for the visual thinkers out there, I'd like to discuss something. visually.
my primary job is as a sound recordist/mixer, and I do this sort of analysis from time to time; "what is needed, what is not, and how does this clean up nicely in a mix with minimal ongoing effort."
I also play professional music. a lot.
heres my double bass E string, plucked + ringing average for 4 seconds.
direct from bass and into ua apollo with no filters or effects.
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first screenshot is an E played on double bass (red) vs 63 P (green). christmas colors.
from the bottom (left) there is a gentle shoulder rising to the first peak at 42hz, then there is a trough at about 50hz (49 for db and 51 for electrric), then there is another peak at 83hz. the next trough is at 97hz, and above that the peak is at 125hz.
2nd screenshot:
yellow = flat
purple = 6db/oct@90hz
blue = 24db/oct@60hz
green = brickwall
@60hz
this is a visual representation of what the filters look like.
3rd screenshot:
red = clean signal
yelllow = 6db/oct@90hz
blue = 24db/oct@60hz
dark green = brickwall@50hz
lighter green = brickwall@53hz
purple = brickwall@60hz
this is what the signal from my bass looks like without (red) and with these three filters applied (different filter colors, sorry).
the brickwall filter at 53hz takes the 50hz trough clean out, and is the cleanest place for a HPF for this recording.
human speech can be cut at 80hz (hpf, usually applied in film/tv editing) without notice, which could be why a typical soundboard high pass is about 75hz. but that is too high for bass guitar/double bass.
sound reinforcement systems (especially when subs are involved), are criticized for reproducing delicate double bass subharmonic frequencies unnaturally and they often create feedback (or simply sound unnatural) and not every engineer is able to do something useful for this.
the kick drum should push the subs harder than the bass.
in the studio I often use a schoeps CMC with a CUT60 (inline HPF, 24db/oct@60hz) which significantly reduces that low 42hz peak, and is very effective for "rumble" (everything even lower which doesn't belong there anyways), and I think of this as a minimum for the signal chain (I usually edit each take with a brickwall hpf, set at 60hz).
this translates to a good starting point for which a track is able to be put directly into a mix, and blends well with a kick drum without having to do something more tone-wise, just to blend to taste with volume.
as a bassist and sound nerd, I've found that 60hz is a real nice common cleanup frequency, and it has worked well on many recordings over the years, not to mention reducing the AC mains problem in north america....
the point of this is that 6db@90hz is a subjective tone shaper, whereas a hard HPF at about 60hz is a tool for clarity.
YMMV