Dedicated circuit

@OP,
I see you also have fluorescent lighting.
I think that as well as the compressor will be another reason to put a separate line to the stereo.
I would like to run a subpanel from my mains, but, due to living in a 100 year old home, there isn't space to add one. Even enlarging the panel has problems.
B 

What size breaker does the subpanel use?
50amp  6ga wire
I agree. I will run from main panel

I think you should run the audio from the main panel. The subpanel has the compressor and power tools which can add noise and affect current draw.
On the main panel use a 20A breaker wired to the opposite leg of appliances and the subpanel (even though the sub uses a dual breaker).
Let's see what jea48 says.

What size breaker does the subpanel use?

I’m not @jea48, but until he chimes in, I can tell you that I run a compressor as part of my hi-fi system-- fairly substantial, at one point a 1 hp 13 gallon unit- but even with smaller units, there was a nasty electrical snap that could be heard through the system when the thing cycled. The way I resolved that at the time was to run it from a 240 line with a step down transformer.
When I moved, I had more flexibility and installed a dedicated line just for the compressor that went nowhere near the subsystem feeding the hi-fi. The hi-fi has it’s own iso tranformer (10kVa- a beast) that runs to a sub panel that feeds 10 gauge Romex to the outlets. The compressor is not coming off that big iso transformer but comes from the main panel for the house and has a smaller iso transformer as a buffer.
You are probably creating a little bit of racket in a hot rod shop, but it’s worth checking to see how much noise you hear through the system when things are quiet. That "snap" was quite pronounced for listening purposes in a quiet, dedicated room. Dunno if that helps. Love to hear about the hot rods though!

Wish I could have chimed in earlier and clarified things before assumptions started.I do thank all who replied.  First off it's an air compressor. My stereo setup is in my shop. I build hotrods so I apologize for just saying compressor. It's a garage thing I guess.I have a 200 amp main. Subpanel feeds most of my shop: T8 lighting, outlets, 220 for air compressor, some kitchen lights and an outlet or two. kitchen appliances have their own off the main.I don't need ultra highend hookups, just a solid clean power source. I've done plenty of wiring in my 61 years, helped out by a now retired electrician.
I can tell you what works to build a street friendly 800 HP engine, but not wiring upgrades/tweaks that have been proven to work. I don't sit and listen to every little detail in any music. My system is in my shop. So it's where I jam out. Just got me some ForteIII's and everything from Buddy Guy to Robin Trower hits hard.

@jea48 .
The OP says his line comes from a subpanel that also has the AC compressor.
Would it make sense to simply add another subpanel from the main?
Would that isolate the effects from the AC unit?
(OP-sorry if I am making this more expensive. I only want to see if there is a way to keep the AC from affecting your stereo).
Bob

To me 3 wire is,for example, 12/3 w/ground.
so I could run 12/3w/ground tie the hots together and end up with an effective gauge of 9

 The 3 wires would be hot (black), neutral (white) and ground. I would at least have a double outlet box, 4 sockets pig tailed.

I plan on running 2 outlet boxes to my room. One outlet box for my amp with 2 sockets on the front wall. And then a 4 socket outlet box for my components on the side wall. I don't need 4 sockets right now, but in the future I may. It is easier to put in extra now than have to add outlets later. I am going to use some PS Audio outlets I have lying around to start. So the dedicated outlets in the room will be light grey, while the rest of the outlets in the room are white.

Unfortunately, the ac compressor is going to infect the whole house, it won’t be confined to the subpanel. Running a 100 foot branch circuit makes it a magnet for EMI generated throughout the house, so I would use 3-wire romex. The wire is pre-twisted and helps with rejecting common mode noise, which could be a problem at that distance.

So, I assume using 3 wire I would combine the two hots, giving me an effective gauge increase.
At this point I am only installing one outlet for my amp.

+1 for jea48 and gs5556

+1 for Jim also..

Unfortunately, the ac compressor is going to infect the whole house, it won't be confined to the subpanel. Running a 100 foot branch circuit makes it a magnet for EMI generated throughout the house, so I would use 3-wire romex. The wire is pre-twisted and helps with rejecting common mode noise, which could be a problem at that distance.

I concur with jea48.

If I were to get an answer from @jea48 ,
I would take it as gospel.
Just do a search of his responses over the years and you can see why he is trusted-almost as much as the late Almarg.
Bob

Hey skids, ask these geniuses what their advice is based on. I’ve installed panels, sub panels, wired my house, wired my listening room three times, first with a conventional circuit, then direct 4 ga, then had that cryo’d, then converted it to 220V with a step down transformer, then treated the whole length from panel to conditioner, which I’ve modified. So if you ask me something and get an answer from me I actually know exactly what I’m talking about- including how valuable it is in terms of cost vs sound quality.

Reason I say this is the first advice is completely erroneous, and the second while technically not bad isn’t really any help either. Its just there’s a long history of providing incredibly detailed informative advice that gets swamped out and ignored in the crapstorm of irrelevance like what you already started. So you want help, ask me. Otherwise, I am outta here.

Hi skids,

Run it from the sub panel and add a panel surge protector. This won't reduce noise but prevent any motor induced surges from getting into your gear.

Best,

Erik