Microphone equalization (guitar cab + Shure SM57)


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Hi all! I am recording the output of my guitar cabinet through a Shure SM57 which unfortunately changes the frequency content quite a bit. Is there any standard trick to equalize the tracks such that they would sound a little more like the actual sound of the cabinet? I thought that a simple "inverse" filter (or an approximation of it) would do the trick to some extent, but I cannot find much info about it :p I guess the easy, but expensive, solution would be use a Shure SM57 AND something like a Royer R-121, but I am interested in knowing how far one can go with a Shure SM57 ;)
I was playing around with this set up and thought it was neat.

Fender open cabinet- Use dynamic(SM57) in front 1-2' where speaker converge, and a microphone at the rear PHASE flipped to get the lows.

Screenshot 2022-05-01 112723.jpg

Marshall closed back- Use a Dynamic in front 'on the grill', slightly off the cone, and a microphone on the corner of the cabinet(phase flipped) for the bass.
Screenshot 2022-05-01 113008.jpg

Id use tight dynamics. My rooms suck. Then add ambient reverb. Multimic setup though.
The only thing that matters when you're recording a cabinet is what it sounds like through the monitors, thus on the recording. It's common to place the 57 right close to the grill cloth on the cabinet, which is not how it will sound in the room. It can help to get the cabinet away from large flat surfaces like walls and floors which can exaggerate the low end response (chair, amp stand, etc...).

One of the most powerful tone controls is mic placement. With the mic firing straight at the speaker, if you sweep it in a straight line from the center of the dust cap to the outer edge of the cone you'll get dramatically different response. Having the mic pointing at the edge where the cone meets the dust cap is a popular starting point. Tweak as necessary. Moving the mic in small increments like 1/2 inch or so will make a difference.

It's also fair game to tweak the eq controls of your guitar chain before you press record. You can always EQ slightly after recording the track, but being as close as possible to what you want on the way in is helpful.
Thanks for the input @LazerBeakShiek and @snow lizard! Apart from mic placement and adding additional micorphones (which are options I am aware of, but surely haven't fully explored yet), I was wondering if something like this
is a viable method. I will play around a little more with the mic placement in the meanwhile :p
You cannot make A 57 into a 121 with EQ or etc. No, the Eq is applied after the doorway (microphone) the signal has already been captured in a spectrum.
Whats a inverse filter? A HPF /LPF
Something slightly more complex than that, but basically a higher order filter that amplifies what the mic attenuates and viceversa. Of course you cannot get a perfectly flat response, but it should be possible to make some improvements.
Microphones aren't ears, and you don't have your ears pointing directly at the speaker cone, so the mic will never sound like what you perceive in the room. (especially if it is close mic'd) If you put your ear where you placed your mic, you would hear something more what the mic is giving you. (don't do this at war volume)

The fastest way to get a good sound recorded is to let go of what the amp sounds like in the room and focus on what it sounds like to the microphone. If what you are getting in the mic is too dull, aim the mic more toward the center of the cone, if it is too bright move it away from the center. Small mic movements make a huge difference in the captured tone.

Guitar 'sound' is made up of a few different things.

The feel of playing, which tends to be caused by the compression and response of the amp. Smooth or spikey

The tone structure or frequency response. This is the only thing you can manipulate with mics, mic placement, or EQ

The type of, or lack of, distortion. Crunchy, grainy, fuzzy

All of these are affected by the others and most of what people tend to want to capture is what they feel while they are playing, which can be completely different than what it actually sounds like to other people or the microphone. Much the same way your voice sounds different when recorded than it does when you are talking.

All this rambling is to say that you need to adjust the amp to capture the sound you want through the microphone without worrying what it sounds like live in the room.
What Farview said ^^^^ Also, the angle of the mic towards the speaker will make a difference, too.

If your room is well-treated acoustically (or large) you can also try pulling the mic back several feet from the cabinet, this is how George Martin (Beatles) liked to record amps, of course that was always in a good sounding studio.
I think many guitarists have the same issue - they want the same sound they hear coming out of the cab, but forget totally that they have never heard what an audience hears after the person at the sound desk 'treats' it. In your own studio, you have a mic, and you have EQ, so somewhere you already have your 'sound'. you just need to find it. It is there somewhere!
As ever, 'Aug 07 soundonsound.com. Perhaps THE definitive article on recording gitamps?

Then, the SM57 has probably been used on amps more times than all other mic models together, can;t really go wrong with a '57.
As Rob says it is the sound the 'punters' hear that is important. And don't forget, after 1/2hr with any gitamp close to full chat your hearing (and thus judgment) are **cked.