One of the things that isn't immediately obvious when listening to electronica, is the difference between a bass synth and other synths. Initially one might think that a bass synth might be an analog of the bass guitar, and good at producing bass tones, however bass synths can actually be used for leads and have no frequency range limitations. So what makes a bass synth different from any other synth, well they tend to have all kinds of LFO's and effects and be mono phonic. So why not just take a bass synth and make them polyphonic, well the circutry gets a little complicated, and besides that they would be muddy with all of the effects anyway. So now you can identify bass synths in the wild, small keyboards lots of knobs and buttons, vs a full keyboard built for chords not too many knobs or effects. But what distinguishes a drum synth? I'm afraid I don't have a perfect answer for this. There are a number of typical features for example storing samples, and input devices designed for fast repeated hits, though it seems drum input devices tend to be also support multiple simultaneous notes. The distinction doesn't seem as clear cut as the polyphonic vs monophonic.