Why your MP3s sound bad: high-resolution audio explained

 

Neil Young made waves this week with some comments about digital music files—first at the Sundance Film Festival, and then later in an All Things D interview. But lost in the media frenzy is his real point. Young wasn't putting down all digital music. Instead, he was referring specifically to the compressed MP3 and AAC files most people listen to today. Truth is, they just don't sound all that good.

 

It also turns out that despite helping to popularize digital music, Steve Jobs was a closet audiophile. Young said Steve Jobs was working with him, among other artists and engineers, on a method of delivering higher-quality files to consumers. This in and of itself isn't new; about a year ago, CNN learned Apple was in talks to make available 24-bit uncompressed music files in iTunes. But interestingly, Young also said Steve shared an interest in vinyl records, which have recently gained a new generation of fansdespite the format's overall impracticality.

 

The renewed focus on audio quality in some circles has a sense of déjà vu about it. Some of it recalls the 1970s, back when the term "high fidelity" was thrown around to indicate quality stereo recordings. We also saw this go around again at the turn of the millennium with the introduction of SACD and DVD Audio formats, which brought 24-bit fidelity and surround sound to audio mixes, although neither took off at the time.

 

So what's going on here? In a word, it's about data. More data translates to better-sounding audio files—but those files are largely unavailable to most consumers. Granted, to the casual listener, Amazon MP3 and Apple iTunes Store sound pretty good, as they're encoded as 256Kbps MP3 and AAC files for the most part. Amazon has some MP3 files encoded at variable bit rates, but most of them center around the 224Kbps to 256Kbps range. AAC generally sounds slightly better than MP3 when encoded at the same bit rate, although recent improvements in MP3 encoding algorithms have largely rendered this academic.

 

Aside from music purchases, 256Kbps is also iTunes' default encoding rate for when you rip audio CDs in iTunes (although you can change it), and it's the size iCloud uses to deliver tracks to other PCs or mobile devices on your network if you're a subscriber. I'm just using Apple products here as an example; Windows Media Player, Winamp, and countless other apps do similar things. Any way you cut it, 256Kbps files sound a lot better than ones encoded at 128Kbps, which is what Apple used years ago before it removed DRM from its iTunes Store tracks. Granted, 256Kbps files take up twice the space as 128Kbps files, but on today's devices, that usually isn't a problem, and the improved sound quality is worth it.

 

The thing is, 256Kbps still isn't enough. Higher-resolution, uncompressed, 16-bit audio files match the sound you get on an actual CD. 24-bit sound files even sound better; the increased headroom matches the format most artists and mix engineers have been working in over the past decade or so.

 

Cheap consumer electronics manufacturers abused the phrase "CD-quality" for many years, but in this case it still has meaning. True CD-quality files take up anywhere from three to 10 times as much as space as an MP3 or AAC file, depending on the latter's bit rate; 24-bit files take up even more space. They come in several formats: FLAC, WAV, AIFF, and Apple Lossless. (FLAC and Apple Lossless contain some data compression but only in a method that doesn't affect sound quality. FLAC is much more widely supported than Apple Lossless, though.)

 

At this point, there are two main issues with uncompressed audio files: space and bandwidth. Hard drives are getting cheaper by the day. But mobile devices are still constrained by the capacity limits of flash storage, and the recent move towards non-mechanical, solid-state drives in ultrabooks also puts a pinch on available space. Download times are also a concern; it takes much longer to download an uncompressed album than it does an MP3 file, straining broadband connections and putting a damper on the recent surge in cloud-based sync services from Amazon, Apple and Google.

 

More Data Means Better Sound Quality
Okay, so bigger files sound better, but what does that really mean? Young said in the interview that when an artist creates something, the master could be 100 percent great, but the consumer is only getting 5 percent of it with an MP3 file. That's mostly true in absolute terms—a 128Kbps MP3 file can take anywhere from one-tenth to one-twentieth the space of an average raw, uncompressed CD track. Professors in professional audio programs have a trick lately of showing students what happens when you take an original waveform, overlay an MP3 version, and then strip the MP3 data away; you still see a lot of audible data left: This is how much you're losing with MP3 files!

 

In reality, most of the crucial data is there—enough to give a convincing, if not particularly pleasant sounding, representation of a recording. For most listeners most of the time, especially when they're listening while doing other things, this is plenty. The MP3 codec's impressive compression was shocking enough in the mid 1990s to eventually become the standard, as it far surpassed the sound quality of anything available up until that point.

 

But with a decent set of speakers or headphones that you're familiar with, if you listen closely, you'll hear the problem—especially if you compare it back to back with the identical CD recording. There are real differences in an MP3 file that mar the sound quality: Slightly softer bass response that veils some of the detail between a kick drum and bass guitar playing together; washy-sounding drum cymbals that, at the lower bit rates, sound almost like a phaser or chorus effect is applied; smeared transients that blur an instrument's attack, sustain, and decay. It gets more noticeable as you go from the low end to the high end of the frequency spectrum, too. A lot of the subtle details the artists and mixing engineer puts into a recording are diminished or disappear entirely in an MP3 file. Even 256Kbps (and yes, 320Kbps) files are still audibly different than what you hear on a CD, although at least those are somewhat closer to the mark. As you can imagine, this dumbing-down of sound quality drives everyone on the creation end nuts, but it also diminishes the listening experience on your end.

