Doom has a memorable and atmospheric soundtrack. Like many games of the era, it is MIDI-based. Chocolate Doom includes a number of different options for music playback, detailed below. # Native MIDI playback Most modern operating systems have some kind of built-in support for MIDI playback; some have very good quality MIDI playback (Mac OS X for example). To use this, choose âNative MIDIâ in the sound configuration dialog in the setup tool. # Timidity Timidity is a software-based MIDI synthesizer, and a version of it is included in the SDL_mixer library used by Chocolate Doom. To use Timidity for MIDI playback, first download a sound font. An example of a good quality sound font is the eawpats font, which can be downloaded from the idgames archive as sounds/eawpats.zip: https://www.doomworld.com/idgames/sounds/eawpats Having installed a sound font, select âNative MIDIâ in the sound configuration dialog in the setup tool, and use the âTimidity configuration fileâ widget below to enter the path to the Timidity configuration file (normally named timidity.cfg). # Gravis Ultrasound (GUS) The Gravis Ultrasound (GUS) was a PC sound card popular in the â90s, notable for having wavetable synthesis that provided MIDI playback that was superior to most other cards of the era. Chocolate Doom includes a âpseudo-GUS emulationâ feature that simulates the GUS (using Timidity, under the hood). To use this feature you need a copy of the GUS patch files that were distributed with the original GUS patches. If you have Doom 3: BFG Edition, these patches are included with its version of classic Doom, and are automatically detected. Otherwise, they can be downloaded from the idgames archive as music/dgguspat.zip: https://www.doomworld.com/idgames/music/dgguspat Having downloaded the patches, select âGUS (emulated)â in the sound configuration dialog in the setup tool, and use the âGUS patch pathâ widget to enter the path to the directory containing the patch files. By default a GUS card with 1024KB is simulated; to simulate a 256KB, 512KB or 768KB card instead, change the gus_ram_kb option in chocolate-doom.cfg. # OPL (Soundblaster / Adlib) Most people playing Doom in the â90s had Soundblaster-compatible sound cards, which used the Yamaha OPL series of chips for FM-based MIDI synthesis. Chocolate Doom includes the ability to emulate these chips for a retro experience. OPL emulation is the default MIDI playback, but can be selected in the setup tool as âOPL (Adlib/SB)â. Most modern computers do not include an OPL chip any more, as CPUs are fast enough to do decent software MIDI synthesis. However, no software emulator sounds exactly like a real (hardware) OPL chip, and a few cards do have real hardware OPL. If you have such a card, hereâs how to configure Chocolate Doom to use it. ## Sound cards with OPL chips If you have an ISA sound card, it almost certainly includes an OPL chip. Modern computers donât have slots for ISA cards though, so you must be running a pretty old machine. If you have a PCI sound card, you probably donât have an OPL chip. However, there are some exceptions to this. The following cards are known to include âlegacyâ OPL support: * C-Media CMI8738 (*) * Forte Media FM801 * Cards based on the Yamaha YMF724 (*) Other cards that apparently have OPL support but have not been tested: * S3 SonicVibes * AZTech PCI 168 (AZT 3328 chipset) * ESS Solo-1 sound cards (ES1938, ES1946, ES1969 chipset) * Conexant Riptide Audio/Modem combo cards * Cards based on the Crystal Semiconductors CS4281 * Cards based on the Avance Logic ALS300 * Cards based on the Avance Logic ALS4000 If you desperately want hardware OPL music, you may be able to find one of these cards for sale cheap on eBay. For the cards listed above with (\*) next to them, OPL support is disabled by default and must be explictly enabled in software. See sections below for operating system-specific instructions on how you may be able to do this. If your machine is not a PC, you donât have an OPL chip, and you will have to use the software OPL. ## Operating System support If youâre certain that you have a sound card with hardware OPL, you may need to take extra steps to configure your operating system to allow access to it. To do hardware OPL, Chocolate Doom must access the chip directly, which is usually not possible in modern operating systems unless you are running as the superuser (root/Administrator). ### Windows 9x If youâre running Windows 95, 98 or Me, there is no need to configure anything. Windows allows direct access to the OPL chip. You can confirm that hardware OPL is working by checking for this message in stdout.txt: OPL_Init: Using driver 'Win32'. ### Windows NT (including 2000, XP and later) If youâre running an NT-based system, it is not possible to directly access the OPL chip, even when running as Administrator. Fortunately, it is possible to use the âioperm.sysâ driver developed for Cygwin: http://openwince.sourceforge.net/ioperm/ It is not necessary to have Cygwin installed to use this. Copy the ioperm.sys file into the same directory as the Chocolate Doom executable and it should be automatically loaded. You can confirm that hardware OPL is working by checking for this message in stdout.txt: OPL_Init: Using driver 'Win32'. If you have a C-Media CMI8738, you may need to enable the `FM_EN` flag in Windows Device Manager to access hardware OPL output. See [this](http://www.vogons.org/viewtopic.php?f=46&t=36445) thread on vogons.org for some more information. ### Linux If you are using a system based on the Linux kernel, you can access the OPL chip directly, but you must be running as root. You can confirm that hardware OPL is working, by checking for this message on startup: OPL_Init: Using driver 'Linux'. If you are using one of the PCI cards in the list above with a (*) next to it, you may need to manually enable FM legacy support. Add the following to your /etc/modprobe.conf file to do this: options snd-ymfpci fm_port=0x388 options snd-cmipci fm_port=0x388 ### OpenBSD/NetBSD You must be running as root to access the hardware OPL directly. You can confirm that hardware OPL is working by checking for this message on startup: OPL_Init: Using driver 'OpenBSD'. There is no native OPL backend for FreeBSD yet. Sorry! # Other options If you have some other favorite MIDI playback option that isnât listed above, you can set a hook to invoke an external command for MIDI playback using the âsnd_musiccmdâ configuration file option. For example, set: snd_musiccmd "aplaymidi -p 128:0" in your chocolate-doom.cfg file.