And so it came to pass, on 08-07-96 23:14,
   that Herry Budiutama spake unto All :
 HB> I need to know the difference between
 HB>         1.  Dolby B
In essence, boosts the high end going to tape, and reduces it (and hiss along 
with it) on playback.  It's a little more complicated that simply EQing it 
(for example, the EQ cutoff point varies somewhat depending on signal 
content), but that's the gist of how it works.
 HB>          2.  Dolby C
Similar concept to dbx - the dynamic range of the signal is compressed going 
to tape, and expanded again on playback.  This is somewhat over-simplified, 
(Dolby C operates on multiple frequency bands, which dbx effects the signal 
equally across the entire spectrum), but again, it gives you a basic idea of 
what it does.
 HB>          3.  Dolby HX Pro
HX stands for Headroom Extension.  It operates only during recording; the 
record bias is adjusted automatically depending on the signal content.  If 
there's a lot of high-frequency energy in the signal, the bias is reduced to 
avoid saturating the tape, to improve headroom.'
 HB>       4.  Dolby Pro-Logic
Simply a method of encoding multiple audio channels into a recording.  Used 
for movies, videos and such, which can use separate main stereo, center 
(diialog), surround, and in some cases, subwoofer channels.
 HB> How exactly does Dolby NR reduce noise on the tape?   
Varies depending on which version of Dolby NR you're using.  See above.  On 
the professional level, there's also Dolby S (*very* high-end pro stuff) and 
SR (found on some entry-level pro gear) noise reduction.
 HB> By ear, it seems that I can achieve the same result through a
 HB> graphic equalizer.  
Yes and no.  See above.
 HB> Is the sound compromised in any way when NR is on?
Theoretically, no.  In reality, many real-world factors come into play that 
can affect NR's effectiveness.  This alone is an extensive subject that 
wouldn't mean much without a much more extensive explanation of exactly how 
the different types of NR work.
 HB> On another note, will a more precise rotation of music CD result in
 HB> a richer deeper sound?   
Hardly.  It may improve error detection/correction, but that won't affect the 
"richness" or "depth" of the sound, as you're simply reading ones and zeros 
off the disc.
 HB> Some companies are selling these rings that you put around your CDs
 HB> (which will increase the moment of inertia).
95% chance they won't make the slightest bit of difference to your sound.  
 HB> One claims that a more precise rotation will result in a deeper
 HB> bass and less need for error correction (which implies that the
 HB> everyday CD player doesn't rotate the disc accurately).  
It should theoretically improve error handling to have the disc rotation as 
stable as possible, but I don't see how they can claim it will provide a 
"deeper" sound...
 HB> Another claims that normally, without the rings, the laser reader
 HB> from the player actually reflects off the sides of the CD and
 HB> interferes with the reader. With the rings, these reflections are
 HB> reduced and hence, you'll hear better music.
Horsehockey.  This goes back to the ongoing, infamous Green Marker debate 
(proponents claim that simply coloring the edges of the disc with a green 
Sharpie will improve sound, since the green absorbs stray red laser light... 
hahahaha).
 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 data bits are the same size throughout the disc.  Since the linear 
velocity of the disc increases as you move toward the outer edge (to 
understand this, imagine standing on a merry-go-round -- you feel the air 
moving past you faster if you stand on the outer edge, than you do if you 
stand in the middle), the disc's rotational speed (angular velocity) is 
decreased as the pickup moves from the center to the outer edge of the disc.  
This means the lands and pits (bumps and dents in the disc's surface that 
reflect or scatter the light) are always moving past the laser at the same 
speed.
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Q: Why don't blind people skydive?
A: It scares the heck outta their dogs!
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