Poke around the Internet a bit and you'll find no shortage of opinion on music sources: CD vs digital downloads vs vinyl, etc. Which is best? The answer is: source doesn't matter, it's the mastering that makes the difference. Unfortunately, the vast majority of listeners don't realize they're getting screwed on quality. Let me explain...
The Loudness War
Have you heard of the loudness war? No? Don't worry, you're not alone. Most people haven't. Here's a short synopsis from Wikipedia:
"Loudness war" or "loudness race" is the popular name given to the trend of increasing audio levels on CDs and in digital audio files since the early 1990s, which many critics believe damages the sound and reduces listener's enjoyment...Modern recordings that use extreme dynamic range compression and other measures to increase loudness therefore can sacrifice sound quality to loudness. The competitive escalation of loudness has led music fans and members of the musical press to refer to the affected albums as "victims of the loudness war".
There are many (many) examples of "remastered" CDs with horribly increased levels, losing detail and dynamics in the process, and most (but thankfully not all) new releases are mastered with horrible levels to begin with.
Here's a short video that demonstrates this phenomena very clearly:
And here are two images (from the Wikipedia article) that show how two songs (Michael Jackson's "Black or White" and ZZ Top's "Sharp Dressed Man") have changed for the worse with each subsequent re-release:
The side affects of mastering (or re-mastering) for loudness are a loss of dynamic range, clipping the loudest portions of the song, and increased distortion.
Why do audio engineers do this to perfectly good music? There are many theories, but more than enough evidence that it's done at the demands of the record companies, who want their music to sound louder when it pops up on your portable music player, car stereo, etc. It's similar to how big box retailers put all of the TVs in the showroom on the "Vivid" setting to make them stand out, losing detail and color accuracy in the process.
Now that we've seen how mastering affects sound quality, let's look at different sources for music to see if there's a difference.
What does this have to do with music sources?
Like I said at the beginning, there's no shortage of arguments about which source format is best: vinyl, CD, digital download, etc. Is one inherently better? Not really.
Many audiophiles will argue that vinyl is best, that it has a "warmer" more analog sound, and is higher quality than CD or digital download. Is it true? Yes and no. It's true that many vinyl recordings (both old and new) sound better than their CD or download counterparts. This has nothing to do with the quality of the medium (vinyl), and everything to do with the fact that most vinyl recordings are made from an uncompressed master. In other words, they have not fallen victim to the "loudness war".
Here are the dynamic range values for Michael Jackson's "Dangerous" album (which includes the song "Black or White"). Notice how the original vinyl release has more dynamic range (less compression) than the original CD release, and how the 2001 "remastered" CD is just horrible:
So, yes, the vinyl version is the "best" when it comes to dynamic range, but not because it's vinyl...it's because it comes from a better master without loudness compression.
Vinyl has made a comeback in recent years, and many new releases are now offered in vinyl in addition to CD and digital download. In most cases, the vinyl version is mastered the way the artist and engineer want, while the CD and digital versions are compressed for loudness the way the record company prefers. Here's 2013's "Sound City" album:
Again, the vinyl version has more dynamic range due to less compression.
So, is vinyl always better because of better, less compressed masters? Not always. Have a look at Nirvana's "Nevermind" album:
Notice the original 1991 CD release is every bit as dynamic as the 2009 vinyl re-release, and the 2011 "remastered" vinyl release is horrible (as are the 2011 20th anniversary CDs and the 2013 Blu-Ray release). This is a perfect example of how source format doesn't matter: it all depends on how it's mastered.
So, are all CDs bad?
No. Only CDs that have been highly compressed and mastered for "loudness" are bad. There are plenty of good CDs, although most of the good ones are from the 80's or early 90's before the "loudness war" was in full swing.
A quick note about DR scores
The DR (Dynamic Range) scores I posted earlier come from an online database, the Dynamic Range Database. DR scores should be taken with a grain of salt, and not used as the be-all-end-all "score" as to what versions sound best. A well mastered source, even with some "loudness" compression added, can sound fantastic. A great example is the CD "Random Access Memories" from Daft Punk. The CD has a DR score of only 8 (the lowest number most people consider acceptible). But, it sounds much better than most CDs with such a low score, and better than some with higher scores. How is that possible? The engineers were very selective in how they applied the loudness compression, and they were able to produce a CD that sounds better than its DR score would seem to indicate.
