The Sounds of MIDI Synthesis Engines
MIDI, standing for Musical Instrument Digital Interface, was initially was a connection standard used to connect musical instruments together to exchange data. However, it also evolved into a file format which allows musical notes and data to be stored into files on a computer. MIDI files are small, and can be thought of as sheet music to be interpreted and played by a computer. Unfortunately, many people in the early days lost interest in the format, as many home users considered it inferior, electronic and robotic. The cause of this wasn't because of any inadequacies in MIDI itself, but in the Synthesis Engines they were using. That being said, MIDI Synthesis engines have improved over time, employing wavetable and sample based techniques to overcome the perceived artificial sound quality. Unfortunately, one of the drawbacks of the MIDI system was that the same MIDI file played across different equipment might sound completely different depending on the device. Here are some samples of this MIDI file rendered by different soundcards using different synthesis technology - all of which were recorded from my collection of gear. Most of them are recorded from the last cards of the generation and so they have better quality than would be expected of the cards commonly in use in those days.
Soundblaster FM MIDI Engine (from an AWE64 Gold Edition ISA card)
The Soundblaster FM MIDI engine was considered to be the standard for a long time - with many computers in the DOS era featuring Soundblaster cards. They featured the Yamaha OPL2 or OPL3 Frequency Modulation Synthesis chip which produces a variety of General MIDI sounds from several frequency generators and mixers. While the quality was very synthetic, it was very characteristic of the era - it reminds me of the good old Gameboy.
Avance Logic FM MIDI Engine (from an ALS4000 PCI card)
The Avance Logic card was a relatively popular low-end alternative to the Soundblaster of the day. It was much cheaper, but the quality was rather nasty. The card contains a hardware synthesis engine which uses the FM technique which is compatible with the Yamaha OPL3 but, while being compatible, it doesn't sound identical.
ESS FM MIDI Engine (from an ESS Onboard Soundcard)
This card was commonly bought as a cheap alternative to the Soundblaster, and featured on many many cheap all-in-one motherboards of the day. It featured a hardware FM engine as well, however, it seems to be quite buggy and incomplete. When listening to this file, you'll realize that many sounds start to go missing, get clipped or get turned into some garbage - this is likely because of some incomplete or buggy implementation of the MIDI standard and also because they chose to be cheap and feature very few voices. A voice is essentially the ability to make a sound - the more voices a card supports, the more sounds the card can play simultaneously. If a card is unable to make enough sounds to render a MIDI file, you will end up with something that sounds like the above.
Microsoft GS Wavetable Synthesis (available on all cards)
Many soundcards, upon the advent of Windows 2000, had decided to no longer include FM synthesis in hardware. The reasons were twofold - FM synthesis had poor quality, and also to fabricate the FM synthesis on chip costed money. So many soundcard chipset manufacturers just simply stopped including any hardware MIDI support, and instead relied on software. Some provided their own Wavetable in software, then criticised for using too much CPU and being poor performing, while others didn't bother doing it at all - instead relying on the Microsoft GS Wavetable Synthesis engine which was first packaged with Windows 2000. Its quality could hardly be described as a quantum leap over FM synthesis, but on the upside, it was "free". Most users nowadays using most soundcards are using this as the default synthesis engine under Windows. Unfortunately, this option is only in software, and therefore was not available to DOS programs directly.
Soundblaster AWE32 and AWE64 Wavetable MIDI Engine (from an AWE64 Gold Edition ISA Card)
Creative, instead of using software synthesis, decided to go with hardware wavetable MIDI synthesis instead. This overcomes the hardware limitations with CPU and RAM utilization and provides low latency, high quality MIDI synthesis. Unfortunately this was only true of the AWE32, the AWE64 instead had to rely on half software, half hardware synthesis to achieve the full number of available voices advertised. However, that being said, this was still one of the best MIDI engines in my memory. It had memory for downloadable Soundfonts which allow for the wavetable to be custom updated. It was still DOS compatible as well.
Yamaha XG Synthesis Engine (available on all soundcards, but no longer)
Yamaha's XG engines, since discontinued, was a software package available for Windows which allows for any soundcard to produce high quality sounding MIDI audio. Unfortunately, this product has been discontinued, but it was certainly efficient enough to be run on a fairly low spec Pentium 1 machine in realtime, however, using almost all the CPU. It promised CD quality MIDI audio and to my ears, it really delivers. It also offered several patch bank extensions to Roland's GM system which allowed for other special effects, however, files written for XG don't usually sound all that good when rendered on an engine which supports only GM. This engine can still be found online unofficially, however, its use is unsupported and it seems to have issues with working on dual-core machines.
Soundblaster 5.1 Synthesis (from a Soundblaster 5.1 PCI Card)
Creative eventually moved to pure software-only synthesis, which went by many different names, but was marginally better than that offered by Microsoft. I don't really have much to say about this one because it is pretty card specific, only allowed to be used with certain Creative cards.
Soundblaster X-Fi Synthesis (from a Soundblaster X-Fi XtremeMusic PCI Card)
The software synthesis did evolve quite a bit to the latest iteration of X-Fi cards. That being said, it is still a Creative proprietary specialty which can only be used with their cards.
Natural Instruments Bandstand (available on all cards)
This piece of software comes on a DVD and features real samples of instruments and uses software synthesis techniques to blend them together into something good. As memory and processing time has gotten cheaper nowadays, it is now affordable and acceptable to use a large library of real samples to provide the most realistic experiences. Unfortunately, latency is still a problem due to the amount of data being shuffled and the amount of buffer time required to make sure the sound is continuous and without interruption.