I recently saw a video where bassist Adam Neely did a harmonic slide on a fretless bass, and he said it was also possible to do on a fretted bass. I have attempted to do them but I cannot figure it out. Does anybody know how to do these slides?
A couple of things. When sliding harmonics on a fretless, it's easiest to use natural harmonics. after a harmonic is played, the string needs to be pressed onto the fingerboard, but then the slide must be from that harmonic node to another one. It won't work just going anywhere at random. Remember that plucking the string as close to the bridge as possible makes it easier to produce good artificial harmonics.
A more effective and useful way is to play an artificial harmonic - just like on guitar. I touch a node with thumb (r.h.) and pluck with a finger from the same hand. No need to hit, and it's not a pinched harmonic either. Most effective here is to fret on any fret, and put the r.h. thumb exactly 12 frets higher. Now the string is split in half, and the 1st harmonic is played. By sliding the fretting finger up or down, anywhere can be your target note. The node seems to follow without being told. There is probably some scientific reasoning behind it - I call it magic. All this on fretless. 12th fret above, as said, is most effective, but it also works 7 and 5 frets above (equivalent to 19 and 21) too.
On fretted, it works to some degree. But, rather like hammering on or sliding, the basic note is heard too. And, sadly, it's not possible to pluck close to the bridge - think about it !
The strongest harmonic is the octave, twelve frets up from whatever note you're fretting. The seven-frets and five-frets might work, but go for the twelve. The trick is to pick and hit the harmonic node with the same hand, because your fretting hand is fretting. Because physics, the note will sound stronger sliding higher than going lower, so do that.
I saw a roots rock band do that with a slide to finish a bluesy, rocking cover of "Walking After Midnight" 30 years ago, and so I know it as a slide thing, starting on an open string. In the Neely case, basses have strings that have a lot of mass, which will keep vibrating. With frets, it will likely sound more stairsteppy than on a fretless.
The accurate picking while hitting the node will be the thing that makes this work, and this is the thing that makes this easier with a fretted bass, unless your fretless has fret markers. Consistently hitting the harmonics on different strings and frets should be your first thing — that's one of the cool things that Jaco brought in — and once you have that in your hands, moving the note is the easy part.