From: winalski@adserv.enet.dec.com (Paul S. Winalski)
Subject: Re: DAT, DCC and MD
Reply-To: winalski@adserv.enet.dec.com (Paul S. Winalski)
Organization: Digital Equipment Corporation, Nashua NH
Date: Fri, 22 Jan 1993 02:37:25 GMT


In article <GLAS.93Jan21081603@muresh.et.tudelft.nl>,
glas@muresh.et.tudelft.nl (Jack Glas) writes:
|>
|>To do something about the disadvantages mentioned above Philips (one 'l')
|>invented the 
|>Digital Compact Cassette system. These players doesn't have rotating heads
|>(so they can
|>become cheaper than DAT recorders), and you can play (and record) you normal
|>Compact 
|>Cassettes in them. The system makes use of PASC (precision adaptive subband
|>coding) to 
|>compress data. 

You CANNOT record normal cassettes on a DCC deck!  You can only play them back.
If you want to both play and record analog cassettes, you still need an analog
cassette deck.  So DCC doesn't save you anything on the number of components
in your stereo system (if you wish to retain the capability to record analog
cassettes).

As for rotating head systems being less expensive than static head systems, that
doesn't seem to be the case.  The mechanism for static-head DAT (SDAT, such as
DCC) is in principle simpler than rotating-head DAT (RDAT, such as the Sony
DAT system we call "DAT"), but in practice other considerations occur.  RDAT
can cram a lot more information onto the same amount of tape than SDAT, which
is why RDAT doesn't need data compression and SDAT systems such as DCC do.  To
use the same tape form factor as analog cassettes and still get a reasonable
amount of music on the tape, DCC has had to use thin-film head technology.
Also, SDAT has more stringent tape registration and calibration tolerances.
Manufacturing to those tolerances drives up the price of SDAT.

To see how expensive RDAT could be if manufactured in mass quantity, just
look at the price for VCRs (which use essentially the same technology).

The current crop of DCC decks is more expensive than the current crop of DAT
decks by several hundred dollars.

|>PASC is based on two phenomena of the human ear:
|>* One can only hear sound above a certain level, called the absolute hearing
|>threshold.
|>* Loud sounds hide, or mask, softer sounds in their vicinity. They dynamially
|> adapt the
|>  hearing threshold. This applies to the frequency domain (spectral masking)
|>as well as to 
|>  the tiem domain (temporal masking).
|>So you have to be a GOD to hear the differences between CD and DCC.

That is the theory, anyway.  In practice, it's not that simple.  I have heard
reports from several mere mortals who can hear differences between DCC and CD.
They are subtle differences, admittedly, ulikely to bother the non-critical
listener, but they are there.  PASC is like other compression systems:  it's OK
for most everything, but there are "tricky" passages of music that it can't
handle.

|>I think everyone who doesn't believe me (which ofcourse is also a matter of
|>taste) should
|>at least read one of the following articles:
|>* Gerard C.P. Lokhoff: 'dcc-Digital Compact Cassette', IEEE transactions on
|>consumer 
|>	electronics, Vol. CE-37, no. 3, pp 702-706, august 1991.
|>* Gerard C.P. Lokhoff: 'Precision adaptive subband coding (PASC) for the
|>digital compact
|>	cassette (DCC)', IEEE transactions on consumer electronics, Vol. CE-38,
|> no. 4,
|>	pp 784-789, november 1992.

I don't need to read Philips propaganda, thank you.

--PSW