| The factory settings that iTunes uses for importing music are perfectly fine for most music lovers and listening scenarios. So if you'd rather explore some of the more musical and less technical aspects of iTunes, feel free to skip to page 30. But if you're an audiophile or are just curious, read on for a look at how audio compression works and at how you can adjust the way iTunes applies it. CD-quality stereo sound requires about 10MB of disk space per minute. By using compression, iTunes can lower audio's appetite for storage by a factor of 10 or more. Most audio-compression schemes use something called perceptual encoding, which eliminates those portions of an audio signal that our ears don't hear well anyway. Because some information is lost in the process, this form of compression is called lossy. iTunes supports two lossy compression schemes: MP3, the format that helped fuel the Internet music revolution; and a newer method called AAC (short for Advanced Audio Coding). Each scheme has advantages and drawbacks. iTunes also offers a lossless compression scheme called Apple Lossless encoding. It doesn't provide nearly as much compression as MP3 or AACfiles are only about half the size of the original. But true to its name, Apple Lossless imposes no quality loss. If you're a golden-eared audiophile with plenty of hard-drive space, you might prefer to rip your CDs using the Apple Lossless encoder. Changing Importing Settings From the factory, iTunes is set up to encode in AAC format. By adjusting the Importing options in the Preferences dialog box, you can change the encoding settings to arrive at your own ideal balance between sound quality, storage requirements, and listening plans. Step 1. | Choose Preferences from the iTunes menu.
| Step 2. | Click the Advanced button.
| Step 3. | In the Advanced preferences area, click the Importing button.
Encoder Options at a Glance |
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Encoder | Comments |
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AAC | Best balance between sound quality and small file size. | MP3 | Not as efficient as AAC, but broadly compatible with non-Apple portable players and computer systems. | Apple Lossless | Creates much larger files than the MP3 or AAC encoders, but with no audio quality loss. Files won't play on iPod shuffle or older iPods. | WAV and AIFF | Create uncompressed files that use 10MB of disk space per minute. (AIFF, which stands for Audio Interchange File Format, is a standard audio format on the Mac; WAV is its equivalent on Windows. Both formats are broadly supported on Macs and Windows computers.) |
| | | Step 4. | Adjust importing settings as shown below.
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AAC: More Bang for the Byte You want the storage efficiency that a lossy encoder provides. Should you rip your CDs using the AAC encoder or the MP3 encoder? If you'll always use iTunes, an iPod, and the other iLife programs to play music, by all means use AACI do. But if you anticipate transferring tunes between computers or non-Apple portable players, use MP3. Here's why. Audio compression is measured in terms of bit rate, the average number of bits required for one second of sound. To obtain near CD-quality audio, MP3 requires a bit rate in the range of 128 to 192 kilobits per second (kbps). Higher bit rates mean less compression and better sound quality. AAC is more efficient than MP3it does a smarter job of encoding music, which means you can use lower bit rates and still get great sound quality. Audiophiles love to argue the fine points, but to most ears, a 128 kbps AAC file sounds at least as good as an MP3 file encoded at 160 kbps. What does this mean to you? If you use AAC when importing CDs, you'll use disk space more efficiently. This can help you shoehorn a mammoth music library onto an iPod. The downside to AAC? Your music files will be less compatible with other music software and hardware. MP3 is supported by every music program, personal computer, and portable music player; AAC isn't. There's one more reason you might consider using MP3 instead of AAC. If you plan to burn CDs in MP3 format as described on page 60, you should rip your music in MP3 format. Any Mac with version 6.4 or later of QuickTime can play AAC audio. For best compatibility with all of the iLife '06 programs, use QuickTime 7.0.4 or a later version, if available. You can also play AAC audio on a Windows computer after installing QuickTime for Windows, which is included with iTunes for Windows. One more thing. As page 30 describes, the iTunes Music Store delivers its tracks in AAC format. The AAC music you buy contains some copying restrictions. But AAC files that you rip from your own CDs contain no such restrictions. |
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