New Sound Page

Discussion in 'Video Cameras' started by Tony Morgan, Nov 16, 2003.

  1. Tony Morgan

    Jerry. Guest

    So could a couple of bits of wet string, given the right surroundings !..
    :~)
     
    Jerry., Nov 30, 2003
    #41
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  2. Tony Morgan

    Jerry. Guest

    Probably because they don't want to be mistaken for a clueless idiot like
    you Mr Morgan.
    No. Unless you are referring to the fact that web pages can hide viruses and
    HTML emails can be used in a similar manor or the fact that one of your
    sites was un readable.
    Because I have other things to do with my time, but for someone with your
    (self declared) expertises in both video, NLE, web authoring and the fact
    that you are now retired (early retirement IIRC) I would have expected you
    to have the definitive web site - but you have not....
     
    Jerry., Nov 30, 2003
    #42
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  3. Tony Morgan

    Jerry. Guest

    What is a "relatively short distance" ?
     
    Jerry., Nov 30, 2003
    #43
  4. Are we talking about the same thing? A diversity system works in the
    RF part of the system - how would audio phase come into the equation?
    It's designed to prevent drop-outs by giving the receiver two aerials
    to choose from. It works very well, to the extent that it's
    difficult to find anything but the cheapest radio mic system that
    ISN'T diversity.

    My reservation was to do with how effective two aerials would be when
    only slightly spaced. As with semi-pro gear that mounts both on the
    main receiver box.
     
    Laurence Payne, Dec 1, 2003
    #44
  5. Tony Morgan

    Tony Morgan Guest

    Your point is taken, but with some modulation systems (e.g. IEEE
    802.11b/g that uses DSSS modulation) phase anomalies of RF have a
    knock-on effect with the audio component (or more accurately in the case
    of IEEE 802.11, the digital component). IEEE 802.11 is not restricted to
    wireless networking, and is beginning to be adopted for other
    applications because of its relatively reliable error free communication
    with a bandwidth of 11MHz/54MHz.
    Interestingly, the Argos wireless microphone featured on my website
    *does* use diversity reception, in spite of being less the £50.
    It's a function of frequency (or more accurately wavelength). Diversity
    is used to combat the effect of multiple signal paths that would
    otherwise cause antiphase RF signals to cancel each other out giving an
    effective "loss of signal". Theoretically diversity aerials should be
    positioned lamda/2 apart (half-wavelength), but in practice (due to
    "end-effect") they are positioned a little less apart than this
    (typically 0.4 x lambda).
     
    Tony Morgan, Dec 1, 2003
    #45
  6. A typical theatre installation uses a pair of aerials mounted MUCH
    farther apart than this. Each side of the room, in fact.
     
    Laurence Payne, Dec 2, 2003
    #46
  7. Tony Morgan

    Tony Morgan Guest

    AFAIR that technique is to give greater (and more even) coverage. You
    night note that most diversity radio mic Rx boxes have fixed aerials
    spaced as I mentioned above. Sound-stage systems (which is, I believe,
    what you are referring to) are not diversity systems, but multi-channel
    systems. Each mic Tx operates on a separate frequency and are
    colour-coded in correspondence with the mixer controls. And to match,
    you have (up to) six separate receivers within one box.
     
    Tony Morgan, Dec 2, 2003
    #47

  8. A sound stage is a cinema studio, isn't it? I was talking about
    theatre installations.

    My (small) experience of commercial filming is that sound recording
    systems are surprisingly simple: a very few microphones, a simple
    mixer and a DAT recorder synched to the camera by cable or
    occasionally wireless. Any shots where sound would be difficult are
    just captured "well enough" in order to have a guide at the subsequent
    re-recording sessions.

    In TV, I often see stacks of diversity receivers with integral aerials
    in a convenient location behind the cameras, for use with body mics on
    every performer.

    Mostly I'm in theatres. Sometimes the receivers come in racks, two
    aerials to a channel. But, more and more, you see a pair of
    multichannel aerials, remotely mounted as near as possible to the
    stage. These feed a splitter unit, providing two feeds to each Rx
    unit. A few years ago you commonly saw a pair of dipoles, mounted at
    forward lighting positions. More recently, everyone seems to be
    using ingenious active aerials resembling small beehives :)

    I must ask our sound guy tomorrow who makes these.
     
    Laurence Payne, Dec 2, 2003
    #48
  9. I have a 'theatre' system as you call it. It has six receiver modules
    in each rack unit which can be linked to further units. It has the
    usual diversity aerials at each end of the rack unit but provides for
    remote aerials that you can place further away. Maybe we we have the
    sort of confusion, lack of real experience and consequent bad info
    that Jerry keeps referring to. ;-)
     
    Malcolm Knight, Dec 2, 2003
    #49
  10. Sony have two models that I know of.
     
    Malcolm Knight, Dec 2, 2003
    #50
  11. Tony Morgan

    Tony Morgan Guest

    AFAIK the term "sound stage" is a generic one, and (I believe) a term
    used for any wide pickup/coverage sound system. Interestingly I *do*
    know that the term is also used in advanced military sonic systems.
     
    Tony Morgan, Dec 2, 2003
    #51

  12. I've seen the term used to refer to the audio image created by a
    stereo system. As in "I panned the bass to the left of the sound
    stage".

    But we're talking about diversity radio mic receivers, not stereo
    micing techniques, aren't we?
     
    Laurence Payne, Dec 3, 2003
    #52
  13. Tony Morgan

    Tony Morgan Guest

    I think things have drifted a bit. Perhaps because I tried to make the
    distinction between diversity (in this context) and multi-channel
    coverage, which are different.

