One of the problems with MP3, which I only became aware of when I read Monty Montgomery's lengthy paper about digital audio and sampling, is that MP3 files of the same density, say 128 Kbps, that have been ripped from the same source but with different ripping software, are not all of the same fidelity. In fact they can differ quite widely and there is no real measurement which can tell you that. The format itself does what it 'says on the tin' and carries sound data in a standard format which an MP3 player can interpret and convert into a PCM file to pass through a DAC. The transfer medium will have no effect on fidelity (unless its is faulty or badly designed) and neither will the unpacking software on your player or PC, but the DAC definitely will have an effect on fidelity and the more information it is given about the original sound wave the better it will perform. Ripping, or rather compaction algorithms, must be very complex, and there must be lots of different methods, little tricks that work etc., I haven't done much reading about them except the non lossy methods, enough to convince myself that they really are non lossy. So, unlike players (foobar, VLC, etc) which all do pretty much the same thing and don't affect fidelity, the compaction algorithms for lossy formats can make a big difference and Monty explains this very well. It is his job after all.
The compaction algorithms in the original MP3 ripping Apps back in the 90s were very primitive, so even at 256kbps they didn't do a great job. They have been gradually improving and modern compaction algorithms are far better because a lot of Mathematicians have worked out clever methods of compacting digitised audio waves in ways which retain more information. This will be easier to do the more processing power you have available. (This is why FLAC encoders allow you to select the compression level you want depending on how much time you want to allow your PC to spend working on it. With FLAC this doesn't affect fidelity, just the amount of compaction you can achieve.) I imagine that there are MP3 rippers which have a similar setting (not sure, I don't do it nowadays) so you can allow them to spend longer and capture more information at the same level of compaction. I have been told by a couple of friends that MP3 files from iStore sound better than those they have ripped themselves at the same density, and this is probably because nowadays commercial ripping is done using more advanced compaction algorithms running on a big fast computer which it is better able to exploit them.
If, like me, you have a random collection of MP3 files you have accumulated from various sources and ripped on various packages over the years, and you are the sort of person who reads this stuff, then you are probably thinking, '**** that means I really need to redo them all using blah blah software etc etc'. Or you can just start doing all your CDs again using FLAC at whatever compression level suites you, and not have to worry about whether the compression algorithms are good enough for your ears. You will never have to rip them again, if you keep a proper backup, because that is the best you can achieve with CD format, because it is lossless. So I agree, there seems little point in continuing to use MP3 if you are prepared to spend a little more money on some disc drives, SD cards, broadband speed (if you are streaming or downloading) and Home Ethernet (if you are streaming around your house).
The irony of this is that the reason all this clever audio compaction Mathematics has become 'surplus to requirements' is that somewhere else, I have no idea where, another group of clever Mathematicians have been working away on modulation methods. Their discoveries and the new techniques they have led to, have enabled an absolutely massive increase in the amount of data we are able to transmit and store. IMHO this is the first great technical advance (or 'wonder' ) of the 21st Century, and it appears that it is going to continue increasing at a similar rate for some more years, but it will start to hit some law of diminishing return eventually.
Elsdude says - 'For most people and most purposes somewhere around 256 or 320 kbps MP3 becomes indistinguishable from lossless.'
I agree with that and I think the only time it really makes a difference is when we are sitting and listening to music to the exclusion of all else. Properly listening and really absorbed in it, enjoying it and feeling it. We used to do that a lot but we don't so much any more. I certainly didn't for about 30 years.
Now if you are saying to yourself, 'well I get that feeling from MP3s'. Of course you do, you can get that feeling the first time you hear 'Be My Baby', whether it is on medium wave radio, an old Dansette, an MP3, whatever. And if you appreciate that and it is important to you (and you are in a small minority if it is) then you will get that feeling more intensely and with more enjoyment if you listen to it from a good non lossy source played through a good DAC etc. You will immediately notice that it sounds 'better' and if you then do the same thing with a really good vinyl pressing, (and there is a big long list of caveats about all the things that can be poor or can cause problems, so all of those have to be right), then you will immediately notice that it sounds 'better' again.
RRod -- if I haven't bored you to death? you know me already lol. You refer to 'until something akin to a sampling theorem'. Is this something that people discuss as a possibility? Has it been speculated about anywhere? or do you know if there is anything written about it???