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Date: Thu, 21 Mar 91 14:12:18 -0500
From: "Ihor W. Slabicky" <iws@sgfb.ssd.ray.com>
Message-Id: <9103211912.AA11174@sgfb.ssd.ray.com>
To: tape-heads@fuggles.acc.Virginia.EDU
Subject: Dolby dymanics discussion
From:	DECWRL::"iws@sgfb.ssd.ray.com" "Ihor W. Slabicky" 21-MAR-1991 14:40:25.42
Subj:	Dolby dymanics discussion 

    [stuff deleted]
    
> 
> 	Dolby Laboratories Inc.
> 	100 Potrero Avenue
> 	S.F., CA 94103
> 
> 	(415) 558-0200
 
I called Dolby Labs, and spoke with 'Bob' there.
Here's roughly what we discussed...
 
Dolby is dynamic - depending on the level of signal
being recorded, there is a different amount of 'Dolby'
applied.  Roughly, at high levels, there is no Dolby
effect, in the middle there is some, and at very low
levels, there is a lot - up to 10 dB worth.
 
The Dolby symbols on your deck's meters (usually the
'double-d') is where the Dolby level is for your deck
(i.e. where there is little or no Dolby effect).
It is ~ 200nW/m.  If there is no 'double-d', then the 
Dolby level is 0 dB on the meters.
 
(If you check your meters for the placement of the
Dolby symbol, you'll see it somewhere very near to
the max recommended recording levels for your deck.
What this means to me is that if you record your
tapes at the max recording levels which are recommended
for your deck, the recording level will match the
Dolby level, and there will be little or no Dolby
effect for those passages which are at that level.
Those passages which are below the Dolby level will
get more of the Dolby effect applied to them.  I guess
that if you record a tape with no Dolby, but the levels
are set to the Dolby level, as shown on your deck
meters, then this tape should sound just fine.  This
is just my wild speculation, folks.  This also
supports my theory that you should record tapes at the
highest recording level recommended by your deck's
manual for each tape type, setting the recording levels
so that the PEAKS just hit the max recording level.
On my deck, this means the average recording level
is about -3 to 0 dB, which gives some stretching
room out to the ~ +5 to +10 dB max for Type II tapes.
This way you avoid distortion, which is what starts
happening the more you go over that recommended level.
End of my wild speculation, based on known facts.)
 
Dolby C has a greater dynamic range than Dolby B.
 
Dolby C is much more sensitive to different makes of
tapedecks than Dolby B.  That's why Dolby C on one deck
can sound different on another brand of deck.  Theoretically,
all tapedecks have the same Dolby systems (B or C), because
they are all under license from Dolby Labs.  However, if
one deck manufacturer uses components that are not in spec,
or has a wider tolerances on components, than the
components used by another deck manufacturer, the Dolby
will behave differently between decks.  It's the effect
of hardware...
 
To make the best copies of tapes, dubbing should be
done from a high quality source to a low quality copy...
Going from a low quality source to a higher quality
machine does nothing - 'you can't get blood from a 
turnip'...  When copying cassette tapes, you lose
a little bit (or gain a bit of noise/hiss) with
each generation you make.  You can't get back something
which is not on the tape.
 
In general, one should playback the tape as it is encoded,
(i.e., if the tape is encoded in Dolby B, then play it
back in Dolby B, with the tape type set correctly) and
record the tape on another deck any way you want (your
choice of Type I, II, or IV tape, no noise reduction,
Dolby B, Dolby C, dbx, etc).
 
In general, the best (easiest, less prone to cause problems,
add hiss/noise) way to make copies is to have a tape made with
Dolby B, playback in Dolby B, and record it in Dolby B.
 
Some finer points...
 
A)	If a Dolby B encoded tape is played and the copy
is recorded with Dolby C, this will NOT give you a better
copy.  You don't gain anything from the extra dynamic range
of Dolby C, because of the lesser dynamic range of Dolby B.
In effect, your Dolby C tape can record all these great
dynamic ranges, but because the Dolby B tape has a lower
dynamic range, there just isn't anything to record...
 
