The Low Fidelity of iPod's Noise... iPod's Noise

Apple (Motto: “Occasionally better, always cooler”) recently announced that the entire EMI catalog of downloadable music would be available at $1.29 a pop, such downloads to be both DRM-free and “offered at higher quality 256 kbps AAC encoding, resulting in audio quality indistinguishable from the original [i.e., CD] recording.” Does a 256 kbps bit rate versus the usual 128 kbps bit rate really provide improved audio quality? Probably not, writes Christopher Beam at Slate, and he’s probably right. The truth is, the audio quality of MP3s played on the average MP3 player, including iPods, sucks. (N.B., I am using "MP3" throughout this post as a generic term to include, e.g., AAC.) But the reason isn’t the bit rate. MP3 sound quality sucks by comparison to CDs because of (1) the compression / decompression (“codec”) programs used to reduce the size of audio files and (2) crappy DACs or digital-to-analog converters. (In fairness, a two year old review in Stereophile says that iPods have "a pretty good DAC.")

The technology behind digital audio of any sort is tremendously sophisticated and the mathematics behind that technology is far beyond my meager math skills. At bottom, however, digital audio takes what is an essentially continuous analog signal (sound waves, themselves a form of mechanical energy converted to a modulated electrical signal by a microphone) and converts that signal to a series of non-continuous or discrete bits, symbolically represented by 1’s and 0’s, by an analog-to-digital converter or ADC. That bit stream is then stored and the stored information is eventually reconverted by a DAC into a continuous electrical signal which is then reconverted by speakers back into sound waves.

By comparison, the earlier analog technology of phonograph recordings involved no analog-to-digital-to-analog processing and, for all its other shortcomings, was therefore considered by audiophiles to be in principle capable of approximating perfect fidelity to the original audio source. To audiophiles, perfect fidelity was (and still is) the Holy Grail of audio equipment – recorded music should sound exactly as though it was being performed live – and in the early days of digital audio technology, a battle raged among audiophiles whether the whole digital audio conversion process constituted a fatal shortcoming. Couldn’t, in effect, the human ear hear the difference between the continuous original source and the “merely sampled” digital signal?

Psychoacoustically, the answer is no. Not, at least, at a sufficiently high sampling rate. Moreover, for anyone possessing a merely so-so stereo in the 1980s, although the first generation of CDs and CD players fell far short of Sony and Phillips' “perfect sound forever” advertising campaign, the sound was indeed significantly better than that from analog LPs. Why? First, because most “so-so” stereos were, in fact, pretty crappy, themselves. Second, because even the best turntables produced at least some unwanted “rumble” noise and tape players produced some unwanted “wow and flutter” noise. Also, LP’s became damaged with every use and, more often than not, rapidly became seriously damaged by scratches and dirt and other causes of “surface noise,” while magnetic tapes suffered their own wear problems. Third, digital technology permitted much greater dynamic headroom. Analog recordings compressed volume because sudden shifts in volume created signal distortion, though in fact that was due more to the limitations of the equipment at that time than the analog process, itself.

Even so, that early generation of CDs sounded crappy when compared to state-of-the-art analog stereo systems. There were various reasons for this, too, not the least of which was the fact that recording engineers simply didn’t have sufficient experience yet with the new technology. But the primary reason CD sound quality has significantly improved since the 1980s is, quite simply, improvement in the ADCs and especially the DACs. Aside from the inherent problems in data compression and decompression, the DACs in most MP3 players isn’t very good. Thus, even when the signal output is fed into a respectable stereo system, as opposed to those crappy little earphones, the sound still doesn’t measure up to a CD played on a decent CD player through the same system.

No sound recording technology or equipment is better than its weakest link. I own an iPod, and I enjoy it. But MP3 players are for convenience, just as even the best car stereos are. What they’re not for is audio quality, not if quality means anything within a country mile of high-fidelity, anyway. If an extra 30 cents a tune is worth it to you to be able to avoid DRM restrictions, go for it. If you're seeking audio quality though, forget it. Especially if you're only going to listen on those tiny earphones or a pair of only marginally better computer speakers. Keep buying the 99 cent versions and save up for a decent stereo and the CDs, instead.