Q: I have a second-generation iPod nano and I have recently purchased an 80 GB iPod classic for home stereo use. I want to transfer the existing nano iTunes playlist to my new classic but, once transferred, I also want to convert the songs in that playlist from a 128 kbps bitrate to Apple Lossless for better sound quality. Does it matter, in terms of sound quality, whether I carry out that conversion using the iTunes preferences or would it be better for me to re-digitize my entire CD collection to iTunes from scratch?

- Parker

A: This actually matters a great deal. Converting a 128kbps audio file to any higher bitrate will not result in any improvement in sound quality—merely a larger file size at the same quality. In other words, there’s no point in even bothering to do this—you won’t get any improvement in audio quality.

Low bit-rate audio formats such as MP3 and AAC accomplish their small file sizes through the use of what is known as “lossy” compression. Essentially this means that the music track is analyzed, and certain audio content is discarded completely from the resulting file. Most of the time, this discarded content is in frequencies that cannot be heard by the average person using average equipment, and therefore is unnoticeable by most people. Of course, the higher the bit-rate, the more information is retained, which is why there is much debate about the quality of different bit-rates—something that is almost always a completely subjective decision based on your own ears and the equipment that you are using to listen to your music.

For comparative purposes, an original CD audio track is encoded at 1,440 kbps, or 1,440,000 bits of data for each second of audio. On the other hand, a 128kbps MP3 file only contains 128,000 bits of data for each second of audio. This means that in a 128kbps MP3 file, you have effectively lost 1,312,000 bits of information per second. This has been stripped out of the resulting MP3 file during the initial conversion process, and is never coming back. Therefore, converting this 128kbps MP3 file back to an original CD audio track is basically going to insert 1,312,000 bits of dead air into each second of audio—you’ll end up with a larger file with no actual increase in sound quality. In short, you can’t get data back that wasn’t there in the first place.

On the other hand, as their name implies, lossless formats such as Apple Lossless compress the audio stream without losing any data. The result is a smaller file at the equivalent quality of the original CD. The resulting file sizes of Apple Lossless files vary depending upon the original source, since some audio files will compress better than others, but on average they’re usually around 50-70% of the original CD track. Further, since these are lossless formats, they can be used to burn audio CDs, or re-convert to other audio formats in the same way the original audio CD could be—all of the original audio information is present, it’s merely compressed into a smaller file size (in much the same way that a ZIP file works).

So if you’re converting to any higher quality format, whether it’s Apple Lossless or simply a higher bit-rate MP3, you should always re-rip from a lossless source (ie, the original CD), since there’s absolutely no point in doing the conversion otherwise.

For more information and discussion about the various digital audio formats and the relative merits of each, be sure to check out our Digital Audio Formats forum in the iLounge Discussion Forums.

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