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Sony SL-2700 Betamax

Discussion in 'Electronic Repair' started by Phoena, May 25, 2013.

  1. You do know that Ampex started the development of VHS before they
    That's new to me. I don't see why Japanese companies aren't capable of
    designing poor-quality products on their own. (RCA had been working on a
    consumer video recorder for years, but felt it wouldn't be marketable until it
    hit the same price point as color TV -- $500.)

    That's not altogether surprising. Beta pulled the tape into an elongated loop
    around the drum, to isolate its motion -- which is why Beta has less line
    jitter.
    I'm not sure I understand.

    You are one of the most-knowledgeable people (about anything) I've ever met,
    but here I have to say "No way, José." VHS has serious time-base problems.

    I first noticed this the early 80s when I was scanning a late-night show I'd
    recorded * -- why was the picture visibly sharper than in normal play? I
    looked closely and saw the reason -- severe line jitter. When scanning, there
    was either less of it (for the same reason analog recorders have less flutter
    at higher speeds), or the eye did a better job of averaging the errors.

    Just as I judge audio equipment by what I hear, I judge video equipment by
    what I see. When VHS recordings have obvious time-base problems -- what am I
    supposed to conclude?

    * The machine was a high-end RCA-branded Panasonic.
     
  2. "Bruce Esquibel" wrote in message
    I owned an NAD MR-20A at one time, and my SuperBeta HiFi machine made
    recordings that were //almost// indistinguishable from the broadcast.
    Obviously, if they were played on modern displays, the loss of quality would
    be more visible.

    You don't need trained eyes to see the difference. It isn't at all subtle.

    You're kidding, of course. One of the most-noticeable problems with VHS is the
    lousy color. Not only are hues sometimes off, but the chrominance doesn't
    always fill the luminance!

    I can't speak for or against the quality of Beta transports. They were
    more-complex than VHS, so, in principle, they should have been less reliable.
    I never had trouble with my SL-HF900 deck. It still works.
     
  3. They probably do those recordings correctly, and the audience for such
    recording will care.

    I've seen pretty recent movies where the surround sound effects are
    completely random and pointless. One movie has surround sound for a bird
    flying around, and it had nothing to do with the scene at all. It's like
    there was a budget for 30 seconds of surround sound and somebody played
    some canned sound effects to meet a quota.

    Then or couse when people were being chased around in the woods and
    murdered there was no surround sound. That would have been the perfect
    time for such effects- hearing some twigs snap over here or there.
    How were those extra channels added and extracted from the regular two
    channel recordings, other than with one of those boxes?
     
  4. "Cydrome Leader" wrote in message
    Point well-taken. Movies often miss the opportunity to create a truly
    immersive experience.

    I had a variety of sources and processors. At the top was discrete open-reel
    tape, which produced the most-spectacular consumer sound, until multi-ch SACD
    came along. (I still have the tapes and an Otari quad deck.) It is unfortunate
    that Sony has refused to reissue its huge library of Columbia surround
    recordings on SACD.

    For quad phonograph records, there was the Audionics Space & Image Composer,
    an advanced SQ decoder that could wrap stereo recordings around you, often to
    great effect. I also had an Ambisonic decoder for Ambisonic recordings. It
    could do things similar to the Audionics, without requiring logic circuitry,
    and did a superb job of ambience extraction.

    For stereo recordings, I had an audio/pulse Model One, the first consumer
    digital ambience device. It didn't generate high echo density, but used
    tastefully, it could greatly enhance the sense of space. (I later replaced it
    with the improved audio/pulse 1000.)

    My current system includes the JVC XP-A1000 and Yamaha DSP-3000 hall
    synthesizers. These are modeled on real halls (such as the Concertgebouw). You
    can pick an appropriate hall (concert, recital, cathedral, opera, stadium),
    then tweak the settings (if you wish) to fine-tune the sound to match the
    recording's ambience. These devices are so natural-sounding, you cannot hear
    them working until you shut them off.

