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Re: [TCLUG:12423] CD writing software....



On Sat, 22 Jan 2000, Callum Lerwick wrote:

> > PRE-EMPHASIS: If set, the audio has been processed by a pre-emphasis filter,
> >         and the matching de-emphasis filter in the CD player should be
> >         activated.
> 
> Okay, whats that exactly...

I can give you the time constants for the filters if you really want
exact, but I have to go find a book upstairs...

In essence, Pre-emphsis is a simple noise reduction scheme.  By running it
through a boost filter so that the highs are stored at an elevated level,
you "sort-of" get more signal-to-noise coming back out of the
reconstruction filter in the D/A convertor.  But, you have to remember to
de-emphasize.

It actually works pretty well, and if memory serves, you can get a little
better than 16-bit resolution in the upper critical bands of
hearing.  But, it fell by the wayside and is rarely if ever used these
days because of the confusion that arose in it's use; kind of like getting
a cassette and not knowing whether or not to play it back with Dolby or
not.

(The point to note here is that the encoding of the data and the storage
on CD are decorrelated - that's the beauty of digital - so pre-emphasis is
strictly an analog phenom.)

Hope that made a little sense...

Phil M

-- 
Life is complex:
It has real and imaginary components.
                     --Unknown