I think the keyboard player is conferring he's not happy. I don't necessarily think what he is saying is an accurate description of the problem or solution.
Attack is in the higher mids. A strong attack can improve our perception of clarity but IMHO it doesn't carry a lot of information regarding pitch.
From what I have heard, a lot of recordings with Baby Basses have a pretty strong attack, but they don't typically have a super centered tone. I think this is an intrinsic quality of the instrument that sounds very cool while also being potentially problematic.
Frequency Slotting: This is the term we use when someone is managing the mix by cutting a certain frequency range on one instrument and boosting the same frequency range on another instruments.
Masking: When two sound sources produce the same frequency, you only hear the sound source that is louder. The quieter sound sourced is "masked."
I believe pitch perception for bass is largely encoded in the mids. There is a lot of competition in this frequency range, which can mask the bass's pitch. To overcome the masking, it's import to hear more of the direct sound coming from your amp in relation to the indirect sound bouncing around the room. Bass cabs tend to be somewhat directional in the mids. You could aim your cab at the keyboard player, which I don't recommend because it's important for you to hear you own instrument clearly. Alternatively, the keyboard player can take care to set up closer to the area where you amp shoots the mids. Some degree of compromise may be required, so that both of you get what you need.
The benefit of scooping out mids often relates to indirect sound. As I mentioned there is a lot of competition for space in the mids, and especially the lower mids. Low mids are less directional than higher frequencies and they tend to bounce around longer and build up into a muddy mess. The indirect sound of your bass can masks the direct sound of your bass.
One reason for cutting is to reduce how much energy is put into the room at problem frequencies. It can be beneficial to cut frequencies where there is a lot of build up, or ringing. However, if the bass cuts too many of the frequencies that carry pitch info, it's not going to resolve your problem. The ideal solution would be for other instruments to produce less energy in the range the bass needs to occupy.
Guitar, piano, drums, bari/tenor saxophones, trombones, and vocals all compete with bass for space in the low mids. As an audio tech I tend to be pretty aggressive with high pass filters on the mixing console. It can also help if the guitar and keyboard player dial back their lows a bit. The keyboard player should also be careful to avoid voicing chords too low or hammering out competing bass lines with his left hand. This seems to be surprising hard for many keyboardists
.
Unfortunately many players tend to be protective of their own sound and they may be unwilling to consider that they are encroaching into or possibly hogging somebody else's sonic space. If someone is unwilling to work out a reasonable compromise, ultimately the best solution may be for them to accept reality and lower their expectations. Unfortunately that won't make them happy. So you have to consider the big picture; I.E. how much compromise can you take on before it's no longer worth it for you to play in the group. IMHO while I do think you should be a team player and try to give other players what the want, you also need to establish and maintain reasonable boundaries.
Good luck!
