Do Higher MP3 Bit Rates Pay Off?

In a tidal shift akin to the Sexual Revolution, the heyday of Napster (that’s 1.0) markedly changed Americans’ perceptions of intellectual property rights and fair use. Some folks considered the music-swapping orgy a shameful, lawless epidemic of hedonism that would inexorably lead to social and economic chaos, while others considered it a thrilling, lawless epidemic of hedonism that liberated all of us from the musty stench of an increasingly bland and commercial culture. But everyone understood one thing: MP3s were here to stay.

Back then, most MP3s were encoded at constant bit rate (CBR) 128Kb/s, striking a balance between acceptable audio quality and file sizes that were small enough for easy trading over a dialup connection. But what was born out of necessity endures today, as most of the music available on rogue peer-to-peer networks is still compressed at this rate. It’s been called “near CD” quality, but we know better—it isn’t even in the same Zip code as CD audio.

But at what point do higher bit rates stop paying off and simply take up too much space? 160Kb/s? 192Kb/s? And can a hardcore audiophile really tell the difference between a 320Kb/s track and an uncompressed one? What about a normal music listener?

These are the questions we wanted answered when we set out bear traps around the office and came back later that afternoon to retrieve the snared employees. From the bunch, we selected four representing a range of musical tastes and quality demands. We handed them headphones, pressed the play button, and got some surprising results.

How We Tested

Each lucky participant was asked to bring in a CD with a track that he or she has listened to for years and knows so intimately that a single missing hi-hat tap would stand out like a sudden blast from a tuba. We ripped each track using iTunes at three quality levels: 160Kb/s, 320Kb/s, and uncompressed WAV. The compressed files were ripped using variable bit rate (VBR) encoding, meaning that a 160Kb/s VBR track allows the bit rate to rise and fall depending on the complexity of the music while maintaining the selected bit rate as the minimum bit rate for the track.

In a quiet room with mood lighting and kitschy Scandinavian furnishings, the participants put on a pair of Sennheiser HD 580 headphones that were attached to our test PC’s Creative X-Fi soundcard. The participants listened to not only the three versions of their own track, but also the three tracks from each of the other participants, for a total of 12 tracks in all. Each participant was allowed to listen to each track as long as he or she could stand it, and was allowed to repeat portions of the track and do A/B testing with the other tracks.

How Good is Your Encoder?

The thing that most often fools newbs is not knowing what kind of sounds are evidence of bad encoding or heavy-handed compression, but there are a couple tracks you can throw at your software to see how well it’s doing. Of course, you should begin with uncompressed files, so you can’t download these test tracks from an online service. If you don’t want to pony up for the CDs, you might want to check your local library.

The first is “Neon Reprise” from Metropol by Lunatic Calm. The song contains a whooshing upward sweep that audio compressors have a very difficult time with. Turn off Joint Stereo and keep upping the bit rate if you hear any warbling (like a cassette tape that’s been mangled).

The second comes from the legendary 1965 RCA Victor Opera Series recording of Verdi’s La Traviata. In Act II, Track 10, position 3:16, Anna Moffo belts out a bone-liquefying high note. Focus your attention not on her voice, but on the instrumentation behind it. If there’s any fuzz or rumbling in the background, again, dial up the bit rate.