digital Filter in CD Player ?

[Martin Czech]

The idea with the CD player as such is very good. If you take a cheap
portable chassis (like me) you have a very pure sine wave (and other)
source that would not be affordable otherwise. Everything below 0.1%
THD is not so cheap. With stereo files you can even have different
frequencies at the same time for inter modulation measurements.

How do you guys synthesize signals with frequency components higher then
Fs/2 ??

You can do this with cheap software like cool edit, and you can hear how the
harmonics fold back...

I mean doing a sine wave < Fs/2 is easy, but waves with harmonics require
quite sophisticated interpolation to sound right.

Better start with a set of odd sine waves.  Then you are sure to
be band limited.

CD-Audio has no good error detection/correction (compared to CD-ROM).
The rest is done via interpolation. As Dan said, if strange signals come
out of the ERC layer, these are believed to be wrong and interpolated.
Perhaps a not so good chassis will play them. Perhaps this part of the
software is proprietary, i.e. differs from manufacturer to manufacturer.


I really recommend to store audio masters not only on CD-AUDIO but also
on CD-ROM (e.g. .wav format), even if this implies additional effort
due to limited space on CD-ROM (i.e. you may need two CD-ROM for one
CD-Audio). Copying audio material from CD-Audio is not such a good idea.



m.c.

:::From: "Dan Gendreau" <gendreau at rochester.rr.com>
:::To: <buchi at takeonetech.de>, "synthDIY" <synth-diy at node12b53.a2000.nl>
:::Subject: RE: digital Filter in CD Player ?
:::Date: Thu, 13 Apr 2000 11:52:16 -0400
:::Content-Transfer-Encoding: 7bit
:::Importance: Normal
:::
:::> 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 ?
:::
:::Thats probably it.
:::Certain waveforms can actually damage your speakers, so the cdrom drive
:::probably doesnt allow drasic slew rates like that.
:::
:::Try low pass filtering them at like 22kHz. Your CD player cant produce
:::frequencies beyond 22kHz anyway because the DAC output is analog filtered to
:::remove harmonics above that.
:::
:::-Dan Gendreau