Conference napalm::commusic_v1

    Seems like CrO2 tape with 120 usec EQ with Dolby encoding would be
    bound to sound, um, "bright"....
    
    Edd

    Let's not confuse bias and EQ.  You still need a higher bias level with
    chrome tape.  
    
    The 70 us EQ was developed by Advent in the early 70s to allow trading
    the headroom of *true* CrO2 tapes of the day off for lower hiss by
    boosting highs on record and cutting them on playback.  However, it
    wasn't until the mid-70s that other manufacturers agreed to this; I
    still have an old Sony deck that uses 120 us EQ for type II tapes. Many
    older decks allowed you to choose which EQ to use when recording, and
    you chose the same EQ on playback to compensate.  The reason 70 us
    din't work with "normal" tape is that the additional high end would
    cause saturation; CrO2 formulations had about 6 dB more high frequency
    headroom than the best normal tapes (the *early* versions of TDK-SD and
    Maxell UD), but were sensitive to saturation in the *low* end. Advent
    reasoned that if they used some of the extra headroom to allow boosting
    highs on recording, then on playback, an additional hiss reduction
    would be realized.  
    
    By the mid-seventies, the development of non-chrome type II tapes
    (TDK-SA was the first of these, using a cobalt doping) arrived with
    improved overall headroom, and less head abrasion.  Since then, only
    BASF has persevered with true CrO2 tapes, partially because DuPont (who
    marketed the first CrO2 tape, Crolyn) owned a patent on it, and
    required royalty payments.  For those aged enough to remember type III
    tapes (ferrichrome), this was a Sony invention that allowed the
    improved low end performance of a normal tape with the better high end
    performance of a CrO2 tape.  This type dropped from the market quickly,
    as the improved cobalt-doped type IIs began to be available (I haven't
    seen a deck that took type III since the early 80s, or any type III
    tapes but it *did* exist, for those who wondered how metal got to be
    type IV).
    
    Most commercially released type II tapes are done with 120 us because
    many cheap cassette machines don't have playback EQ switches.
    
    The Dolby cal thing is a wash.  It's mostly due to azimuth problems in
    the transports (Karl, you have a Nak and know what *they* did to
    control azimuth).  If the alignment is off just a bit, the Dolby
    mistracks and takes out more highs than intended.  The alternative is
    more hiss for those who *want* to use the Dolby on playback anyway.  I
    would use Dolby myself.  All of the various attempts at "audiophile"
    cassettes in the past (notably the Advent cassettes and the Windham
    Hill/Nakimichi series) have used Dolby, I think the WH/Nak tapes used
    Dolby C on metal tape.
    
    Nowadays very few commercial relases are done without Dolby B, and HX
    Pro has become quite common as well.
    
    						Brian
    
    P.S.  Am I the only person out there who doesn't have problems with
    Dolbyized cassettes?

    Would the old TDK-AD series tapes be type III?
    
    Edd

    re: .2
    
    >    P.S.  Am I the only person out there who doesn't have problems with
    >    Dolbyized cassettes?
    
    Brother you've missed an awful lot of my notes.
    
    I've slammed Dolby B (in particular) at every opportunity.  Like,
    look in the "what 4-track should I buy" notes.  My first priority
    is "no dolby B" and I have always given this reason:
    
>    Skeptical, I spoke to two large duplicating houses.  They both admit
>    that the QA on the Dolby chips in everyone's cassette decks is non-
>    existent.  But they both stated that it IS a standard, that over 95% of
>    their music jobs are B encoded, and that if the tape is B encoded, the
>    worst that can happen is a bright top end on a no-B deck.  
    
    
    This makes me feel good, because I've been forwarding this hypothesis
    for many years without any real substantiation.
    
    To me, Dolby B on most decks sounds like nothing more than a high
    pass filter.
    
    		db

    Thanks to everyone, esp. .2, Brian - encyclopedic !  I was equating
    EQ with bias.
    
    db, it seems the studio owner I spoke to really agrees with you. 
    However, I have decided to go with Dolby B, if only counteract all
    those poorly-adjusted decks and systems with the speakers on the floor-
    the high freq boost with B ought to help, especially if the public
    plays tapes with B on.  I got used to hearing my music with real clarity 
    off PCM, and am almost thinking there's no such thing as too much 
    high end on a cassette dub.
    