    I have a 6.1 system (no center speaker) with Apogee speakers and Curl
    amplification.

    There is no excuse to listen in two channels. Stereo is technically and
    aesthetically obsolete.
     
  5. Smarty

    Smarty Guest

    Open reel was the best. JVC CD4 discrete disks were the worst......
    Pre-recorded open reel tapes were few and expensive, but boy did they
    sound wonderful.
    My Audio Pulse hissed and made a lot of background noise. The pushbutton
    switch array also got intolerably noisey. The Advent SoundSpace was a
    huge improvement.
     
  6. Smarty

    Smarty Guest

    I had Dayton Wrights, some Quad ESLs, now totally Martin Logan except
    for subs.
     
  7. I had Dayton Wrights...

    I owned Dayton Wright //dynamic speakers// (trade name: Watson). Quite good.
    Had unbelievable subwoofers that got 15Hz -- solid -- out of a tiny box filled
    with SF6. (Sound familiar?) Why no one has "stolen" Wright's long-expired
    patents is beyond me.

    If ever I sell a screenplay, I will replace my belovéd Apogees with the big
    Martin-Logans.

    I don't know who you are, "Smarty", but its rare to meet an audiophile who
    understands the significance of surround.
     
  8. Guest

    "How were those extra channels added and extracted from the regular two
    channel recordings, other than with one of those boxes?
    "
    By summing the left and right channels and sending them to OP AMPS on the inverting inputs, resuling in the attenuation of the L+R component of both channels. By careful mixing, an audio engineer could do alot with that. A system called SQ came out which standardized the process somewhat and only nulled the mid to high ranges, leavng the bass relatively intact for the rearspeakers which were ususally identical to the front speakers, unlike today.. Today, usually nothing under 100 Hz is sent to the rear. Those little satellite speakers couldn't reproduce it anyway.

    The standardization was simply the time constant of the feedback network and the actual amount of L+R attenuation. It was sort of licensed, and you could buy recording supposedly in "SQ", which meant that they were mixed in away to take advantage of the standards.
     
  9. "How were those extra channels added and extracted from
    SQ was a full-range system without any frequency discrimination. The encoding
    and decoding were more-complex than simply adding and subtracting signals.
     
  10. Smarty

    Smarty Guest

    I am not familiar with those subs but you certainly have evoked my
    curiosity! Tiny boxes and 15 Hz --solid-- are not likely
    companions......... My brief flirtation with tiny box subs, ala Carver /
    Sunfire True Subs, was disappointing in that regard, although they did
    make a lot of subsonic energy considering their size. Now I am wondering
    what Wright's sub approach actually was. I still have a remaining
    Sunfire True Sub and some Carver Amazings here with quite an arsenal of
    low frequency drivers, but they have not been turned on in over a year.
    My Logan subs have been from Hsu Research, perhaps a bit pedestrian but
    very nice to listen to.

    If you are dreaming of owning the Logan Statement, I totally understand.
    The Apogees will be hard to improve upon.
    My vocation and avocation since the 1950s has been electrical
    engineering, all things electronic, ham radio, audio, video, computers,
    and the nearly endless array of gadgets which rely on electronics. A CES
    I attended in the 1960s exposed me to the first quad systems then
    emerging, and I had a small hand in working with a Toronto company to
    develop a gated 4 channel decoder using logic to steer rear channel
    content based on primitive rules from left and right amplitudes. Its
    intended market was movie theaters.

    It was very clear to me right from the start that reconstructing some
    information behind the listener had tremendous potential to improve the
    listening experience. "True" quad open reel was a joy to behold, and
    well miked and properly mastered content was just a quantum leap beyond
    anything I had ever heard. Even relatively small speakers allowed a
    credible and extremely engaging sound field. I think I was using AR or
    Rectilinear boxes at that time. There was a collection of open reel
    releases including Joni Mitchell from Verve or some similarly named
    company that were among my favorites. Carly Simon and James Taylor,
    married at the time, did a spectacular rendition of "Mocking Bird" in
    true 4 channel open reel that was another spectacular demonstration of
    the potential of surround. The classical releases were, for the most
    part, wonderful as well.

