This has of course some disadvantages. To hear a MIDI file you need to have some information how to play the used instruments. Back in the old days the OPL2 sound chip which was present on the SoundBlaster cards was used to play the midi instruments. Most people find the sound capabilites of the OPL series rather limited and midi files were no big deal back then.
Things changed when so called wavetable cards became popular. Those card have sample data stored onboard in a ROM plus a hardware mixer capable of mixing several midi channels. The MPU-401 interface from Roland is the de facto standard for accessing those cards, but this feature is not supported by OPENCP yet.4.15 A disadvantage is that those wavetable cards only have a very limited memory for sample data typically 4MB. If you imagine 127 instruments and 64 drums fitting into just 4MB you can guess what sound quality these cards have. Modern cards have normally much more onboard ROM/RAM, but in our opinion even 32MB are far too less for a good sound quality.
OPENCP goes a different way. Instead of using the onboard ROM samples, the samples needed for a specific .MID file are loaded on demand from the harddisk into main memory and then processed by either the hardware mixer (if you have such a card and the samples fit into its memory) or by the software mixers. This has the advantage that you can easily change a single instrument, if you don't like the default sound.
The instruments are stored in so called GUS-patches, a file format introduced by Gravis with their UltraSound cards. At first you have to get a complete patch set. If you own a GUS classic or GUS max you will probably have those files already on your harddisk. All instruments are stored in files ending with .PAT.
You can use the original GUS patches (available on our homepage), look for the EAW patches on the net or try the freepats.
If you unpack any of those archives to a folder on your harddrive, you have to adjust the path in the cp.ini file. The configuratoin directive
ultradir=c:\gus\midi ; path to ULTRASND.INI
should be set to the folder where you extracted the patch files. Please check that a file called ultrasnd.ini is located in this folder, as OPENCP needs this file, to load the patch files.