    It's clear Dolby B is a compromise.  On a good deck (aligned, playing a
    tape it's biassed for) it works well.  But as I said B-chip QA on millions 
    of cassette decks means that many, if not most, might not work well.
    Speaking of "Dolby B CHIPS", I have an early-to-mid-'70's TEAC Dolby B
    encode/decode unit, meant for use with large open reel dex.  It came
    with a 400Hz calibration tape.  This thing is as big as an FM tuner !  
    I find it fascinating that all that circuitry could be reduced to one 
    chip with the same sonic quality. Or maybe it hasn't, and that's why 
    Dolby B's reputation is somewhat tarnished these days.
    
    karl
    
    p.s. "Dolby B" is a registered trademark of Thomas Dolby Labs, Inc.

    Well, again , "QA" isn't the best description of the problem.  Dolby
    requires level calibrations, which are typically done by setting PB
    level to a standard test tape, than setting record level so that when
    the tape is played back, the PB level is correct.  Of course, every
    time you pop in a new tape, the level may need to be tweaked. 
    Expensive decks may have the cal adjustments and oscillators to make
    the tweaks, cheap ones don't and calibration suffers.  Things get worse
    as you swap tape types.  Even not cleaning your heads between recording
    two tapes can cause level shifts.   *Then* when you add in the level
    losses due to head misalignments, dropouts, etc. you've got serious
    problems.  That's why the new Dolby S liscencees have to show that
    their transports meet a certain rigid spec on alignment.  
    
    I can guarantee you Dave, that I can make Dolby tapes on my deck (which
    has the cal features) on a 99 cent tape that will sound identical to
    the non-Dolby copy except for the hiss levels.  I paid $750 for the
    pleasure.  8^)  8^)
    
    The only reason dbx desn't act like a filter is that it acts over the
    full frequency range, i.e. it is not sensitive only to higher
    frequencies.  But you can have misaligned dbx as well, this results in
    audible "breathing", and dropouts are magnified due to the high
    compression/expansion ratios used.
    
    Edd, the old AD was a type I.  As I recall, neither TDK or Maxell ever
    did a type III, but Sony and BASF (both of whom sold *true* CrO2 as
    well) did.  
    
    							Brian

    A consideration might be that the vast majority of people listening to
    your cassettes leave the Dolby on all the time and will not pay
    attention to the *absense* of the Dolby logo and turn it off.
    
    So if you send your tape out unencoded, and everyone listens to it
    with the decoder on, they really *will* lose the high end!

    Not directly related to formulation, but...
    
    Is there a difference in thickness among C60, C90, and C100 cassettes?
    I've been told that C120's are thinner, but what about the others?
    
    Rodney

    In the open reel days, thickness and length were indirectly
    proportional, i.e. a 1200 ft. 1.5 mil tape, 1800 ft. 1 mil tape and 2400
    ft. 3/4 mil tape all fit onto a 7" reel.
    
    This proportionality is still true in cassettes, though some brands use
    the same thickness for all lengths.  The tipoff is how large the hubs
    are (larger hubs for shorter lengths) or the "pack" of tape looking
    smaller for shorter tapes.
    
    Some premium types actually state on the package what the thickness is.
    
    The old saw against using C-120s (anyone remember the TDK C-180?) has
    been somewhat forgotten with newer transports being built better, the
    trend is clearly towards C-100s from C-90s, and TDK has been pushing a
    C-110 of their metal tape.  Still, for archival applications,
    shorter/thicker tapes will hold up longer.
    
    							Brian

    
    
    
    		What about "metal" tape formulations?  How does it compare
    to type II tape.  ...bias, EQ, response, durability,  compatability..
    
    
    		             ????????????????

	Recordings I've made with metal tape and dBx (TM) are so clean and
	noise-free it's uncanny.  But then I've never heard a CD on a hi-fi.
tom

    Re: .10
    
    Metal tape requires a higher bias current than type II tapes (which
    require higher bias than type I).  The EQ used is 70 us, same as for
    type II.  Frequency response is potentially superior to type II, but on
    very good decks it may not be noticeable.  What *is* noticeable is that
    it saturates at much higher levels, allowing cleaner reproduction of high
    frequency signal transients. 
    
    It's compatible on *playback* with any deck, but decks not equipped with
    the right bias circuits cannot record on them correctly.  Durability is
    claimed to be superior to oxide tapes. 
    
    
    							Brian