B)	A Dolby C encoded tape dubbed to a Dolby B copy
will give you a better sounding copy (than that mentioned
in paragraph A) above), because the Dolby C tape
has a greater dynamic range, and you are capturing
more of it on the Dolby B tape.
 
C)	A Dolby B encoded tape dubbed to a Dolby B copy
will have a very slight loss of dynamics - this is inevitable,
due to the copying process.
 
D)	A Dolby B tape dubbed to a Dolby C copy (paragraph A)
above) theoretically will sound only slightly better
than a Dolby B tape that was dubbed to a Dolby B copy
(paragraph C) above).  The difference would be very slight,
but you probably would NOT notice any difference because
of the inherent losses that do occur when making copies.
 
E)	A Dolby C tape dubbed to a Dolby C copy will
experience the same type of slight loss as described in
paragraph C) above, due to the inherent losses that occur
when copying tapes.  However, remember that Dolby C is
more sensitive to differences in tapedecks, so you
may not benefit from using Dolby C that much...
 
(In all of these cases, the differences are VERY small.)
 
F)	You can make copies of Dolby encoded tapes without
any Dolby.  You would do this by setting the Dolby to off
on the playback machine, setting the playback output levels
to match the Dolby level (by using a Dolby Level Tape),
setting the recording level on the second deck to the Dolby
level (again using a Dolby Level Tape) and recording the copy. 
You do need that Dolby level tape...  Btw, this is what is
meant by matching the levels of the two tapes.
 
(This to me sounds like a lot of work, besides having to get
a Dolby level tape, and matching the levels of the two decks.)
 
That was pretty much the discussion.  The conclusions,
imho, are as follows:
 
Play the tape as it was encoded.  Record the copy the
way you would like it to be recorded.
 
You'd get a better copy by using a Dolby C 'master'
and making a Dolby B copy.
 
You won't go wrong by having the master in Dolby B and
making the copies in Dolby B.
 
Theoretically, a Dolby B tape copied to Dolby C should be
better, than if it was copied to Dolby C, but not by any
amount noticeable...
 
In general, the best (easiest, less prone to cause problems,
add hiss/noise) way to make copies is to have a tape made with
Dolby B, playback in Dolby B, and record it in Dolby B.
 
The recording levels are very important to reducing the
inherent losses due to making copies.  You should record
tapes at the highest recording level recommended by YOUR
deck's manual for each tape type, setting the recording
levels so that the PEAKS just hit the max recording level.
On my deck, this means the average recording level
is about -3 to 0 dB, which gives some stretching
room out to the ~ +5 to +10 dB max for Type II tapes.
This way you avoid distortion, which is what starts
happening the more you go over that recommended level.
 
Direct all flames to me - Ihor

    re .-1	Thanks, Gerry . . . nice job, Ihor

    A lot of Dead tapers don't use Dolby NR and I feel that this is a
    big mistake.  The large dynamic range of a live recording (~50 dB)
    demands Dolby NR to get a good recording on a lousy medium (compact
    cassette).  Many people feel that tapes made with Dolby sound "as if a
    pillow were placed in front of the speakers," but this is due to a
    psycho-acoustic effect: the high frequency spectral content of tape
    hiss augments the high end of the tape, making it sound as though it
    has more high end than it really does.  This becomes very noticeable on
    quiet passages where the tape hiss overwhelms the music, especially
    after a few generations have passed.

    Dolby does have its problems, chiefly compatibility among different
    tape decks.  There's no solution to this, except to trade only with
    people who have reasonable tape decks, which is not to say "you must
    have a Nak"; virtually any low end deck works well new, but after a few
    years they go bad.

>The recording levels are very important to reducing the
>inherent losses due to making copies.  You should record
>tapes at the highest recording level recommended by YOUR
>deck's manual for each tape type, setting the recording
>levels so that the PEAKS just hit the max recording level.
>On my deck, this means the average recording level
>is about -3 to 0 dB, which gives some stretching
>room out to the ~ +5 to +10 dB max for Type II tapes.
>This way you avoid distortion, which is what starts
>happening the more you go over that recommended level.