    As an old geezer, I can attribute my original surround passion to a
    Motorola "Vibrasonic" spring delay reverb installed in my 1962 Stingray.
    Other than the occasional microphonics which arose from the inevitable
    bumps in the road, it created a very satisfying presence and bloom which
    filled the passenger compartment.

    To this day I bemoan the absence of a really rich multichannel format
    for distribution of recorded music. The trend to mediocrity, especially
    mp3, is ironic given the low costs of analog to digital and digital to
    analog converters, storage, etc. If anything, the bar should be rising,
    but instead has been lowering. Was it PT Barnum who said that 'Nobody
    has ever gone broke underestimating the taste of the American public'?
     
  11. Smarty

    Smarty Guest

    The more advanced systems essentially used voltage controlled amplifiers
    to synthesize the rear channels using amplitude and phase relationships
    from the front left and front right to make somewhat sensible decisions
    about when and where to steer energy into the rear channels. The notion
    of a "matrix" to construct the coefficients for the steering logic was
    developed, in which the VCAs and their control voltages had weighted,
    time-dependent control signals. Choosing appropriate time constants for
    the attack, release, etc. was artistic and musically dependent, and the
    eventually winning techniques such as Columbia SQ were noted for being
    comparatively gentle / subtle and without noticeable pumping or breathing.
     
  12. "Smarty" wrote in message
    Sulfur hexafluoride, same as the 'stats. The woofers had a volume of about 2
    cubic feet. When I put 15Hz into them, nothing was audible -- except for
    everything loose in the room rattling. These woofers had extremely low
    distortion -- around 2% at 20Hz.

    Hard, but not impossible. There's an Australian company that makes a version
    with a true-ribbon titanium midrange.

    If by "rich", you mean "supporting a wide range of formats" (such as
    Ambisonics in addition to quadrifontal formats), I agree. But we have at least
    two high-quality uncompressed formats that aren't likely to go away --
    multi-ch SACD and Blu-ray audio.
     
  13. The more advanced systems essentially used voltage controlled amplifiers to
    The correct term is "isolate" or "extract", not synthesize. The rear channels
    are always present. Advanced decoders (such as Tate SQ and VarioMatrix QS)
    selectively cancel the interfering crosstalk, based on which channel is
    momentarily dominant.
     
  14. Smarty

    Smarty Guest

    I would perhaps resort to semantic quibbling in this case, since the
    'isolation' or 'extraction' of a left or right rear channel would
    presume that they had been encoded into the mix in some explicit way to
    begin with, and could thus be extracted using some reciprocal process or
    decoding scheme. The original front channels did not possess the
    bandwidth nor the dynamic range to permit separate channels to be
    encoded, and any scheme which claims to fold 4 channels into two and
    then magically permits the original 4 to be regenerated would need to
    use alternate modulation schemes, thereby rendering downward
    compatibility with existing stereo to be none existent. Fundamentally,
    you cannot take two channels of 20 KHz bandwidth and (let's say) 70 dB
    of dynamic range such as may be found in a standard LP record and
    somehow encode anything additional without either spoiling the original
    stereo L and R pair, eliminating conventional stereo playback, or
    creating a new and different encoding scheme from scratch. JVC
    approached the problem with adding an ultrasonic subcarrier and then
    modulating it, adding true additional channel capacity in the process
    (in much the same manner as FM monaural added FM stereo with its similar
    pilot and subcarrier multiplexor). Sadly, the JVC ultrasonic subcarrier
    imposed on the vinyl, groove, was both extremely fragile and very
    susceptible to noise, despite the specially shaped and designed stylus
    by Shibata which knew how to deal with it.

