Rename README.OPL to README.Music and extend.

Chocolate Doom now has a bewildering array of different options for
music playback and it's worth documenting them properly. Extend the
existing README.OPL file to describe the other options that are
available, and rename it to README.Music as it's no longer just about
OPL playback.

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+
+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 "Native MIDI" 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:
+
+  http://www.doomworld.com/idgames/index.php?file=sounds/eawpats.zip
+
+Having installed a sound font, select "Native MIDI" in the sound
+configuration dialog in the setup tool, and use the "Timidity
+configuration file" 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 '90s,
+notable for having wavetable synthesis that provided MIDI playback
+that was superior to most other cards of the era. Chocolate Doom
+includes a "pseudo-GUS emulation" 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:
+
+  http://www.doomworld.com/idgames/index.php?file=music/dgguspat.zip
+
+Having downloaded the patches, select "GUS (emulated)" in the sound
+configuration dialog in the setup tool, and use the "GUS patch path"
+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 '90s 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 "OPL (Adlib/SB)".
+
+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, here's 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 don't have slots for ISA cards though, so you
+must be running a pretty old machine.
+
+If you have a PCI sound card, you probably don't have an OPL chip.
+However, there are some exceptions to this. The following cards are
+known to include "legacy" 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.
+
+If your machine is not a PC, you don't have an OPL chip, and you will
+have to use the software OPL.
+
+=== Operating System support ===
+
+If you're 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 you're 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 you're 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 "ioperm.sys" 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'.
+
+=== 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 hadware 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 isn't
+listed above, you can set a hook to invoke an external command for
+MIDI playback using the 'snd_musiccmd' configuration file option. For
+example, set:
+
+  snd_musiccmd    "aplaymidi -p 128:0"
+
+in your chocolate-doom.cfg file.
+
+# vim: set tw=70:
+