4 Sound Blaster
5 Disney Sound Source, Covox Speech Thing, Tandy DAC
6 Tandy 1000, Creative Sound Master, Game Blaster, PC speaker
7 AdLib, MT-32

Written by Ben Garrett