What does a tonearm contribute to the sound of a turntable?


Curious about how a tonearm affects a turntable sound. I guess it's the piece of the turntable I know the least about and feel the least connection with. how does a really good tonearm affect the sound or not affect the sound? And what about the tonearm does the affecting?
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Larry needs to gain some experience  and knowledge before comparing a high end vinyl rig and quality acetate to the sound of a telephone.  That’s like comparing Lawrence Olivier to Popeye, or Raquel Welch to Phyllis Diller.  
Vinyl just has that tubey magic, well that’s what the guy @ better records proclaims! Lol...I love my vinyl and my many lp’s and phonographs...and you will have to tear them all from my dead cold hands! Streaming is for the lazy...jmo...its fun for discovering etc. But when I’m serious, its vinyl. Right now, I’m liking my pro-ject 9 inch carbon fiber/aluminum sandwiched tonearm with tpe damped counterweight on my classic sb table with a Hana EL moving coil, it sounds great with very little noise...put on the right record and its heaven...even though it’s not comparable to some other's mega buck analog rigs, to me, for now, it sounds divine. Not to mention, the classic is a joy to look at and use.
Right arm makes big difference I upgraded to dynavector 507 mk2 on my avid Acutus and wow , if I could afford to get higher end equipment I could go for it without hesitation , because for sure It will sound better and you can definitely hear it .
btw digital is like a kiss trough the glass compared to vinyl 😎
I went from various iterations of the original SME 3009 arm to various VPI arms including two of their 3D arms to my current two arms, Reed 3P's.
I have had 9", 10.5, and 12. Steel, alloy, carbon, plastic (VPI 3D, call it "composite" if you like, it's junk IMHO), and now one Reed is 12" cocobolo and one is 10.5 in ebony.


@fsonicsmith welcome to the club, i have the same Reed 3p Cocobolo "12 :)) Wonderful modern High-End tonearm. I've met people from Reed in Vilnius, Lithuania to get my sample. It's definitely a top quality tonearm. Then i went to vintage route and it's an interesting journey with tonearms like FR-64fx and 64s, Lustere GTS-801, Technics EPA-100 MK2, Ikeda IT-345  
With the new Jelco, I now have not one, not two, but six signal interfaces between the cartridge and the speakers:
  1. cartridge to headshell/arm
  2. headshell/arm to Premiere Interface DIN (little box on the back of the VPI - which I desperately want to get rid of)
  3. Premier Interface DIN to RCA
  4. RCA to phono pre
  5. Phono pre to amp
  6. Amp to speakers
Is this normal?