    My distinction between 'synthesize' and 'extract' really goes beyond
    mere semantics, and is quite explicit in communications theory in terms
    of signalling and channels, in that uncorrelated content in the 4 quad
    channels demands more than mere phase shift nulls, cancellations, or
    gated VCAs which temporarily steer energy from one place to another. The
    original 2 stereo channels could have encoded 4 true channels had
    engineers been allowed to sacrifice backward compatibility and trade
    bandwidth for dynamic range, for example. Or they could have
    incorporated some in-phase and quadrature method to modulate sidebands
    of a suppressed carrier or exalted carrier encoder (such as NTSC color)
    or used some (1960's vintage) TDMA mux approach. Or as a partial
    compromise, they could have put control tones / signals in the
    ultrasonic band above (let's say) 15 KHz and done some low pass
    filtering on the front channels and used the control tones to steer some
    rear VCAs.

    They opted to preserve quality and compatibility, and in doing so
    created a two channel mix from which extra channels could be
    synthesized, but the isolation / extraction of true rear channel could
    at best transpose out of phase information into rear channel output as
    if it were somehow supposed to be there in the first place.
     
  15. The correct term is "isolate" or "extract", not synthesize. The rear
    'isolation' or 'extraction' of a left or right rear channel would
    presume that they had been encoded into the mix in some explicit way to
    begin with, and could thus be extracted using some reciprocal process or
    decoding scheme. The original front channels did not possess the
    bandwidth nor the dynamic range to permit separate channels to be
    encoded, and any scheme which claims to fold 4 channels into two and
    then magically permits the original 4 to be regenerated would need to
    use alternate modulation schemes, thereby rendering downward
    compatibility with existing stereo to be none existent.


    This is absolutely true mathematically -- but it is not true
    psycoacoustically. The ear can be tricked.

    It is possible to have significant material on all four channels at the same
    time, with the resulting effect seeming fully "discrete".

    Actually, the "alternate modulation schemes" you refer to, do allow full
    backward compatibility, just as stereo FM broadcasts can be heard in mono
    without losing anything.


    you cannot take two channels of 20 KHz bandwidth and (let's say) 70 dB
    of dynamic range such as may be found in a standard LP record and
    somehow encode anything additional without either spoiling the original
    stereo L and R pair, eliminating conventional stereo playback, or
    creating a new and different encoding scheme from scratch.

    Again, yes and no. SQ encodes the front left and front right channels as if
    they were conventional stereo, so they sound pretty much the same as they
    would on a stereo record -- or when an SQ disk is played in stereo.

    It is worth noting that Ambisonic UHJ encoding allows psychoacoustically
    correct playback without logic circuits.

    Of course, the availability of "discrete" delivery systems largely eliminates
    the issues of compatibility.
     
  16. Smarty

    Smarty Guest

    Indeed it can. I was talking in the parlance of an electrical engineer,
    ultimately predicated upon the underlying mathematics of communications
    theory and its vocabulary.
    Yes, this is true, but this ear/brain trickery comes at a price.
    Engineers would not call this a discrete system since the effect is
    artificially created, aka 'synthetic'.
    Only one alternate modulation schemes I mentioned does offer backwards
    compatibility, which is why JVC chose it for their CD4 vinyl LP system,
    at the expense of rapid wear-out and very noisy rear channels, mitigated
    somewhat by companding and severe filtering of highs in the rear. The
    other modulation schemes I described do not offer backwards
    compatibility unless the original front left and right channel
    performance is degraded.
    The kernel of your semantic distinction in that we are dealing with
    extraction and isolation of rear channel information which has been
    encoded and added into 2 standard front audio channels, ostensibly
    without compromise to the original front channel pair.

    I entirely agree that psychoacoustic techniques permit the illusion of 4
    (or more) channels to be constructed in the listener's mind. The brain
    has a lot of adaptive power, and mp3 recordings with less than 15% of
    the originally encoded music are generally accepted as reasonable
    approximations to the original recording as well. Perhaps we hear what
    we want to hear or what we choose to hear.

