What is the least compressed signal?

Thank you all for your comments!

But don't get confused here. There are two types of compression being discussed. Both are important.

One type is file compression. It can be lossless or lossy. When it is lossy some of the 1s and 0s are left out. 

Dynamic range is another form of compression where the dynamic range is compressed. There are good links about that above. It is a plague with no purpose and no seeming cure. And the problem is that you don't know on which recordings it is worse. You can certainly hear it. But if you want to avoid it and know what you are buying then go to the DR database linked to above.

There are those (who know far more about audio than I do) who say you can tune your system to compensate for DR compression. But that sounds like putting lipstick on a pig if you ask me. When dynamic range isn't there........it isn't there and nothing you can do can get it back.

Cassettes had the worst DR of any source at the time. The main reasons were its slow speeds and tape width. I think it was the 70’s when I had the top of the line Akai cassette deck with servo buttons and glass heads which compared favorable to others like the nakamichi decks. I also had a teac 7” R2R deck with speeds up to 7.5ips. The teac was so much better sound wise. Then 10 years ago I got an Otari 5050bl with 15ips. For a 20 year old deck, Sound quality was fantastic. 3 3/4 speed sounded like crap compared to 7.5ips, and the 7.5 ips sound was flat compared to the 15ips. Speed for tape matters

The statement of the most previous poster is correct. Tape speed is most important as pertains to sound quality. Not mentioned thus far is 8 track tapes. Sure, they were large, clunky, and due to their poor construction they often ejected from their players with a stream of tape type confetti. But......
Their play speed was almost twice that of cassettes and, during their short lived lifetime, they sounded better due to tape speed in.ips. Cassettes were smaller and not prone to mechanical failures. Note.... Both of these recording mediums were primarily built for those who wanted good music in their cars.

The previous post about the 2 different types of compression is mostly relevant.
When you fear that tuner signal might be compressed you are talking about dynamic range compression. DR compression is really bad from the SQ stand point.
File compression not so much. There's a subtle difference bewteen a high quality compresses file and a non compressed one (or lossless compressed which is to say same quality as non compressed)
DR compression is immediatly audible instead and there's not really much you can do about it except go look for another source 
CDs as a rule are not compressed at all. They present the full Red book audio signal in non comprsssed format.
I am sure I added a lot of confusion, sorry about that . . .