I haven't heard the piece, however it may be helpful to identify its fundamental pitch if you have any tool capable of doing (e.g. Using the free REW software if you have a microphone capable of getting down there): 5-string basses (relatively rare back in the 1990s) typically go down to about 31Hz, though of course detuning could drop a few Hz lower. Pipe organs can go down to 16Hz, though you wouldn't really hear that fundamental even live, rather you feel it and hear the harmonics. Synthesizers are unlimited.
As Bart said, the sound could be from a conventional instrument processed (usually a sample subjected to various compression, filtering and pitch modifying), or a synthesised waveform, both of which very likely to have been produced in an instrument like the Korg Trinity, which has a huge range of such sounds built in and can even be used to create completely new sounds beyond the built-in ones ( I know because I have a Trinity). Another instrument that can produce very low bass is the bass pedal synthesiser, commonly used by, for example prog rock bands, especially to provide sustained low and very low notes underpinning parts of the music.
Sometimes the low synthesiser based notes have relatively few higher harmonics, and can be inaudible through speakers that don't extend down to 30Hz or lower, or where there are wider harmonics to be heard they won't give the same sense of feeling and so their is lost.
Unless everything else at the bass end is compressed it is probably less likely to be the result of excessive compression during the recording process, as opposed to a deliberate choice of sound at the time of playing.