Back in 1987, Roland realized that people wanted a larger variety of sounds than the mere analogs of the years before, but due to tight budget and technological limits could only afford a small amount of sample ROM. This transformed into what they call "Linear Arithmetic" synthesis, in which the typical patch would combine PCM samples (usually short attack snippets of an instrument) with what is arguably the first virtual analog engine. Add built-in chorus and reverb (with the ability to have two different chorus effects to a patch), and you have the bulk of the Roland D-50 synthesizer!
From my personal viewpoint, it's amazing how much effort went into many of the patches. This was thanks partially to the fact that, while traditional synthesizers have four stages of an envelope (the first and last being constant), the D-50 and D-550 have five stages, all of which are completely customizable in level and time. This feature is made especially clear through the famous patch "DigitalNativeDance", a patch almost impossible to accurately recreate with traditional ADSR envelopes.
While drum samples are not included (again, sample size limits of the time), what is included is very impressive. Four samples or synth waveforms can be used in a patch. The PCM samples have three different kinds: the aforementioned attack partials, some wavetable-esque loops (the most complex loops are all unusual synth sounds titled "Spect"), and, finally, some basic sequences of samples recorded in a loop. The synth section has the traditional sawtooth and square/pulse waveforms, but can also have a ring modulator applied to it.
If you're feeling too lazy to program yourself, thankfully, there are several SysEx patches for the D-50 and D-550 online, including dumps from all four expansion cards.
Course, the D-550 has the drawback of its LCD screen and lack of easy editability. I had purchased this unit with a very dim backlight, and evidently, I am not the only user with this problem. Thank God for MIDIQuest.
Overall, while difficult to edit without a MIDI librarian, the sounds you can generate from this device will often be worth it, especially if you're into the sound of the late '80s, whether it be synthpop or new age (whose most famous musician, Enya, was also a D-50 user).
I will try to find the time to remake the video, and for the sake of everyone who may be interested in acquiring one, I hope to play short pieces with ALL of the patches in this remake.