Blog logo, you're not missing much
AudioAcoustics

Serving the Acoustics Community Since 1994

Cross-Spectrum Acoustics Inc. offers Sound & Vibration Consulting Services

September
Sun Mon Tue Wed Thu Fri Sat
  6
       









Sep 06, 2003

Chris Menge of HMMH is in the news for suggesting a noise limit for a race track.

Philip Greenspun has an interesting article on his blog about the death of the compact disc. Philip is a smart guy, and I agree with this general thesis, but some of his statements are a bit misleading. For example, he states:

The encoding system is so badly designed that 80 percent of the bits in the disk’s data stream carry no information, which is one reason that MP3 compression is so successful.

That’s not exactly true - if it were, one wouldn’t be able to hear the difference between an mp3 and uncompressed audio, and yet many people can (now whether most people care about the difference is another question).

He goes on to state:

They forgot to allocate a few bytes for the name of the album or the titles of the tracks on the disk so you have a medium that stores 700 megabytes but not the critical text information that you’d want to see (if, for example, you loaded your CDs into a jukebox).

The original Red Book standard did not allow for such information, but the CD Text feature that was appended to the Red Book standard in 1996 does allow for this. So in other words, the CD format does allow for this, but the record and consumer electronics companies haven’t bothered to support it.

Finally he states:

CDs are so badly engineered that they actually have more distortion than the LP records that they supplanted, especially for classical music (the CD is at its least accurate for very quiet sounds but works great for Heavy Metal). Most serious audiophiles listen to analog LPs or the new DVD-Audio and Super Audio CD (SACD) formats.

Again, this has to do more with CD production then with CD capabilities. CD’s have a 96 dB dynamic range, and most CD-players have 90+ dB of signal-to-noise ratio, compared with ~60 dB dynamic range and ~60 dB signal-to-noise ration for analog LP’s. While CD’s may have problems with recording levels set near the least-significant-bit (which can be partially overcome through dithering), a quiet passage for a CD can be recorded at -70 dBfs which gives plenty of room to adequately capture quiet sounds and still exceed the dynamic range of a typical LP. Of course we still have the problem that many CD’s just aren’t properly mastered.

Philip’s overall point is that the record companies screw everyone, and I agree. However, if the CD is dying, it’s not necessarily because of shortcomings in the format itself - the blame lies in part on the producers that have refused to take full advantage of all the capabilities the CD format offers. Future formats such as SACD and DVD-Audio have the potential so address the shortcomings of the compact disc. But producers and engineers need to do their part to utilize these new formats. Otherwise, garbage in = garbage out, and we’re back to the status quo


permanent link