En teknisk diskusjon om pre/de-emphqasis:
http://www.dsprelated.com/showmessage/2587/1.php
"Randy Yates wrote:
> What is it?
Emphasis / De-Emphasis a complementeray cut-and-boost pair of
high-shelve filters used before the ADC stage and after the DAC stage
(ie. the producer of the CD applies emphasis to the analogue signal, and
the CD player then has to apply de-emphasis). The transition band is
specified by the 50/15 rule (50us and 15us timing constants for the
corner frequencies), the gain is about 10 dB (specs should be available
on the net).
> Why is it used?
If you assume that high frequency content of music is low in average
(decreases with -6dB/oct for example), then boosting the high
frequencies would increase the SNR in that range without affecting the
average SNR in the low frequencies too much.
> How is it usually implemented (digitally or analogically)?
Obviously, it should be implemented in the analogue domain. However, if
you convert an AES/EBU digital audio stream to some other format (for
example raw data, as Rune likes to
, you should theoretically check
the emphasis bit, and apply a digital de-emphasis if necessary. I once
converted the analogue filter specs to digital filter (sorry, don't have
the files handy, as I'm not at work). There has been plenty of talk on
how to do this best here in comp.dsp, it is slightly non-trivial because
bi-linear transform introduces too much warping.
However, I don't think there are many CDs that actually use emphasis, so
it's a pretty academic subject.
Regards,
Andor
"