Is There A Real Difference Between MP3s and CD-Quality Sound?

by Justin Thomas •

Sound Spectrum Graph: MP3 vs CD Quality

Since their appearance on the internet in 1994, MP3 files have made music much easier to transfer around the world. Because MP3 files are compressed, their file size is typically ten times smaller than the original, uncompressed audio file. This means quicker downloads, and the ability to store more music on an iPod.

However, because MP3 files are compressed, the sound they produce is always going to be inferior to CD-quality sound. But does this really manner? Is there a meaningful difference between a MP3 audio file encoded at 320kbp, and a lossless (CD-quality) sound? In many listening situations, MP3 files will pass the test with most listeners. But if you are listening on high fidelity equipment, you may notice some sound artifacts, because some parts of the music are actually missing.

To understand this, let’s examine what’s actually involved in making a MP3 file. The MP3 coder splits a music waveform into discrete time chunks. Then, using Transform analysis, examines the spectral content of each chunk. Assumptions are made by the codec’s designers, on the basis of psychoacoustic theory, about what information can be safely discarded. Quiet sounds with a similar spectrum to loud sounds in the same time window are discarded, as are quiet sounds that are immediately followed or preceded by loud sounds. Other compression techniques are also used.

In an article in Stereophile magazine, John Atkinson explains that all MP3 codecs permanently discard real musical information that would have been audible to some listeners when played through some systems. After much spectral analysis, the author John Atkinson concludes:

Basically, if you want true CD quality from the files on your iPod or music server, you must use WAV or AIF encoding or FLAC, ALC, or WMA Lossless. Both MP3 and AAC introduce fairly large changes in the measured spectra, even at the highest rate of 320kbps. There seems little point in spending large sums of money on superbly specified audio equipment if you are going to play sonically compromised, lossy-compressed music on it.

Gizmodo also did a listening test with a 1000 volunteers, to discover which MP3 bit rates were acceptable to their ears. Almost all the listeners were happy with MP3 files encoded at 200 kbps and above.

When music is encoded at rates below 192kpbs, many listeners hear a distracting phasing effect on high-frequency sounds like those produced by cymbals.

So, after surveying many online articles and forums, and after doing my own audio tests, I’ve come to this conclusion:

In most listening situations, music played in MP3 files encoded at 256kpbs or higher, is virtually indistinguishable from the same music played in lossless formats like FLAC or WAV.

However, if you listening on a audiophile-grade sound system, you may be able to detect some definite sound quality issues when listening to MP3s. This is especially true when listening to classical music, or other music that covers the full dynamic audio range.

If you are listening on a iPod or MP3 player, you can probably stick with MP3 files, because the circuitry in iPods and other MP3 players is too small to properly drive good headphones. If, however, you are using a portable headphone amplifier in combination with high fidelity headphones, you may want to opt for a lossless audio format.

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