There have been a host of so-called "hi-def" sources over the years: SACD (Super Audio CD), DVD-A (DVD-Audio), Blu-Ray Audio, etc. These various formats tend to offer music with higher bit-rates than traditional CDs, and sometimes also offer multi-channel surround sound. In many cases, these tend to be the best versions available because they were mastered from the original recording without added loudness compression, but without the clicks and pops that come along with vinyl. But be careful...sometimes these releases are wolves in sheep's clothing.
The record companies have a bad habbit of releasing new "hi-def" versions of existing albums, but use a crappy re-mastered version as the master. That's the equivalent of taking an original piece of art, making a photo-copy, then scanning the photo-copy and saving it as an "uncompressed" hi-resolution file format such as TIFF. It makes no sense. Sure, you'll have a "hi-res" version, but of a crappy photocopy, not the clean original. Before buying any of the so-called hi-res versions of an album, be sure to search for reviews to see if they were made from the original master and not a crapp re-master.
For example, the Blu-Ray Audio version of "Breakfast In America" was apparently mastered with one of the lower quality re-masters rather than one of the higher quality versions. In contrast, Beck's "Sea Change" Blu-Ray Audio release is regarded as exceptional - the best version of that album available in any format.
What about digital downloads?
Digital downloads also rely on the quality of the master, but introduce another layer of complexity: file compression. File compression is different from compression introduced during mastering, having to do with how much (if at all) the actual downloaded file is compressed to save space. There are three basic types of file compression: uncompressed, lossless compression, and lossy compression.
There are various file formats that don't compress the original source at all, including: WAV and AIFF (the two most common formats for uncompressed audio). The downside to uncompressed files is they are very large, eating up your disk space in a hurry. For that reason, many audiophiles prefer to use one of the various lossless compression formats.
A lossless compressed format stores data in less space without losing any data. The file takes up far less space than un-compressed, but retains all the original information. The file is un-compressed back to its original state by the playback device. Examples of lossless compressed formats include: FLAC, Apple Lossless (ALAC), WavPack, and Monkey's Audio. The two most popular are FLAC and ALAC. FLAC has wider support among playback devices, but those in the Apple world (those with iPod's and iPhone's) can use ALAC. More manufacturers are now supporting ALAC as well, including many streaming servers and AV receivers. iOS devices don't support FLAC, however, so your choice of format really comes down to what product(s) you use.
Finally, the most widely used file formats are "lossy" formats that get the file size even smaller, but at the expense of throwing away various bits of data. The more compression used, the more bits that are lost. The most common file types of lossy compression are MP3 and AAC. These are what you get from the iTunes store, Amazon MP3 store, etc. The quality of the final product simply isn't as good as with lossless compression. My take is that hard drives are cheap these days, so use lossless compression.
While the mainstream download sites (iTunes, Amazon, etc.) use lossy compression formats, there are some that sell music downloads using lossless compression and even uncompressed. The most popular site being HDtracks.com, which sells downloads in uncompressed AIFF and WAV as well as lossless FLAC and ALAC.
There's been a bit of controversy surrounding HDtracks because not all of their offerings are using the original un-compressed masters. This is the fault of the record companies (once again), not HDtracks. So, a little bit of due diligence goes a long way before spending your hard earned money. There are many great titles available on HDtracks using the original master recordings, not compressed re-masters. Look for reviews before buying and you'll be fine.
What about streaming services?
At this time, all streaming services are serving up highly compressed versions. Some are offering slightly less compressed versions if you sign up (pay) for a subscription, but none are offering lossless versions. Does it matter? I listen to Spotify (subscription version) every day at work. Since I'm listening with relatively cheap headphones, it doesn't make a huge difference. The music is basically background noise. Since I'm not doing any critical listening, I'm less concerned that I'm listening to crappy "loudness" masters that have file compression as well. But I don't listed to streaming music through my home stereo (even though it's available), and I'm in the process of re-ripping my CDs in a lossless format and will be making them available on a personal cloud service, so I can stream my own lossless music. I'll still use Spotify for new music discovery, however. If I find something I really like, I'll seek out the best format and buy it.
I know this was a long post. If you made it this far, hopefully you have a better understanding of how the record companies have been giving you sub-par products for decades. Demand better!