    I also feel that most tapers set their levels too high.  They have the
    right idea - set the level as high as it can go without distortion -
    but fail to compensate for the fact that the level meters are
    (deliberately) slow and transients often exceed the level reading by
    several dB.  Of course, it's nearly impossible to predict the max sound
    level at a live concert, and I sympathize with them.  I find I get good
    results on type II tapes by setting the highest peak so that it just
    barely flickers the +3 dB light, but every deck and tape brand combo
    varies.  Regardless, I think tapers should leave a little more headroom
    to compensate for meter slowness and the unexpected Phil power chord. 
    If more used Dolby, they wouldn't have to worry so much about getting
    the level high enough to drown out the hiss.  :^)
    
    Jamie

>Dolby is dynamic - depending on the level of signal
>being recorded, there is a different amount of 'Dolby'
>applied.  Roughly, at high levels, there is no Dolby
>effect, in the middle there is some, and at very low
>levels, there is a lot - up to 10 dB worth.

What this Dolby effect IS is varying - depending on frequency and level-
amounts of signal boost (for record) and cut (for playback).

Example:

We're recording, umm.. Weather Report Suite, with no dolby, at the
proper level for the tape deck, lets say the peaks are hitting on +3 db.
When the music comes to a soft part, the signal levels are (of course) lower
and they are recorded by the deck that same amount lower.  When played back,
they play back lower, since of course the music is at a softer part.
Everything's fine..

Well, not really... 
There's Evil Tape Hiss.   Hiss exists at low signal levels. Its a result
of the (analog) playback process.  With no Dolby, you can play back soft 
(low level, that is) music only to a certain amount of low-levelness before
the hiss becomes comparable to the music itself.  For cassette decks this 
is usually around a total of around 55 dB.  This is "Dynamic Range"!

What happens in the Dolby effect is this:
We're recording WRP Part 1 again, this time with Dolby on.  At a soft part,
lets say something at -20 dB ("Now summer rain, tell me why") the tape deck 
dolby circuit boosts the signal level, perhaps 5 dB, before it, gets recorded.  
Furthermore, the amount of boost is greater for mid-upper range frequencies 
than for mid-low bass. Also, the lower the level of the the "incoming" music, 
the more the boost.  A -15 dB signal gets 3 dB of boost, a -30 db gets 7 dB, etc.
Ray Dolby (an audio engineer) figured out the amount of boost vs. level vs. 
freq. that works best, given the state the the art the cassette tape system, 
and the way human hearing works.

Now, we play back the Dolby-encoded WRP Part 1.  The real loud parts 
("Now listen to the thunder shout 'I AM, I AM, _I_AMMMMM_!!!!") are played
back with no change from the dolby decode circuits.  This is OK cause the
loud parts are so much louder than the low-level hiss, that you can't hear
the hiss.   Now, a lower-level music gets played back...  this had been 
boosted during record, lets say the dolby encode figured to add 5 dB to 
mid-range. What would have been a -20 dB signal is on the tape at -15 dB.
Since the Dolby circuit is on, it "knows" to cut the -15 db signal coming off
the tape by 5 dB, to give back the original -20 db signal.  The Big Thing
that happens, how Dolby reduces hiss, is that the very slight amount of hiss 
you would have heard along with the -15 dB signal is also cut 5 dB, making
is more inaudible.  At lower signal levels, more record boost and playback
cut is used, to ensure that the music signal is always recorded louder
("above") than the noise ("floor")

Or something like that ;-).... now that everyones nodded off to sleep, 
I got this whole note to myself!!!  har har har!!  This note is hijacked 
and henceforth will be become the long-absent DYLAN NOTE!!!

Didja see Dylan on the Emmy awards?   I didn't even recognize "Masters of War".
Man what is it with him.  Playing around with his porkpie hat while the 
Academy wuz heapin' praise upon him.  I liked what he mumbled about 
"God rewards those...blah blah blah" though.  Shades of 1963 when he accepted 
the Tom Paine Award from the Emergency Civil Liberties Committee and was wasted
drunk and said he saw a lot of himself in Lee Harvey Oswald and freaked 
everyone there out.

HELP ME I'm turning into A.J. Weberman, Dylanologist & Minister of Defense,
Dylan Liberation Front!!!