    To the engineer however, the distinction between extracting an isolated
    signal which is independently signaled versus the synthesis of a derived
    signal which is not explicitly and discretely separable are two entirely
    different methods. The fact that the human brain can be fooled to think
    that the more complex discrete version can be adequately imitated by the
    less complex derived version really doesn't change the technical
    distinction between real versus synthetic.
     
  17. To the engineer however, the distinction between extracting an isolated
    signal which is independently signaled versus the synthesis of a derived
    signal which is not explicitly and discretely separable are two entirely
    different methods. The fact that the human brain can be fooled to think
    that the more complex discrete version can be adequately imitated by the
    less complex derived version really doesn't change the technical
    distinction between real versus synthetic.

    I never said it did. I object to the term "synthetic".
     
  18. Smarty

    Smarty Guest

    The word "synthetic" is not in any way used in a negative or derogatory
    fashion in the engineering context. Synthesis, analysis, and other such
    engineering terminology are understood to mean rather concrete things
    which may offend those who tend to thing of them in a more informal or
    colloquial way. The rear channel information in such systems as Columbia
    SQ is synthetic, having not been discretely processed as it would be in
    a system explicitly designed to capture and then reproduce such rear
    channel information. In fact, an SQ system could not localize a left
    rear only signal nor a right rear only signal without producing some
    artifacts in the front channels, given the non discrete nature of the
    method employed. It is an implementation distinction which may be
    noticed or may not, but it not at all like you make be thinking of if
    your objection views synthetic = "ersatz", unrealistic, etc.
     
  19. The rear channel information in such systems as Columbia SQ
    That is absolutely incorrect.

    In all four-channel matrix systems, there are four inputs and four outputs. A
    logic-directed, phase-cancellation decoder is capable of dynamically
    "separating" the front and back information.

    Of course it can, as assuredly as it can simultaneously localize left-front
    and right-front signals, without any artifacts in the rear channels.

    It can do this for //any two// isolated channels. The decoder cancels out
    their crosstalk in the other two channels. This breaks no laws of math or
    physics.

    I own two hall synthesizers, which produce synthetic ambience -- which happens
    to sound very natural.
     
  20. Smarty

    Smarty Guest

    I have several hall synthesizers presently including a relatively
    elaborate Audyssey processor in my main system, and I have owned many
    going back to the AudioPulse 35 years ago (and its annoying hiss and
    pushbutton intermittents) and many, many since then. Many if not most of
    them sounded and presently sound extremely natural. And this discussion
    has absolutely NOTHING to do with their ability to create a convincing
    and natural and wonderful sound. I entirely and totally share your
    opinion and do not have any disagreement with your assessment of their
    performance from a psychoacoustics point of view whatsoever!! Had I been
    a critical reviewer of this equipment and been asked my opinion of how
    they sounded, I would totally express my vote of approval and
    confidence, and have, indeed voted many thousands of my dollars directly
    over quite a few decades supporting this very belief. Even my small
    audio system in a tiny small home office has a $2K Denon receiver with
    an Audyssey X32 processor because I totally enjoy the perceived effects
    of its natural surround sound.

    However........

    I am now (and have been) exclusively talking from a technical,
    engineering viewpoint, and as one who is very qualified in this area.
    The various systems which do not provide separate and discrete
    independent channels for each of the 4 original channels cannot, do not,
    and will not separate and maintain independent information for each of
    the four channels unless each has its own distinct, isolated, channel. A
    channel has a very specific and very defined meaning to a communications
    engineer not only based on bandwidth and SNR but also its time domain /
    frequency domain characteristics, a snapshot of which can be portrayed
    in its transfer function, and measured entirely using both time and
    frequency domain techniques including Fourier and Laplace analysis. I
    spent 2 years in a Masters program learning this topic quite fully on
    top of the (4 courses of) required undergraduate electrical engineering
    course work required for this area.

