response 12 of 65:

Mar 19 20:28 UTC 2002

I haven't got time to do this justice...  I will have to come back 
and write more later.   

Dolby and dbx Noise Reduction both work by compressing parts of the 
signal on recording and expanding them on playback.  When the signal is
expanded on playback, the volume of the tape hiss, relative 
to the signal, is reduced.   The systems differ in their choice 
of what to compress.

dbx is a straight 2:1 - 1:2 dynamic range compression 
scheme.  This system was very effective 
at nearly elminating tape hiss, but it was so 
aggressive that it sometimes introduced some audible modulation 
of the tape hiss, which was called "pumping" or "breathing."
It was pretty much agreed by everyone that dbx tapes were 
intolerable to listen to on machines which did not have dbx 
decoding.  I never worked with dbx equipment.

In the Dolby techniques, the amount of compression done to 
the signal varies with the audio frequency.  The higher
the frequency -- the more likely the signal is to get lost in tape 
hiss -- the more compression is done.   This is not as effective
as dbx, but it also means that a Dolby-encoded tape can be played
back without decoding, and most people won't object too much to the
resulting sound -- it's a little "bright" because the high frequencies
have been boosted.   This is considerably more complicated than dbx
and to work best, it requires that the tape deck be properly tuned
to the tape being used.

    Dolby A is a professional noise reduction system.  You will not find
    it in home audio equipment.
 
    Dolby B was the first Dolby noise reduction product for home use.
    Any cassette deck you find with a switch marked just "Dolby" 
    is controlling "Dolby B" circuitry.  Dolby B was introduced maybe
    around 1973, for a guess without looking it up. 
    Dolby B gets about 10db of tape hiss reduction -- much less 
    than dbx, but the tapes sound OK if played on equipment without Dolby.

    Dolby C was the second home version, introduced maybe around 1979.
    In a perfectly working system it got 10dB more tape hiss reduction,
    but because it was such an aggressive system it was more audible 
    when there were small tape/machine equalization problems,
    and Dolby C tapes sounded somewhat shrill when played without 
    decoding. 
  
    Dolby S came out after I had stopped paying attention to 
    cassette technology.


Tape selector switches of EX, SX, and ZX tell me you've got your hands
on a Nakamichi brand tape deck, because those were Nakamichi's 
own names for the tape formats.  Some Nakamichi models in good 
working order are quite collectible, selling for hundreds of 
dollars.  Nakamichi was usually regarded as the premier manufacturer
of cassette decks from the early 1970s into the CD era.
However, because Nakamichi and the rest of the world disagreed on 
how equalization was to be done, tapes recorded on Nakamichi machines
sound "dull" on other manufacturer's machines.  I have considerable
experience with this; I lived with or owned three Nakamichi recorders
back in the cassette era.

Tape formulations: roughly equivalent, on each line:
 
 Type I = Normal = Ferric = EX
 Type II = Chrome or Chrome-Equivalent = CrO2 = SX
 Type III = Ferro-Chrome = FeCrO2   <-- this formulation failed in the market
 Type IV = Metal = ZX
           Type IV / Metal tapes can be played back correctly with a 
           switch in the Type II/Chrome position, but they cannot be 
           so recorded.

Actually *explaining* them will have to wait.

response 14 of 65:

Mar 19 21:46 UTC 2002

We have a Kenwood with Bias Preset and Auto Bias that apparently detects the
tape type as that is not a choice. Yes it was Nakamichi with the EX SX ZX.
We have about 20 tape decks, some of which work.  CrO2 is sometimes just
labelled 'high' - high bias?  Some tapes are labelled 120 (I, normal?) and
some 70 (II, IV?) - is this bias or equiv?

We will skip dbx since only one deck has that and take your advice to use
Dolby (B) rather than C.  Don't have any S.  Jim likes to hear things brighter
- perhaps his hearing is shot from too much hammering, but he turns on Dolby
during play for tapes not recorded with it.  

One deck has settings Normal (120 msec), FeCR (70), CrO2 (70) and Metal (70).
Is the FeCr same as FeCrO2 that you mentioned as type III?  Some decks require
you to set both bias and equ and various combinations work for I, II and IV.
For instance both buttons out for I, both in for IV, one in and one out for
II.  A couple of these decks are not understandable.  

If you are interested, Ken, you are welcome to come over and admire and even
play with our tape deck collection.  We are still trying to fix one good one
to the point where it:  plays, records (both channels), and the door works.
We are replacing belts, tires, motors, springs and other bits and pieces.