 	A.J., ahhh, err, Josh

    
    	        NAK BX300 deck for sale.
        Mint - recently upgraded to gear drive 
        	    $500.00
    
    send  me mail

    Re: .4
    
    sold 
    
    

	I think I should be on a commercial for Maxell XLII's!!!

	This morning I stumbled out to my car in the usual Monday
	morning slump, when, upon looking at a melted snowbank
	I spotted a small object that appeared to be a tape case.
	Upon picking up the tape case, I realized that it was a Boston 
	Garden tape which I had lost in December and the tape 
	was still within the case.  Since December we have had almost
	10 feet of snow, 3 weeks of below zero nights, several ice
	and rain storms......and a few sunny days.  Amazingly, I hopped
	in my car, dried the tape on the defroster and popped it in 
	the tapedeck 5 minutes later.   It sounded grate!!!!

	Maxell XLII's!!!!  Extreme tapes for extreme conditions!!!!  
	  

Hmmmm...don't think I'd have taken the chance of mucking up my Alpine with a 
tape that had undergone that much abuse.  :-)

	dave

	The tapedeck in my car is garbage! 

	I don't have anything fancy for the reason that I used to 
	get ripped off a lot when I worked in Woburn.....

	I did examine that exposed tape on the bottom of the cassette
	before I dried off the enclosure, it was dry, and there
	appeared to be little to no moisture in the tape window.

    
    My tape deck at home just ate its last tape this weekend.
    Anybody have recommendations for:
    	
    		use of two decks  vs.  one dubbing deck
    		Brands
    		# of motors
    		# of heads
    		Dolby B,C, S, HX
    		direct drive (is it best?)
    
                Best place to buy
    
    Thanks for the help,
    
    Steve

Hi Steve, There's a good religious debate on this in Grateful_old. Use 
keywords to find it. Ex-dechead Ger has an Aiwa Dubbing deck which I think 
is real nice, but in general you'll find a lot of folks wont even trade 
with you if you tell 'em you use a dubbing deck, since most of them really 
reduce the quality of the copy...

Get a NAK.
I won't even talk to you unless you have a NAK.



:-) :-)

	only joking!!

    I hope to buy a new tape deck(s) this weekend.  I recently
    moved to New Hampshire and don't have a clue as to where to
    shop.  I know Lechmere's in Manchester, Nashua and Salem, NH.
    Were else should I shop?  I want to see a variety of makes and
    prices.  Anywhere between North of Boston to Concord, NH is good.
    From reading GRATEFUL_OLD I came across Tweeter's, Coumos, Natural
    Sound and Highland Superstore, but I have now idea where they are.
    
    Thanks for the help,	Steve

>                     <<< Note 76.12 by POWDML::PENTLICKI >>>
>                            -< Tape Deck Shopping >-

i bought one of my decks at some place in new hampshire, i think near nashua.
don't remember the name of the store offhand, but if you check notes at all
on the weekend i can find my receipt and post it here sometime tonite if i
remember.

i didn't really do much looking at that shop.  i had decided on the deck i
wanted, but the place where i saw it sold out of it, so i just called around
until i found it.  and it was nice get it in tax-free new hampshire.

- rich

depends what you wanna get: hi-end (nak) or mid-end (sony,pioneer)

for mid-end:
	lechemere in the pheasant lane mall

for hi-end:

	Cookin' in the same mall

Natural Sound is on Rte 9 in Framingham.  Go to the pig roast (or bake) and
check it out ;-)

Good store, but perhaps not the most discounted.

PeterT

    PeterT,
    
    Thanks for the hot tip on Natural Sound.  I went down there today
    during lunch and checked out some Denon decks.  I wanted a 
    single-well, three-head deck in the mid-range prices.  The DRM-740
    fits the bill at $400 retail.  I found last year's Denon 710 model
    with the same exact specs for $360 at Ensemble Audio in Nashua.  I 
    went to Natural and they had it for $329, that's $345 after MA tax.
    Good Deal right?  The guy there (Peter) started quizzing me on what
    I was gonna use it for.  Told him, he suggested Denon's double-well
    dubbing deck from last year's model line for only $360.  Lots of nice
    features (record level control, B/C/HX Pro, bias control and, 
    best of all, you can record two duplicates simultaneously from one
    source).  I still was set on a single, three-head model.  So, he let
    me take the floor model double-well deck home with me to try some
    tapes out on.  If I like it, he'll order me one at the $360 price.
    If I don't, I can still go with the 710 model or nothing at all.  
    
