Digital formats

Robert Shearer (shearer@usf.teradyne.com)
Fri, 5 Jun 1998 16:33:37 -0400 (EDT)

This discussion about digital recording formats, and one being better
than the other, is interesting to me as an engineer who studied data
acquisition
as part of my undergraduate work.
Lest anyone forget: digital recording is not a true recording, but a
very good approximation. For it to work, it takes advantage of the fact that
the human hear has a frequency range that tops out at 20KHz (and even that is
really higher than most people can really hear).
When a digitally recording is reproduced (translated to analog) the
playback introduces all kinds of harmonics and noise that was not part of the
original recording. What the playback mechanism must do is condition the
resultant signal to remove/reduce the synthesized noise. (I haven't confirmed
this personally, but have been told that the conditioning circuitry is what
drives the cost of high-performance digital audio equipment).

Thus, when you talk about one format having an advantage over the
other,
the most critical component is how well the *playback* recreates the signal.
It is quite likely that there are minidisc *players* that have superior
filtering and conditioning to DAT players. Before you can make a true
comparison,
you have to first ensure that the playback equipment is equivalent...which is
extremely difficult to do, BTW. (In the world of signal analysis, "harmonic
distortion" is considered to be a great way to use impressive numbers to say
nothing significant).

Touching on something Alan said about the no moving parts recorder:
having sold our souls for digital technology, we still cheat ourselves using
primitive electromechnical forms of playback/recording. As the density of solid
state microelectronics becomes higher, while the price drops through the floor,
we should see within the next decade recordings-on-a-chip. Imagine having
today's CD-quality or better in a player on your wristwatch!

-Robert Shearer