Acoustics! Did you know that the wavelength of the fundamental ‘E’ on your bass (which sounds an octave lower than written) is an astounding 27 feet in length from crest to crest? This helps explain why the brain perceives the higher frequencies sooner than the lower ones. The great Ray Brown was keenly aware of this fact. Though Ray was always the first in the band to get to the down beat, he certainly never pushed the tempo (think about it). No wonder Ray Brown remains the all time master of groove. Note that a great ‘swing’ groove requires each subdivision of a beat be divided into 3 subsections: 1) bass slightly on ‘top’ of the beat, 2) drums ‘on’ the beat, 3) melody slightly ‘behind’ the beat. This is why swing ‘swings’! These rules carry over to the critical condition of ANY groove: 1) bass never behind the beat, 2) drums never EVER behind the beat, 3) melody never ahead of the beat. Note: some drummers think it’s cool to ‘Lay back’. WRONG! Horns and vocals lay back all day- the further the better. Never the rhythm section! Horns and vocals lay back AGAINST the rhythm section. See Ed Friedland’s, Febuary 18, 2014 article- ‘Tech Bench: Sound Good Live’ in Bass Player.