CDs are often claimed to perfectly reproduce
music. But in an editorial on August 22 about the dangers
of "Digitalized History," the New York Times
asserted "even in the best digital recordings of live
performances, there is a loss of grain, of substance."
Is the Times correct?
Yes, the New York Times is correct in the case of all
digital sound, including CDS, DVDs, DVD-Audio, Theatrical
movies which use digital equalizers, digital tape decks,
TV and MP3s, which use Pulse Code Modulation (PCM).
In recording sound, the PCM operating system uses a
brick-wall filter to cut out all information above 20
kHz. This truncation has two deleterious effects on
music: First, it destroys the harmonics by removing
the information above 20 kHz, which, though inaudible
to the human ear, provide part of the chain reaction
that give music its sound. Second, the filter itself,
in vibrating introducing some spurious information in
the audible range. The remaining information, after
being converted to a digital bit stream, is then "quanticized"
into 16-bit words. Such quanticization requires further
filtering and rounding off. If there are even minute
fluctuations in the current, it results in conversion
errors. On playback, the PCM process is reversed, but
the missing information --including information above
20khz— can not be restored, no matter how sophisticated
(or expensive) the digital to analog electronics. It
is not "lossless" compression. In a PCM replication,
a truncated part must stand for the whole music. The
only exception in digital sound is SuperAudio (SACD),
which uses a different operating system, called Direct
stream Digital. Direct stream Digital, unlike PCM, does
not chop out the bandwidth above 20 kHz or filter the
digit information into multi-bit words. Even this exception
applies only if there is no PCM equipment, such as digital
equalizers, used in the recording and playback process.