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About MP3 custom import options |
The custom import options in the Preferences window give you increased control over the quality of the music conversion and the amount of disk space the songs use.
Bit Rate: The higher the Mono or Stereo kilobytes per second (kbps), the higher the audio quality and the larger the file size. The most common bit rate for stereo MP3 files is 128 kbps. Lower bit rates are more appropriate for sound files containing voice recordings (as opposed to music).
Variable Bit Rate Encoding (VBR): This setting varies the number of bits used to store the music depending on the complexity of the music. This can help keep file size to a minimum.
Channels: Mono files are about half the size of stereo files. Mono is appropriate if you'll be listening to your MP3 files using your computer's built-in speaker. If you'll be listening to your MP3 files using your stereo system, use Stereo or Auto. Auto converts tracks that are already monaural into mono MP3 files, and stereo files into stereo MP3 files.
Stereo Mode: In Normal mode, your MP3 files contain one track for the right and one track for the left stereo channel. In many cases, the two channels contain related information. Joint Stereo allows one channel to carry the information that's identical on both channels, while the other channel carries the unique information. At bit rates of 128 kbps and below, this can improve the sound qualty of your converted audio.
Smart Encoding Adjustments: iTunes can analyze your encoding settings and music source to greatly improve the quality of your encoded files. When Smart Encoding Adjustments is selected, iTunes changes your settings as needed to maximize the sound quality.
Filter Frequencies Below 10 Hz: Filtering inaudible frequencies results in smaller, more efficient files without any perceived loss in audio quality.
Sample Rate: Sample rate is the number of times per minute that the music waveforms are captured digitally. The higher the sample rate, the higher the quality and the larger the file size. Be sure to choose an encoding rate that is no higher than the rate used to originally store the music, or you'll waste space. CD quality, for example, is 44.100 kHz, so choosing a higher rate when you're encoding from a CD is unnecessary. In general, the best choice is Auto, which uses the same rate as the original music.