When you rip to a lossy format, however, if you convert the file later to another format, you lose some of its quality. This is similar to the way a photocopy of a photocopy doesn’t look as good as the original.
Some people prefer lossless formats because they reproduce audio as it is on CDs. Lossy compression is a compromise, used to save space, allowing you to store more music on a portable device or hard disk, and making it faster to download. However, most people can’t tell the difference between a CD and a lossy file at a high bit rate, so if you’re ripping your music to sync to an iPhone, lossless files are overkill.
Lossless rips are a good way to make archival copies of your files, since you can convert them to other formats with no loss in quality. And you can have iTunes convert them automatically to AAC files when you sync.
The best way to judge the quality of an audio file—relative to its original, not to its musical or engineering quality—is to look at its bit rate. Audio file bit rates are measured in thousands of bits per second, or kbps. I mentioned above that a CD contains audio at 1,411 kbps, and when you convert that audio to a lossy file, its bit rate is much lower.
A higher bit rate is better, so a 256 kbps MP3 or AAC file is better than a 128 kbps file. However, with lossless files, this isn’t true. The bit rate of a lossless file depends on the density and the volume of its music. Two tracks on the same album, ripped to a lossless format, may have bit rates of, say, 400 kbps and 900 kbps, yet when played back, they both reproduce the original audio from CD at the same level of quality. Lossless compression uses as many bits as needed, and no more.
Here are two albums I converted to Apple Lossless. You can see the bit rates vary from 353 kbps to 845 kbps. The first album is a chamber ensemble, and the second solo piano. The complexity and volume of the music affect the final bit rate needed for lossless compression. (Click to expand).
If you’re ripping music to a lossy format, it’s good to choose the iTunes default of 256 kbps, unless you need to cram a lot of music onto your portable devices. If you’re ripping audiobooks or other spoken word recordings, you can use much lower bit rates, since the range of the human voice is quite narrow. Audiobooks are often ripped at 32 kbps, and they sound fine.
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