-=> Quoting Herry Budiutama to All <=-
 HB> I need to know the difference between
 HB> 1.  Dolby B
Gives 10dB noise reduction above 3Khz on a sliding scale upwards.
 HB> 2.  Dolby C
Gives 20dB noise reduction more or less broad band.  (this is an
approximation)  Above a certain threshold compression and exansion take
place that doesn't take place in B type Dolby to add to the headroom and
cut down on saturation of the tape at higher recording levels.
The above two systems ABSOLUTLY REQUIRE that the tape be accuratly
calibrated to the machine in question to prevent losses during
record/playback.  Levels & EQ both must be precise.
 HB> 3.  Dolby HX Pro
Dynamically alters the AC bias applied to the record head during
recording to compensate for higher audio frequencies acting as "bias"
for lower frequencies.  Also dramatically improves headroom at higher
record levels.
 HB> 4.  Dolby Pro-Logic
Multi channel usage for movies etc.  Someone else could probably expound
on this better. :-)
 HB> How exactly does Dolby NR reduce noise on the tape?   By ear, it seems
 HB> that I can achieve the same result through a graphic equalizer.  Is
 HB> the sound compromised in any way when NR is on?
Dolby dynamically alters the frequency response and level during record
to boost low-level sounds.  A complementry cut back takes place during
play.  Hence the noise goes down with it.
 HB> On another note, will a more precise rotation of music CD result in a
 HB> richer deeper sound?   Some companies are selling these rings that you
 HB> put around your CDs (which will increase the moment of inertia).
Nice thought. :-)  There is methods in the CD decoding to deal with
minor rotational problems.
 HB> Does the CD rotate at different speeds as the laser reader moves
 HB> toward the outer disc?  Is there more data in the outer rim than
 HB> the inner rim?
The CD rotates at roughly 500 rpm at the start as it is read from centre
to outside edge.  At the outer diameters, the speed is 200 rpm.  This is
done to ensure the data that comes off the disc is at the proper rate.
Portable CD Players with the memory feature tend to double this rotation
speed and plow the cd music into a memory so the memory contents can be
"played" during bumps etc.
Hope the above is of assistance.
See ya, Cameron Hall
cameron.hall@bluebeam.gryn.org | ad121@freenet.hamilton.on.ca
Blue Beam BBS | 905 662 5784 | Stoney Creek Ontario Canada | v34 vFC FAX
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