 

Switch to a FLAC file, and all of the above flaws go away. Sure, on a $50 set of computer speakers or the ones built into, say, an iMac, you're not going to hear this. Stock iPod earbuds won't do a lot for uncompressed audio either. But upgrade to Shure or Etymotic earbuds, or Bowers & Wilkins or Paradigm speakers (to pick just a few brands as an example—there are many more), and you'll begin to hear details you may never have heard before, even on familiar recordings. Stereo sound fields become three dimensional, with a sense of depth and space. It sounds as if a veil has been lifted; everything has more definition and natural sound. Cymbals decay properly after being struck with a drum stick. You don't just hear the finger plucks on an acoustic guitar—those come through over just about any speaker—but also the individual string and sliding finger noises too, as well as the warmth of the guitar's hollow wooden body.

 

Vinyl and the 'Old High-End'
So how does vinyl fit into all this? Things get a little tricky at this point, as there's plenty of vitriol between vinyl and CD listeners to go around. It's enough to set rabid fans of either format at each other's throats in Internet forums. So at the risk of someone in the comments telling me I couldn't hear a guitar solo if Mark Knopfler hit me over the head with a Stratocaster, I'll try and explain what's going on.

 

Vinyl is a conundrum. On the one hand, it's an imperfect, distorted medium with limited dynamic range, and it requires constant maintenance (cleaning, new cartridges on the turntable, and so on). It's also not portable in the slightest, unless you're a DJ with a bunch of crates and a big van. On the other hand, vinyl is tangible. You can hold it. It has large artwork. Most importantly, it has a beautiful sound that, with the right turntable, cartridge, amplifier, and speakers, can convert just about anyone who hears it into a believer.

 

The thing is, vinyl's various playback distortions are what make it sound great, from the more limited dynamic range, to the warm-sounding frequency response curve, and even in the way music was mastered to take maximum advantage of the pressing process. The age-old argument for vinyl fans against the CD (and, by extension, uncompressed data files) is that a CD contains the data representing a waveform sampled 44,100 times per second, in "steps," and that the rigidness of this algorithm could only approximate a smooth analog waveform without ever equaling it. That's not how CD works, though; instead, the D/A converter (digital to analog) interpolates the spaces between the steps and makes a smooth curve. Old CD players and PC audio cards sounded brittle, "clinical," and harsh because of early, imprecise D/A converters. Even today, high-end audio fans debate the sound quality of CD players, external D/A converters, and even the cables, all in an effort to get as smooth and detailed sounding a presentation as possible.

 

FLAC and the 'New High-End'
Several services have cropped up that sell uncompressed FLAC files directly, including HDTracks,Magnatune, Zunior, and The Classical Shop, albeit at a premium in some cases. Some artists have also made uncompressed versions of the music available direct from their Web sites. The Beatles are selling a $300 boxed set with a USB drive containing 24-bit FLAC files for all 14 albums. Trent Reznor released uncompressed versions of his four-part album "Ghost" on BitTorrent (which is an awesome distribution mechanism for huge piles of data).

 

Despite all of this, uncompressed audio has yet to hit the mainstream. The way things are going with mobile devices and digital sales, a lot of mixing engineers, musicians, and audiophiles worry that people don't realize what they're missing, and that true high-end sound will be lost forever.

 

I doubt it will ever come to that. Too many people are interested in quality audio, and emerging technology will only make it easier to access it as time goes on. In most respects, the MP3 and Internet radio revolution has been wonderful for music; it makes it dead easy to listen to as much music as possible at all times. I'd love an easy, integrated way of purchasing and listening to uncompressed digital music again. But now that I've largely moved away from CDs, I no longer want to buy one, bring it home, rip open the plastic, and spend 20 minutes importing it only to end up with wasted plastic just to get the top-quality sound files. It's a huge waste of both time and materials.

 

At the same time, the "music listening experience," such as it was, has changed a lot recently. For music fans, it used to be a lot about assembling just the right group of stereo components and speakers, having everything set up the correct way, and listening in the "sweet spot" right in the center, often to entire albums from start to finish. Not everyone did all that even years ago, obviously, but this is one of the things today's new vinyl enthusiasts have stumbled on and enjoy as part of the experience.

 

Uncompressed audio can deliver that same awesome experience. It's not about money, either. A Samsung Galaxy Nexus or iPhone 4S with a $150 pair of earphones can sound amazing. The Harman/Kardon SoundSticks III 2.1 speakers deliver unbelievably clear sound, and they're routinely sold for less than $150 for the three-piece set. If you still have a component-based stereo or are thinking of setting one up, so much the better. But in all of these cases, you'll need uncompressed audio files for the full effect. Now that people are streaming 720p high-definition video over the Internet, we clearly have the bandwidth for uncompressed audio as well. Here's hoping Neil Young isn't alone in what he wants out of digital music.