digital Filter in CD Player ?

[Doug Ferrell]

Michael,
	Sounds like some NAD engineers did some heuristic filtering alright.  When
you say 0dB, do you mean full-scale swing?  It could easily be the case that
the filter looks for artificial (perfect) edges (like your square wave) and
removes them.  If your levels cause a single bit to vary on every edge, that
would look even more like an "error" to such a filter.
	I know this sounds like sacrilege, but perhaps if you add some very low
level noise (twiddle the LSB randomly), you can fake out the filter.  Or
perhaps round the corners ever so slightly.
	Your standard test signal CD sounds like a great idea.  Are you making
frequency sweeps and other "patterns" as well?

Good luck,
Doug Ferrell

dougf at flashpnt.com


p.s.  I work in digital imaging where similar heuristics cause similar
problems in 2D...  Sometimes "smart" filters are worse than "dumb" ones.


-----Original Message-----
From: owner-synth-diy at node12b53.a2000.nl
[mailto:owner-synth-diy at node12b53.a2000.nl]On Behalf Of Michael
Buchstaller
Sent: Thursday, April 13, 2000 2:17 AM
To: synth-diy at node12b53.a2000.nl
Subject: digital Filter in CD Player ?


Hello Group,

to get some clean test signals for my various amps, i dedided to
create test tones in sound forge on the PC and made CD´s so i could
play them via my CD player without the need to use a computer on
the bench.

Testing with sinuses from 1 HZ to 5 KHz was OK, everything came through
fine. But when i am using square signal, at most frequencies i do not get
any output from the CD player (a NAD 502).
Is there possibly some digital anti-noise-filter that interprets the 0db
Square-
wave as clics and suppresses them ? If yes, is this common practice with
all Cd players, or are there any models that do not tr to filter the output
?

BTW: Of course i could use my modular as a test tone source, but i hate to
calibrate the VCA for a specific frequency; and i find it handy to use a
standard consumer device like a CD player that is available everywhere
as a signal source.


-Michael Buchstaller