Whoever mixed "Death Magnetic" probably HATED Metallica as even the band acknowledged that the entire album was fucked in the mixing booth after the recorded it.
Death Magnetic was produced by the guy that singlehandedly destroyed countless of albums:

Rick Rubin, the loudness war kike. He mastered the entirety of SOAD's discography which is bricked to shit, he mastered RHCP's Californication which is regarded as one of the loudest album ever, and Death Magnetic is the magnum opus of this brainless kike retard. Corey Taylor was 100% right about him when he had the displeasure of working with him on Vol. 3.
Now that I've started I'm gonna go off on a massive tangent, so get ready for a wall of text.
This is a site I tend to visit whenever "shopping" for albums. You look up a band, an album or both and you can see the DR, or dynamic range values.
For example:
https://dr.loudness-war.info/album/view/198287
Dire Straits - Brothers in Arms, the original pressing from 1985. One of the best CD albums ever released. All in digital, with album DR of 16, with So Far Away reaching DR of 20.
Now let's look at a modern "remaster" of this album from 2005:
https://dr.loudness-war.info/album/view/167147
Yep, max DR is lower than min DR on the original pressing. Completely destroyed the quality of the recording.
But what does it mean for the sound quality anyway? Well let's compare the unmastered version of Death Magnetic from Guitar Hero 3 to what it became after Rick Rubin thoroughly raped it with his circumcised Jew cock:
This is the most extreme example of what the loudness war does to sound. The snare is gone, because it's always the instrument that pops out the most on recordings, and there is audible distortion. Why does that happen? This video explains it best:
Dynamic range simply means the difference between the quietest and loudest sounds in the tracks, like the most prominent snare. When it's bricked, it's as loud as everything else, so the DR is low and it sounds like shit. When it's not, it's much louder than everything else, so the DR is high and it sounds good.
People at RuTracker.org tend to restore loud albums, which is to process them in a way to try and undo the damage done by people like Rick Rubin. I have a habit of downloading those but I never did a reliable test to see if I can actually hear the difference, but hey ho, whatever.
Now, do keep in mind that this is useful when comparing digital copies. In case of vinyl records, the DR metric isn't comparable to the one of the CD Audio, which is best explained on the HydrogenAudio wiki:
https://wiki.hydrogenaud.io/index.php?title=Myths_(Vinyl)#Effect_of_vinyl_mastering_on_dynamic_range
This is the most important part of audio quality. Garbage in, garbage out. If you play a bricked master, it'll sound like shit on all output hardware. A high DR MP3 will sound better than a low DR FLAC.
Now while we're on the topic of audio formats, you only really want to use FLAC as a means of archiving audio. The 16-bit 44.1kHz quality of Audio CD is enough for 99.9% of people to listen to music at it's best, anything beyond that is diminishing results, so keeping gigabytes of FLAC files on your smartphone is silly. And it's very important that the sound in the FLAC file is in fact high quality. Again, garbage in, garbage out. You can encode a 128kbps MP3 as a FLAC and it'll still sound like a 128kbps MP3, but will take up way more disk space.
However, MP3 is a terrible format due to it's harsh compression that in some cases is in fact audible. Thankfully nowadays we've come a long way and we have the ultimate file format for low file size, high quality listening. That format is Opus from Xiph.Org Foundation, the same people that gave us FLAC and OGG Vorbis. What makes Opus interesting, is that at 128kbps it's transparent, meaning that it's audibly the same as lossless while taking up less space, even less than a 320kbps MP3 while having better quality.
And speaking of audible, the most important thing at play in all of this is psychoacoustics. In the end you're replicating soundwaves that go into your ear, and your monkey brain can do a lot of weird things. It doesn't see bits, bitrates or anything like that. It just perceives moving air. That's why blind A\B tests are the most important in all of that. When you know what you're listening to, you'll have a predisposition to judge it by what you know and not what you hear. Just about every idiocy in this hobby stems from this issue, people
think they hear a difference but they can't even measure it.
AND SPEAKING OF MEASURING, this is the other side of the audiophile hardware community. People who scientifically measure sound equipment to judge whether or not it's good. One of the biggest forum about it is
Audio Science Review, ran by Amir Majidimehr, an electrical engineer. He measures a variety of audio hardware with measuring equipment worth thousands of dollars to judge it's quality. This is the most sane way to look at it, but at the same time you can become susceptible to buying more and more expensive hardware because it has better measurements, forgetting about this thing called psychoacoustics.
In this post, Amir has nicely explained what all those measurements mean and what they mean for audio quality in digital to analog conversion. To put it simply, you buy better equipment to reduce imperfections of the process. You don't start from perfect and go from there, you start from crap and you try your best to move away from it. At the same time, just because something is a known expensive brand doesn't mean it's good. Something like a Topping DX1 is a rather affordable Chi-Fi DAC/AMP combo that is considered to be one of the best in it's price point when it comes to the DAC accuracy. Plus it packs some punch to drive those high ohms studio headphones from a mere USB 2 connection.
As for headphones, yes, there are also measurements of how headphones reproduce sound and you can technically judge their audio quality by it. The aforementioned Harman target curve is what our monkey ears want to hear the most, and the closer a pair of headphones is to it, the better. It's not an absolute metric of course, because in the end personal preference is the biggest deciding factor, but it helps to see if a given pair of headphones has a major sound quality issue that makes it sound wrong.
There are also aspects like open vs closed backs. Open backs have less bass and don't isolate sound in any way but have a better sound stage, or locality, where the sound doesn't feel like it's coming directly from the headphones and it can sound further away or even behind or in front of you, which is the type of sound some people might prefer. There are also closed backs, which give you dat bass as they isolate, form a tight seal, at the cost of the lack of the sound stage, where everything just gets tunneled directly into your ear. Sound is an airwave, open backs let it go free which is how we hear everything while closed backs force it into your ear. As for ohms and sensitivity, this is a whole bunch of power math, but the most important thing to know is that a "demanding" headphone will need more power from the source to play it at a given volume. But if you're sane and don't want to go deaf, this isn't too big of a worry.
There's a whole lot more I could ramble about like speakers and IEM's and other technicalities but the most important takeaway from all of this is that there are various extremes in the hobby, and there are many variables when it comes to digital audio quality. But once you learn all of it, you can find your middle ground and settle for something sane, in your budget, availability and preference.
I would love to get deeper into the hobby but I don't have the cash to spare to start buying things left and right. As of now, I have a pair of Beyerdynamics DT990 PRO 250ohm with a shitty old USB audio interface that works, and I'd like to change it for something like the Topping DX1, but at the same time I would need to train my ears to know if that would even give me a real difference. But I'm happy with what I have right now, at most I'd get a pair of DT770 PRO's to have a set of isolating closed backs with a thump. Beyerdynamic is one of the old studio headphone companies that didn't sold out and still make their shit in-house in Germany, and they're comfy and built like a tank. The PRO models are the ones designed for serviceability in studios, but they also have the 3.7m coilspring cable and a tighter head spring some people dislike. There's the EDITION model that's less serviceable, has as straight cable and a lighter spring for consumers.
If I were to recommend you something to buy as a little gateway drug, I'd say get the Koss KSC75. Yes, the fugly clip-on headphones that Etika had and that DarkViperAU uses. Don't question how they look or little they cost or what lolcows had them, just buy them blind, you won't regret it. They're the gateway drug into the "clarity headphones", placebo bass thanks to the clip-on format, and the rest is fantastically fine tuned so you really hear all the details. They're also great as gaming headphones, no joke. There's so much more I could ramble about for days because this is one of the topics I'm really into besides the general IT shit.