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.5.14
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.5.15 A disadavantage 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 this cards have. Modern cards have normally much more onboard ROM/RAM, but in our opinion even 32MB are far to 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 an easily change a single instrument, if you don't like the default sound and that only intruments are loaded (and therefore memory needed) which are actually used by the file.
At the moment two different formats for those midi patches are supported. Both were introduced with the Gravis Ultrasound Cards. The older one using files with the extension .pat and a file describing the patch set default.cfg. With the GUS PnP a new midi patch format was introduced using .ff files and a configuration file called ultrasnd.ini.
To use those patch sets simply copy all files into one directory and use the ultradir option of the general section to point to the appropriate directory. OPENCP will then process this file if a .mid file is selected and load the defined patch sets.
If you are not owning a Gravis Card you will have to get a patch set from our homepage5.16 and install it in any directory. Note that most patch sets are not public domain or freeware, so check out if you are allowed to copy and use those samples.