Could someone explain slapping?

Question

I have tried to mimic the slap/thump sound.

It feels like I don't understand what slap is, even after spending almost an hour watching tutorials. Is any of the below on the right track?

I tried plucking the string upward and letting it loose, sounded kind of similar since it was more percussive, and I could do it pretty fast since it was like a normal pluck with the end of the thumb just in another direction. But not sure if this was slapping, maybe this was popping or bartok pizz ? (I haven't experimented with the other directions yet)

I tried bouncing on/striking it from above, kind of nice sound for open strings but no sound for stopped strings for some reason. My bass is fretless if that matters? Perhaps it requires a "sharp" left hand?

I tried striking through it with the left part of the bony part in the middle of thumb as a pick but I barely got any sound and it hurt so felt like the wrong thing?

I tried striking through it with the harder part of the end of the thumb (left side of nail), perhaps a little bit less soft sound than usual.

I tried plucking "from below" with the center/middle of the nail on the thumb, kind of similar sound.

Answer 1

Fretless and fretted basses are to a degree rather different animals.There are things one can do on one that aren't so effective on the other.

So it is with slapping and popping. The lack of fretwires mean that the strings get popped onto the wood on a fretless. That means the sound will be less 'harsh' than popping onto metal on a fretted.

The same applies to slapping, where the boney part of the thumb is 'flicked' onto the strings. They then hit wood (fretless), or metal (fretted). Again, the sound will be different, just like a xylophone sounds different from a glockenspiel - for the same basic reasons. Or, put another way, the difference between plucking normally with flesh as opposed to a pick.

So, you're not going to achieve such a resplendent slap on a fretless, although slapping (and popping) are both possible. It's just that the resulting effect will be different.

EDIT: the slap sound is always going to be sharper when using roundwound strings - which are sometimes used on fretless basses. Lots of slapping (and popping) may well leave indents in your fretboard - not a good thing. Using flats will negate that, but at the same time make the sound duller.

Often wondered if it's feasible to have one fretwire near the end of the fretboard (maybe fret 24?) so slap 'n' pop is more effective.

Answer 2

I tried plucking the string upward and letting it loose

This is not done in standard slap technique – not with the thumb, that is. It's what normally the index finger does on the high strings, called pop, while the thumb slaps the low strings. It's of course possible to do that also with the thumb on the low strings, but it won't give you access to the typical fast, drum-pattern-like slap licks.

However, it's worth noting that the classic double bass slap technique, best known from rockabilly music, is mostly based on plucking up the low strings and smashing them onto the fingerboard, which is of course fretless. That way it is possible to get quite a lot of percussive treble, but this comes more from the fingerboard itself and isn't captured well by magnetic pickups.
Again, this technique does not use the thumb, but rather the side of the index finger, to pluck up the strings. And that's than paired with purely-percussive beats of the flat hand onto the strings+fretboard.

I tried bouncing on/striking it from above

That is indeed a usable technique on electric bass, but as you've noticed it's hard to produce much of a tone at all this way on fretless. It pretty much requires frets and fresh roundwound strings, and also enough practice in bouncing back the thumb real fast so it won't damp the string right away.

I tried striking through it with the left part of the bony part in the middle of thumb

That would perhaps be the “official” way to do slapping, and it can work even on fretless, but it's not easy. It requires slamming your finger into the string quite violently so it fits the fretboard. Yes, this will hurt for a while while you're learning. And again it's much easier to get the sound on a fretted bass, especially with low action. Also, ensure you're hitting the string quite close to the fretboard, but not on/over the fretboard itself.

Generally, uncoated roundwound strings give by far the slappiest results, but I also wouldn't recommend that on a fretless (with wooden fingerboard) because it's a recipe for wearing out the fingerboard very quickly. With flatwound, polished or plastic-coated strings however, it's hard to get any sort of slap at all out of the bass.

Finally, of course you won't get a good slap sound with any technique on any bass of the treble doesn't come through. Active basses make it easiest to bring out the percussion, but a passive one with tone pot turned up should be ok to. An amp with a HF horn brings out the slap loudest (in fact, perhaps too loud), but one that only has multiple 10" speakers should work good as well. Single 12" or 15" speaker, not so much.