PC Magazine Labs recently conducted listening tests to help you make the right tradeoffs between file size and audio quality. With some basic understanding of digital audio, you can decide what encoding rate best suits the particular music you want to ripâ€"MP3 jargon for encoding files. The goal is to maximize the number of songs you can store in your MP3 player with minimal compromises in music quality.
MP3 compresses near-CD-quality music to one-twelfth the size of the original CD audio data, but MP3 players come with a finite amount of memoryâ€"either 32MB or 64MB. MP3 music can be encoded at various bit rates. Generally, the higher the bit rate, the better the audio quality and the larger the file size.
MP3 is a "lossy" compression schemeâ€"meaning some quality is lost during compression. But MP3 achieves perceptually "lossless" compression through psychoacoustics. The compression technique cuts out all the audio information that we can't perceive or that isn't needed.
Dynamic range and sample rate are the two major factors that affect the quality of digital audio. As you lower the bit rate, you give up one or a little of both. A good dynamic range is required to reproduce faint sounds accurately and not clip the loud parts. A high sample rate enables the accurate reproduction of the original recording across a wide range of instruments.
Based on our listening tests, we found that a 128-Kbps MP3 clip (sampled at 44.1 kHz) is almost impossible to distinguish from the music on CD. This is the bit rate you should use for classical music. If you prefer pop or contemporary vocals without high-pitched instruments, then the 64-Kbps encoding (typically sampled at 22.05kHz) is likely to be just as good at preserving the dynamic range. And the lower bit rate produces files that are half the size.
As an alternative to MP3, Microsoft's Windows Media Format (WMF) 4.0 is designed to store twice as much music as MP3. Most players will soon support WMF, which can encode at 64 Kbps with the full 44.1-kHz sampling rate in stereo. 128-Kbps MP3 files are typically encoded at 44 kHz stereo. They can also be encoded at 64 Kbps, but most MP3 encoders sample at 22.05 kHz, limiting the frequency range to 11 kHz. We found that Microsoft's proprietary algorithms produce near-CD-quality music files at 64 Kbps, compared with the 128 Kbps required by MP3 for such quality.
To test Microsoft's claim that its 64-Kbps encoding is a better way to go, we encoded three types of music (rock, jazz, and classical) with MP3 at 128 Kbps stereo and WMF at 64 Kbps stereo (at 44.1-kHz sampling rates). Only WMF-encoded jazz (with a lot of cymbals) produced annoying artifacts. For the other clips, we found it difficult to distinguish the MP3- and WMF- encoded files from the originals.
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