    You might be convinced that some matrixed scheme of putting 4 audio
    channels into a 2 channel stereo medium can somehow permit the originals
    to be faithfully extracted, but I am here to tell you that you are
    entirely wrong.

    The more advanced version of SQ used gated, voltage controlled
    amplifiers not unlike the more recent Dolby ProLogic scheme to move out
    of phase information selectively to the rear. The encoder can and
    certainly does encode the rear channels to be out of phase so as to
    emphasize their rear presentation, BUT..............and this is the
    killer issue...........the original stereo mix already has out of phase
    information which itself conveys time differences attributable to front
    separation alone.

    The lack of separate and independent channels forces the scheme to
    "guess" at which elements of the signal structure represent true rear
    data, which represent original left to right phase differences, and how
    to use some form of demodulation to portray them. The appearance of
    multiple approaches using several competing matrixing, AGC, companding,
    and steering techniques and competing ways to trick the ear clearly
    illustrated the absence of a single correct solution, since the 4 into 2
    back to 4 channel process is inherently very inexact.

    The decoder has no way to "cancel out crosstalk". The 2 channel phase
    information does not contain identifiable crosstalk since the front and
    rear are not orthogonal, and have no clock or other time reference to
    independently serve to distinguish front from back out of phase content
    versus left to right out of phase content. Were an ultrasonic clock to
    have been recorded (an approach considered as one potential solution
    versus an ultrasonic subcarrier used by JVC), and this clock used to
    time mux the analog stream, then there could indeed be a way to
    explicitly isolate separate channels, but at the expense of front
    channel bandwidth and signal to noise. In the subsequent digital era,
    these problems disappear, and bit pooling and TDMA or other muxing and
    sampling allow streams to be created where time can be used as a
    reliable reference to sort things out. In the early 1960s when these
    systems were being deployed (and I was in my graduate EE program) this
    was not an option.

    Try to imagine what a stereo capable LP would contain in order to create
    a left rear only output:

    If you had only left energy recorded, it would show up in the left
    channel regardless of phase. Left energy alone would have no phase
    difference to reference, and its absolute phase would either cause the
    left front speaker to move its cone first forward then back, or, if 180
    degrees reversed, would move the cone in the opposite sense. Any phase
    angle you choose for conveying "front to back" for this simple example
    fails.

    If you want to build an encoder / decoder to use phase as a way to
    convey front / rear directionality, you can ***SYNTHESIZE*** an
    artificial reference frame, exaggerate the effect with VCAs and gating
    logic, and treat shorter phase shifts as if they belong to the front and
    longer phase shifts as if they belong to the rear. The ear can indeed be
    fooled, and this is fundamentally the way it was done.

    Lets go one step further and make an even more drastic engineering
    assumption. We are going to assume that the front speakers are spaced
    much closer to one another than the rear pair are spaced with respect to
    the front. We will then "guess" that phase shifts / time delays longer
    than the presumed short left to right delay are entirely attributable to
    rear delayed energy. We will choose an arbitrary cut off and declare
    that all delays longer than "X" degrees of phase shift are the result of
    rear channel content. This might even work were it not that 361 degrees
    of phase shift is entirely and totally indistinguishable from 1 degree
    of phase shift as far as analog processing is concerned. Phase only
    offers a brief impartial piece of evidence as encoded in this analog system.

    Could an advanced DSP be used to build an FFT waterfall and distinguish
    early and late energy more exactly. Yes, of course. But this has nothing
    to do with the way SQ, QS, Dolby ProLogic or any such primitive scheme
    worked in the 1960s.

    Did I ever say that SQ or other techniques of its ilk were bad,
    unnatural, or otherwise flawed. Not at all. I ask you please to not
    conflate how things work with how things sound. I am an engineer talking
    about how things work.
     
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