I have 3 Bass Guitars, Dean Edge with 2 pickups, Squier Precision with 1 split pickup near the neck and a solid pickup near the bridge, and a SBMM Stingray with one pickup. My question is about the knobs. The SBMM HAS 3 adjustable knobs for volume, tone and ? I don’t know what the 3rd knob is for and which knob does which function, I have the same question about the Dean. It has 2 pickups and 3 knobs that I assume are 2 volume and 1 tone. Which is which though? My Squier has a split pickup and a solid pickup. According to the info from the internet the knob closest to the neck is volume for the neck pickup, the middle knob is volume for the bridge pickup and the last one is tone. Can’t really apply that to the SBMM because it has only one pickup. Sorry for the long post that I should have figured out long ago. Any insight into the SBMM and DEAN Layout would be appreciated.
I am sure you have tried to notice what changes when you turn each of the knobs individually!?! That should give you some indication of their function.
It all goes back to two archetypes - the P-bass and the J-bass.
The P-bass has one pickup, one volume control and one tone control.
The J-bass has two pickups, one volume control for each pickup, and one (common) tone control.
That’s the classic layout for passive basses with either one or two pickups. Then, people started modding and making variations. E.g., many (including myself) don’t like the VVT (volume-volume-tone) setup of the Jazz bass, and instead prefer a VBT setup (one overall volume, one blend or balance tone to select how much the two pickups contribute, and one overall tone control).
But, then you also have active basses, i.e., basses with a pre-amp installed. And depending on type of pre-amp, you have at least two controls apart from an overall volume control (lower frequency boost/cut, and higher frequency boost/cut), but most often you find a so-called three-band preamp, with three controls besides the volume (los, mids, his cut and boost). Note, that here you also might have a balance/blend control if you have more than one pickup.
Maybe this helps already a bit!?
Sbmm 3 knobs is volume bass and treble. It’s their classic 2 band eq layout. So when you get the 4 knobs it would be volume /treble /mid/ bass.
On your Dean it depends. It could be vol/vol tone or vol/blend/tone. It’s almost the same but not quite. Hope this helps.
I have tried turning each knob to see what change happened. Some of them there is almost no noticeable change.
Yes, some of these changes can be “hard” to hear, if you are not used to listening to those things. And some changes are more subtle than others.
Try to pluck a note and let it ring while you turn the knobs; also, try to turn them to their extreme positions back and forth fast (while the note is ringing).
(If all of this is obvious to you, my apologies. Just trying to come up with stuff that might help 
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Thanks for the input, I have tried that, my wife is watching football so I am using headphones so I don’t disturb her. Have to try all those test again during halftime. I appreciate all the help, Thank you.
On my very first bass (a cheap, second-hand Harley Benton), I couldn’t hear any difference when I turned the tone knob all the way up or down. At first I thought it was defective, but when I put on a set of new strings, the difference was night and day.
Fastest way to check the tone is to pop the g strings. If the tone is all the way open you’d get this crisp popping tone if it’s not then it’s either not a tone knob or it turns the other way, lol.
I wire some of my basses with a 4 band Audere preamp. I have a master volume, and balance, treble, bass hi-mid, and lo-mid controls. That is an active preamp. I have some passive basses wired with a toggle, and a volume and a tone for each pickup.