Re: SD Custom Shop....how long
Why? When an electric guitar is played through a cabinet/speakers, those frequencies generally aren't reproduced audibly/accurately. You can "cut" it at 20kHz if you want (or the 17kHz+ range that Drex suggested), but the pros know better.
That "tail" we are talking about lies between, say, 5 and low teens kilohertz. It's just a name I made up for the spectral content of a guitar track that lies above the speakers' cutoff point. It's faint, but it's there. It's not the meat and potatoes of a guitar track, it is either "contamination" or "spice", depending on how you look at it.
Choosing a cutoff point at 17 or 20 kHz doesn't affect anything, as you've correctly stated. That's because a guitar track typically contains nothing there, so it's an obvious case of muting silence.
However, as you move the lowpass cutoff point to a lower frequency, you are going to attenuate the "tail" somewhat. A number of guys like to trim it slightly, others leave it alone. In most cases it boils down to making the aesthetic choice between going for a modern, highly-processed, polished, leave-no-stone-unturned mix or a vintage, raw, unaffected, undisturbed and naturalistic one.
Take a look at the Vintage 30's frequency response plot I've borrowed from Celestion:
The 2-3k range has two peaks resembling cat's ears. These are the upper mids where the guitar cuts through the band mix.
The small peak at 4k gives it presence or fizz. It's a love/hate thing depending on specific context. Average human ears are most sensitive to the 2-4k range so no wonder listening to that speaker can sometimes be a painful experience - it's exactly where the v30 screams the loudest.
The plot falls back to nominal level at 5k and drops off suddenly above that point. This is where things get really interesting, because treble attenuation is one vital purpose of every guitar speaker. Look closely at the slope and you will see a kink at 6k and another small one just before 7k.
At about 7.5k the plot bounces back up and that's where the funny noises are. If I remember correctly, Ola Englund uses an 8kHz low-pass filter on his guitar tracks. That way he kills the funny noises without affecting the speaker's natural roll-off.
"Trimming the tail" at that point helps when you're mixing for MP3 because its compression is going to turn those shimmering overtones into what sounds like rustling HDPE bags.
But when mixing for a high quality medium, those funny noises can be a nice detail, so there is nothing wrong with leaving them alone.
The effect of that 8kHz LPF is audible on some guitar tracks, which implies that guitar tone can span an even wider bandwidth.
I am still quite shocked by Drex's plot though. Cable tonesuck is nothing new to me, but these cords are several feet long, so be it. But tone sucking pickup hookup wire doesn't smell real good, I'm telling ya.