    Thanks again,
    
    Steve

Sounds like yer doing yer homework. Also sounds like a tough choice: 
choosing being able to monitor over being able to dub one more. I look back 
and wish I had a nice dubbing unit when I into the heavy trading.

Heck, ask the guy if you can take home the three head for a while.  :-) 

    No doubt tough choice;
    I'll have a three head if I can get my 1 1/2 year old
    (i.e. no warranty) Sony fixed to stop crunching tapes.
    Monitoring was my number one criteria, until Peter the
    salseman got a hold of me.  There are three-head, double-well
    decks but a bit outside my price range.  Onkyo's got two,
    TA-2800 and TA-207 for $650 and $529 retail.
    Steve

    I have the Denon DRM-800 that I got at Natural and am VERY happy
    with it.
    
    	dave
    

    I'm pretty sure the Denon I tried out last night was the
    DRW-840.  It made a great copy, but still didn't let me
    control the recording level between the two tapes.  The
    guy in the store thought it did and I did too at the time, but
    when I got home and used it, no go.  I gotta be able to 
    control record level between tapes. I didn't have the owner's
    manual so maybe I missed something.  Does the Denon DRM-800
    allow record level control?  What's up?
    
    Steve

I don't know of any dual deck that allows you to control the input level when
dubbing.   They might exist, but I just don't know about them.

My DRM800 is a single deck.  I use a Proton 740 as my play deck.

This is why most tapers run 2 single decks.

	dave

I believe Aiwa's dubbing deck has the dubbing input level control, but I'm 
not sure. Just to confuse you more, Steve, pitch control is another rilly big 
plus if you can find a deck which offers it.

>I don't know of any dual deck that allows you to control the input level when
>dubbing.   They might exist, but I just don't know about them.

i saw a sony deck in a catalog that had individual controls for each deck, and
it did let you control levels from deck to deck.  never saw this deck in a
store, though.

re: pitch control

get it if you can.  i wish i had it.  i don't think you'll find it though, only
on a very high end deck.

- rich

    Yea, the guy at Natural Sound kept talking about setting the
    pitch on two decks so that they ran at the same time.  It looks
    like dual decks are out now 'cause of the lack of record level control.
    It seems like pitch control is out of my price range.  It'd be nice
    though, I've got some tapes where Jerry sounds like he's on helium.
    
    Steve
    

    for me I have a dual deck, nothing fancy just two wells that I can do a
    quick copy from tape to tape, but I have been itchin' for a rilly nice
    single well deck with a pitch control to team up with my dual deck to
    help the tapes that are too soft of off speed (I've got tapes that seem
    to be off speed that I can't bear to listen to)....but I wanna boombox
    with a CD player 1st for my office :') (which has been rumored I'm
    getting sometime soon :') from my lovely wife :')) so if this is true I
    wanna 4 head hifi VCR (two rilly) and a PC with a video toaster 1st,
    and while Im at it I would mind another camcorder (stereo too :')) but
    these can wait as I do have access to this type of stuff at the TV studio
    
    
    dreammmmmmer nothing but a dreammmer, can you put your hands in your
    head ? Oh NO !
    
    Chris

Keep your eye on the Want Advertiser, excellent and well cared for used
decks pop up there all the time, and its a pretty good way to get a high
end deck on a midrange budget. I'm the 2nd owner of an '82 Nakamichi that's
still going strong. Also, repair shops love to tweak into shape your good
old high end equipment.

re > PC with video toaster

Oh, you're looking for an Amiga!  Cool.

re: Pitch control:  Gee, my Sony D6C has this, and it's not too expensive.
At least I don't think I paid too much for it through mail order.  Of
course, since it's basically a Walkman (though a VERY GOOD Walkman) it
is sort of at the top of the line price for those.  It is used mainly as
my playback deck and I've used the pitch feature a few times.  Of course,
until I get my Nak into Natural Sound, it's the ONLY deck I have at the
moment.  Sigh....

PeterT