Conference cookie::notes$archive:cd_v1

LPs are made with "pre-emphasis" - a kind of equalization - to compensate
somewhat for the uneven frequency response of LPs.  All phono preamps contain
the proper "de-emphasis" circuit to flatten it out.  Of course, CDs don't
need this, but the industry knew that there was a lot of potential CD
material where the only existing copy was a master tape with
pre-emphasis already there, so they built into the CD standard a scheme
where each track on a CD has a flag that says whether RIAA de-emphasis
should be applied, and the player does it if needed.  Some players
even have a light that tells you when this is happening (Technics SLP-2
is one I know of).  Does this help?
					Steve

Hold on there!  My concept of pre-emphisis was totally different:

Pre-emphisis is an equalization promoted primarally by the Japanese.  The
idea is that it improves the S/N ratio for better specs on paper.

If you look at a schematic, there is only a single pole and its not an
RIAA equalizer.

The Meridian Pro displays when it is used (simple matter of picking
out a logic level).  Meridian and others think the pre-emphisized disks
tend to sound worse.

Mark

Wait a second,

Are you saying that the Japanese include these control signals on the disks
they produce (pre-emphasis is turned on by information in the control area
of each frame) so they can better the specs on there players?  What's the
point of turning something on and off if your objective to make it "better".

It seems more logical to me that compensation for something in the music
area makes more sense.
re. 2       

If what you are saying is true then I would assume that German disks do not
have such signals engaged.  Why would any player not needing such "help"
bother to decode the signal if it is not performing any useful function
other to aid the players S/N?

You're gonna have to explain this.  At this point your explanation sounds
a little fishy.  I think we need a little more definitive information on
this particular subject.


- peter

Pre-emphisis is not something turned on and off.  The complete disk is
either equalized with it or not.  It is an equalization, just like record
RIAA equalization, but it only affects the high frequencies.

The point was that it is not the same as RIAA, so CD mastering can not be
done with the RIAA equalized LP master.

At least there were only two standards insead of twice that used on early
LPs.

I still don't understand the point of equalization for a CD.  What is the
point of circuitry which can be cut in and out based on control information
contained in the data frames on the disk.  What is the purpose of putting
the information on the disk in such a fashion that it has to be high freq
equalized to get back the proper signal.  What are they compensating for
- there's no vinyl or oxide fowling up flat frequency response?

peter

Just a guess.     Maybe someone felt there was a potential quantization 
problem at high frequencies that could be solved by boosting the level of
HF info during record and cutting it during playback.  It probably wouldnt
hurt the HF noise figures either.    There must have been enough disagreement
on whatever this was used for, that it became an option and not universally
applied.  Coding it in the disc is the only way to go if you are going to
offer disc producers a choice in something like this.  Wouldnt it be nice
if the various tape formulations and analog noise reduction schemes had a
leadin code system to set up your tape machine ?

Walt

  It could be something to do with the fact that the higher
  frequiencies are attenuated somewhat in the sampling process.
    This is because the higher frequencies are sampled less and
  less upto 20khz untill there are only two samples per cycle.
  In theory if the phases of the sampled and sampling frequencies
  coincide at this frequency you could be sampling on the zero
  crossing points and not see the 20khz freq at all..
  
  
  
  Steve.. 

    There's no such theory. *In theory* if you sample 20 kHz at 44.1
    kHz it doesn't matter. *In theory* even if you sample 20 kHz at
    20.000000000001 kHz it doesn't matter...
    
    Well, the practice may be quite another thing.    :-)
    
    

    
    Could it be that this "pre-emphasis" was like the Dolby-B method
    of noise reduction as applied to analog recordings, and it is existing
    now like a hangover the mornin' after? The Dolby-B process boosted
    recoding levels from about 12KHZ thru 22K along a fairly steep curve
    (the higher the frequency the greater the boost). To obtain a flat
    frequency response when playing back the recording required cutting 
    the high frequency levels (following the same curve), with the
    intended result to attentuate the disk surface noise (actually, this 
    was in the context of tape noise for Dolby, but I would believe it is 
    equally applied to either mastered tapes or retailed pressings).
    
    "Equalization" then is the play-back process that would provide
    flat response from a "pre-emphasized" source. If the CD was generated
    from an "emphasized" analog recording, some method of correcting
    the digitized/emphasized data would be necessary with the CD player.
    
    Obviously the original point of all this is lost on digitally mastered
    CD's....Otherwise, consider that CD players that have this "feature"
    can compensate for shortcomings in the analog-to-CD processes being
    used by some manufacturers.
    
    				DAT: retroengineer
    
    
    

    re .2: I think Mark is right there.
    
    I picked up a copy of HFN & RR at Heathrow last weak, and they had
    an article (if I recall correctly it was a test of the Meridian
    player) where they mentioned pre-emphasis. They even listed a number
    of records they tried that had pre-emphasis enabled (mostly Japanese)
    and others that didn't (mostly non-Japanese).
    
    Now, when I have a little more time, I might type in some selected
    pieces from that magazine... the English havew such a different
    view of things!! We could have some more flaming about capacitors
    and directionality of cables...