In Search of the Lossless Chord

Confused about which audio codec to use to encode music for your portable player? Drowning in the alphanumeric soup of AAC (iTunes/iPod), MP3, and WMA (Windows Media Audio)? Want to guarantee that you'll get the best possible sound out of your hard-disk collection of ripped CDs?

Take the easy way out: Use lossless data compression. You won't be alone. Lossless encoding was at the heart of the DVD-Audio system, and the designers of the HD DVD and Blu-ray Disc systems have incorporated similar lossless multichannel schemes into those formats.

A lossless encoding system means exactly that: No sonic quality is lost during audio data compression because the original digital data is mathematically preserved and reconstructed bit-for-bit on playback. More familiar codecs such as AAC, MP3, and WMA - collectively referred to as lossy systems - don't precisely reconstruct the original signal, and they introduce additional noise and distortion into the sound. Given a high enough encoded bit rate - 128 kilobits per second (kbps) and higher - these defects can be well hidden. But even turning the bit-rate controls all the way up is no guarantee that the sound will be unaltered (harpsichords have traditionally been the killer instrument here).

Lossy systems are psychoacoustically based and compress data according to calculations of what is audible or inaudible in the original signal. Those parts deemed inaudible are discarded from the data (hence the "lossy"), and the remaining parts are recorded with as few bits as can be used while still keeping noise and distortion below the calculated threshold of audibility. Lossless systems work differently. They don't care or even know what is audible or inaudible. They base their encoding on the statistics of the audio signal's data. They make heavy use of "entropy" encoding techniques and are similar in many ways to lossless computer-file compression schemes - zip files, for example. Zip files have to be lossless because the alteration or omission of a single bit in a computer program of any size can render it useless.

In return for bit-perfect data, there's a tradeoff: On average, lossless systems have a compression ratio of 2:1, compared with 11:1 for a lossy codec running at 128 kbps. A 4-gigabyte (GB) portable player, such as an iPod Nano, will hold only about 12 hours of music encoded with the Apple lossless system supplied with iTunes. But if you don't ever intend to carry around your entire CD collection in a portable player, this may be a reasonable tradeoff for bit-accurate sound. At home, where the cost-per-GB of hard-disk space has been falling consistently for the past decade, the added space taken up by lossless encoding is far less significant - and the gain in sonic quality all the more audible in a listening room with low background noise. A 200-GB hard disk will hold about 26 days worth of losslessly-encoded stereo music.

All popular lossless encoders operate in similar ways, and they all achieve about the same 2:1 compression. Furthermore, a properly set-up comparison between lossless encoding schemes will consistently produce a result of "no audible difference." This greatly simplifies matters, and not necessarily to the advantage of encoder providers: They can't compete, like Dolby and DTS, on the basis of audio quality or encoding efficiency. The crucial differences among lossless systems are instead related to practicality - the complexity of the hardware and software to encode/decode the signal, the time it takes to encode a CD, and whether your portable player supports a lossless format at all. The vast majority of WMA-compatible portables don't support Microsoft's lossless version of WMA, for no particularly good reason.

That's too bad, especially because now there's a legitimate music-download site, MusicGiants.com, that encodes all of its music with the lossless version of WMA. The site could conceivably feed lossless-capable WMA portable players, in addition to helping you stock a lossless hard-disk library. (Lossless multichannel downloads are promised this year.) The sign-on fee is a relatively hefty $50, but you get it back in "free" downloads. And once registered, you can download albums and special collections of material from all the major labels, with the repertory ranging from the latest rock and dance hits to jazz standards and classical works.

If you want to know what MusicGiants' lossless downloads sound like without having to pay that sign-on fee, you can use Windows Media Player 10 to make your own lossless CD rips with the same encoding format that the site uses. The tracks will all sound precisely like the originals, as intended.

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