    I think we all understand what multi-channel operation is. There's a
    good treatment of diversity in the context of wireless microphones at:
    http://www.lectrosonics.com/catalogs/UHFcat0303_05.pdf

    There's some more relevant treatment (though in another application
    area) at:
    http://www.giga-wave.com/giganews_articles_010.asp

    As I've suggested there are parallels in other application areas, IEEE
    802.11 being one such example. The principles (and indeed the circuit
    architectures) are also much the same.
     
    Tony Morgan, Dec 3, 2003
    #53
  14. Yes, you did go off at a tangent! Let's get back on topic. We're
    talking about receiving radio signals from one or more radio mics, not
    about techniques stereo sound coverage,

    Any mics used for general coverage, or attempting a stereo soundfield
    (that's the usual term, rather than "soundstage" isn't it?") are
    unlikely to be radio-linked anyway. Why bother?


    Now, before the scenic trip, we were discussing whether diversity
    receiving aerials should be close-spaced or wide-spaced. I think you
    quoted some math to support close-spacing, I informed you that, in
    theatres, they were typically wide-spaced.
     
    Laurence Payne, Dec 3, 2003
    #54
  15. Tony Morgan

    Tony Morgan Guest

    Then I would suggest that the system is not being used to eliminate the
    problems associated with multiple RF paths, but rather to give wider
    positional coverage from a single mic channel, and if the diversity
    aerials were separated by as much as you say, it would cause more
    problems than they would solve. As seen by one of the links I offered,
    diversity systems are designed to avoid the problems associated with
    multiple-paths rather than to increase the coverage. Since most theatre
    sound consoles have 40 channels (though sometimes less), I can't see any
    virtue in using diversity to give greater sound coverage.

    I would also suggest that the term "sound field" is the plot of the
    sound pick-up associated with a single sound channel (i.e. a single
    mic).

    Having said all that, most professional theatres accomplish coverage
    using static mics (I use the word "static" in the positional sense
    before someone starts getting pedantic and deliberately
    mis-understanding). More accurately, the mic positions are static.
    Wireless mics are usually only used for roving, though naturally there
    are exceptions. And of course we have to remember that only one mic can
    be used with a single diversity channel.

    Anyway, since you criticised me for drifting somewhat, that is (again)
    what we are doing here.
     
    Tony Morgan, Dec 3, 2003
    #55
  16. What ARE you talking about? Theatre sound consoles vary enormously in
    size. And you need one channel per microphone. Whether this channel
    is fed by a diversity receiver or not is irrelevant - there's only one
    channel of audio coming to the board.

    Diversity Rx isn't about SOUND coverage. It's about preventing
    drop-outs by giving a radio mic two chances to be received by two
    aerials. The Rx unit chooses the strongest signal, and automatically
    switches to it. One audio feed is then available to be sent to the
    mixing board.

    Been in a theatre recently, Tony? OK, that's a rhetorical question.
    I have. Lots. And can inform you that the norm is to body-mic each
    principal performer. If there's chorus singing, there may also be an
    array of mics along the front of the stage. Sometimes short shotguns,
    sometimes PZM-type.
    A lot of the time, even this sort of general cover isn't attempted.
    If there's ensemble singing, it will be pre-recorded and performed to
    click-track,.
     
    Laurence Payne, Dec 4, 2003
    #56
  17. OK. That was an entertaining (though unresolved ) diversion. :)

    DOES anyone have any thoughts on whether camcorders are particularly
    electrically noisy, making an unbalanced cable a bad idea in their
    immediate vicinity?
     
    Laurence Payne, Dec 8, 2003
    #57
  18. Tony Morgan

    Darcy O'Bree Guest

    None that I've found but I haven't used every camcorder on the market.
    Given that most consumer camcorders have unbalanced mic inputs it would be
    rather sloppy design to build one in a way that introduces noise to an
    unbalanced cable in its vicinity. Of course, just because it shouldn't
    happen don't mean it that it doesn't!

    --

    Darcy O¹Bree
    Digital Media Studios Manager
    Faculty of Arts, Media and Design
    Staffordshire University

    http://www.staffs.ac.uk/academic/artdesign/mediacentre
     
    Darcy O'Bree, Dec 8, 2003
    #58
  19. Tony Morgan

    Tony Morgan Guest

    Our previous discussion regarding wireless mics in theatres is on the
    back burner from myself as I'm waiting to see Gareth our local theatre
    manager for his view (he worked for 16 years in various roles in London
    theatres prior to coming to Rhyl). I do go to the theatre a lot BTW,
    both locally and on "package deals" to London shows.
    I *believe* it's academic, since both channels at the camcorder socket
    (on domestic camcorders) have a hard (common) ground.

    To provide any sort of noise immunity from a balanced mic you need
    terminate with a balanced input circuit, either an ungrounded
    transformer primary, or the equivalent semiconductor circuit.

    Balanced feeds work because any noise picked up by the cable is in the
    same phase on both lines, and if the feed is to both sides of a
    transformer primary, there is no resulting current through the primary,
    and therefore no transfer of noise to the secondary. Audio, on the other
    hand is in antiphase across the two sides of the transformer primary,
    and therefore provides a current through the primary which is
    transferred to the secondary. Semiconductor circuits (used instead of
    the transformer) accomplish the same thing in a similar way.

    That is perhaps why balanced mics generally have an impedance of 300
    ohms (current drive), while unbalanced mics generally have an impedance
    of 1K (voltage drive).

    Of course, there are active noise cancelling mics, but that is a
    different issue (and operating principle).
     
    Tony Morgan, Dec 8, 2003
    #59
  20. OK. But I thought you KNEW? What's his opinion got to do with the
    price of fish? :)

    Ask him to say hello to my colleagues Barry Daniels and Anna Karen,
    who are appearing in the Rhyll panto, I think.
     
    Laurence Payne, Dec 8, 2003
    #60
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