Hello! That bass sound does not sound particularly complicated, and you should be able to reproduce it fairly easily.
The first thing that I noticed was that the sound is heavily low-pass filtered. I only really hear bass and mids, so the waveform is hard to say. It doesn’t sound “video-gamey,” but it’s still a rich sound, so I would expect that it’s a sawtooth wave, and likely multiple oscillators, set either to sawtooths as well or to other waveforms like sine.
About halfway through the song, the filter is slowly opened a little, and we hear clearly that the filter is also being controlled by an ADSR. That is what causes the filter to swell in and out of each note, while the peak is set by the filter position (initially fairly low, opened as the song continued). There’s also a lot of resonance as the filter opened a little, which was added progressively through the middle part of the song.
Since the filter’s swelling is so clearly audible, it is likely a different ADSR was used to control amplitude, namely one with a faster attack and slower decay than the one controlling the filter.
It also seems like the filter opens just a tiny bit more as each note sustains, which makes me wonder if an LFO was used for that. Set to a sawtooth and reset by each note trigger, an LFO would produce that subtle swelling of the filter during the Sustain, as contrasted with the clear swelling during the Attack and Decay sections.
In summary:
- At least one sawtooth oscillator, and probably multiple.
- ADSR with slightly fast but noticeable attack and decay.
- LFO set to a slow sawtooth, and reset each time a note is played.
- ADSR and LFO mapped to the filter’s cutoff, LFO only subtly.
- Amplitude ADSR set faster than filter one, such that the swell of the filter is fully audible.
- Filter cutoff and resonance adjusted live or by DAW programmed automation (since The Eraser is Thom’s “laptop album,” he may even have used a softsynth).