Were home tape decks first popular around 1973, or even earlier (without
Dolby)?

We have encountered a variety of autoreverse mechanisms.  Usually the head
and tape stay put and the spindles/rollers switch direction, either by some
system of gears, or by acctually reversing motor direction (would this be by
changing polarity to a DC motor?).  One deck swivels the play head, and we
ran across one that actually turned the tape over for you, a very early model.
MCM electronics sells new autoreverse play heads for $2, or the swivelling
type for slightly more (also IEEE printer cables for about $2-3, of the type
that our friend paid $25 for recently).

response 16 of 65:

Mar 20 17:58 UTC 2002

Hoo boy.  I can't explain Dolby HX Pro without covering "bias."
And I'm not even sure I can explain that very well; I may go out
and look for a URL to point you to.
 
In brief:  Dolby HX Pro is not a noise reduction system at all.
"HX" stands for Headroom Extension; it is a circuit to reduce
the bias current a bit when there is lots of high frequency
energy present in the musical signal, to try and stop too much total
high-frequency signal from going into the record heads.  Dolby HX Pro 
is only applied in the recording process; no decoding playback 
is required.

My last high-quality cassette deck had HX Pro, but I eventually 
concluded it didn't help the sound and I turned it off.

response 18 of 65:

Mar 21 17:25 UTC 2002

The marketing for HX Pro argued that when too much high-energy signal
went into the record heads or tape that there was some "self-erasing"
going on, resulting in less-than-optimal high frequency performance.
So that's why it was called "HX Pro," for Headroom Extension.
Once the system accomplished its goal of getting a hotter high-frequency
signal onto the tape, there is no need for any special processing 
to play it back.
 
You know, the more I write this stuff, the more I remember why
I'm recording stuff digitally these days...

response 20 of 65:

Mar 22 23:11 UTC 2002

        I still have an outboard Dolby box.  Control knobs on it 
to control things.  Came with a reel to reel tape and as cassette
tape for calibrations.

response 22 of 65:

Mar 23 23:49 UTC 2002

        I haven't had an eight track recorder for some time.

response 24 of 65:

Mar 24 12:37 UTC 2002

Heh.  Watch out, Tim.

response 26 of 65:

Mar 24 15:52 UTC 2002

I know where you can get cheap used ones.

response 28 of 65:

Mar 27 10:09 UTC 2002

  Since this is the "Equipment for Playing [Recorded] Music" item,
  I thought I might mention my recent purchase of an Apple iPod.

  I'll write a longer review of it later, but basically the iPod
  is an amazing device with a couple of annoying omissions and
  restrictions that keep it from being perfect.  Still, I'm quite
  happy with it, and can recommend it with only minor reservations.

response 30 of 65:

Oct 14 03:09 UTC 2002

I can't find the previous discussion of MP3 portable players, so I'll
use this item.  I broke down today and got a RioVolt CD/MP3 player.
It was stickered at $99.99, scanned for $10 less than that; the sales
clerk waved a 10% coupon under the scanner and the price went down some
more, and *then* there is a $20 rebate which I darn well better send 
in this time.   So, what, $60-$65 final cost?  Yay Best Buy.  Thanks 
to mcnally for encouraging me to keep looking.
 
There were a frustrating ten minutes of trying to figure out the 
folder navigation, and then it all made sense.  
 
Sounds great on these Spanish folk MP3s by a band called Na Lua 
which I've been playing; certainly those files sound better on the 
the Rio than they do on Winamp on the computers I've got around.

response 32 of 65:

Oct 14 06:18 UTC 2002

"car kit" generally means a cigarette lighter plug-in for power, and 
a cassette tape adapter to carry the audio from the portable unit
into the car stereo.  Most people's cigarette lighters are not connected
to the car stereo for output, but you might have a special model.  :)

As John doesn't have a cassette tape player, he'll most likely
have to get a small radio transmitter which can be picked up by 
your car's FM radio; I have no experience with those.

We were discussing these toys in another item somewhere recently, 
but where?

response 34 of 65:

Oct 14 10:15 UTC 2002

  I've got one of the FM-transmitter doodads that I use with my iPod on
  car trips.  It seemed to work pretty well on my trip from Washington
  down to Utah and around the national parks of the southwest but it was
  a complete failure on a later road-trip from western Michigan to 
  southeastern Minnesota via Chicago.  From about Benton Harbor, MI,
  to Madison, WI, the device wasn't worth using -- about every 20 minutes
  I had to retune to an unused frequency as I came within range of some
  new low-power FM station.