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Audio to Cameras

Discussion in 'Sound, Music, and Intercom' started by mbenonis, Sep 7, 2003.

  1. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    Hi everyone, I'm Mike Benonis, and I go to Stone Bridge HS (the same one Dave went to). For our first play this year (Feiffer's People, for those who care), I'm experimenting with using a number of cameras to film the production, so we can edit it down later for various things. The problem I'm having is how to get consistent sound to the cameras.

    Here's what we've come up with so far:
    We take a group output from the board (Spirit 24), and run that down from the booth to a splitter of some kind. I've toyed with various ideas here, from a bunch of lovely Y-cables, to a press box, to building our own press box. Does anyone have ideas for this? From there, I'll distribute the signal to the 5 cameras in the house, and on each one I'll build a custom XLR female to 1/8" adaptor cable (we're dealing with library-grade cameras here).

    We're also going to have a camera on the catwalk, and I was thinking we could "hijack" an intercom cable run and use that to send the audio up (to avoid messy cable runs).

    Does this sound like a feasible plan? Does anyone have any suggestions to improve on it?

    Thanks,
    -Mike
     
  2. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hi Mike, welcome aboard.
    To answer your question--your best idea is to run your main audio feed to a press mult. You would best have an ACTIVE PRESS mult rather then a passive--but a passive will work in a pinch. Reason being is that press mults are transformer isolated and have ground lifts, and some will match the impedance usually (a must when sending to video cameras), and since many different cameras plugged in to different areas around a place may be on differing ground sources you want to isolate them from interference and each other. So to avoid hums and get the best possible feed, the press mult works best. The level to these on some of the nicer mults can be indiviually monitored for level too. In a bigger pinch--you can buy the Whirlwind Splitter boxes..usually they are 1in and 2 out, or 1 in and 3 out and those should work too. Using a Y cable for so many will split your signal too many times and you would then be interconnecting the camera's together as such. Best to isolate them using the splitter or press mults. As for stealing a line for i-com to send your signal--that is fine provided that the line is not connected to a main source run and can be isolated..you do NOT want to send com line and power to your camera's. This will involve you checking out yoru line run up to the cats and see where it comes out to. if its an individual cable that just taps into and does not have a com loop thru--where cable loops from that box to another com source or feed elsewhere then you should be able to do this.

    Hope this helps...
    -wolf
     
  3. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    Thanks for the quick reply. You bring up a good point with the camera interconnection, but I don't know that we'll be able to afford a decent press box as of now. How much would you say they would go for?

    As far as Whirlwind boxes, how much do these go for usually? I don't believe that we have any around (although I'll ask).

    If we can't get whirlwind boxes, can you think of any mediocre solutions that would work? Perhaps using all 4 group outputs and splitting them once with a Y cable?

    I'll test out the intercom cable and see if I can get a clear signal from one end to the other (it looks like each intercom run is a separate cable from looking around in the rack). Dave, if you're reading this, would you happen to know whether they are separate lines?

    Thanks,
    -Mike
     
  4. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya,
    well a decent press mult to BUY would be in the thou$ands of dollars usually. But you can rent one for a week for a couple hundred bucks. RCI Sound is the best source in your area for renting this. The Whirlind stuff usually run about $60-80 per splitter box..and they come in 2 or 3 way splits.


    -wolf
     
  5. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    Hmm, that's out of our price range, especially for a job this small. We're talking about a 35 minute play that I'm experimenting with here. :) However, while surfing aroumd I found a small press box by Horizon called the PB-8. Do you think it's worth purchasing? Or would it be just a waste of money?

    http://www.northernsound.net/Sales/displitters/horizon/horizondi.html#PB8

    -Mike
     
  6. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya,
    The PB-8 is a passive direct box--it has isolation transformers which is a good thing. It will work fine for your application--however I checked the price from Northern you posted--a bit high if you ask me. Try Full Compass for a similar box.. www.fullcompass.com or Markertek in NY.. www.markertek.com and they should have better prices on similar units. Also--those company's have discounts to educational institutes like schools so you can get better prices then they advertise.

    FWIW, RCI systems also makes these boxes and many other styles custom....and RCI is in Maryland.

    Hope this helps...

    -wolf
     
  7. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    I'll give these companies an e-mail or call tomorrow and see what they offer (a quick glance didn't reveal anything). It's good to know that they offer educational discounts on these products - it will help a lot!

    I appreciate your help with all of this. :)

    Thanks,
    -Mike

    PS - One thing, for this application would you agree with me that I should definitely be using XLR cable? I ask because our head tech suggested going with "cheap" RCA cables to save money, but I actually found XLR to be just as cheap to get (from www.gigcables.com) as RCA from other places.
     
  8. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya Mike,

    At Full Compass--ask for Dawn..she's a real great sales person. At Markertek--ask for Ray(he's in educational accounts).

    Couple of things to your last question--XLR is the BEST choice for several reasons. XLR is BALANCED cable(3 conductor--2"hots"+1ground)--RCA is UNBALANCED(2 conductor--1"hot"+1ground). If you're not familiar with the main difference between the two types of cables, or CMR(Common Mode Rejection), then suffice it to say without going into too much technical detail you may not want to know yet, that a typical RCA output will not travel a long distance(15-20feet maybe)--and being UNbalanced you risk line-loss, signal drop and you risk interference from RF and electrical / ground signals getting piggybacked onto the signal. You reduce that to near elimination with a BALANCED XLR cable. Theres a reason you see 50' or longer XLR cables, but you never see a 50' RCA cable(they are usually sold in 3'-10 lengths at most)...


    So stick with XLR--and your mini 1/8" TRS plug you were going to make adaptors with, and you will be fine. =)

    Hope that helps..feel free to ask any further questions that come your way. ;)

    -wolf
     
  9. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    I'll do that.

    As for XLR, that what I thought. I read the tutorial about balanced vs. unbalanced, and it makes a lot of sense to me (technical things in general make sense to me :)).

    Thanks again!
    -Mike
     
  10. Jo-JotheSoundDog

    Jo-JotheSoundDog Active Member

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    Okay I am not pretending to know anything about video here at all.
    But wouldn't it be easier to just make one copy of the main mix and add it to the video in post? It seems like it might be cheaper and easier to get ones hands on a video editor.
     
  11. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Ah yes..my favorite video phrase: Fix it in Post. =) Well in a sense it would be easier to add the audio later--however it has been my experience that to do so requires equipment that I don't think most high schools has the ability, or skilled folks, to do. Audio to be added in in Post HAS to be time-coded or it wil never sync right with the video and it will look like a bad chinese kung-fu movie dub. The video is also coded, and both codes need to be sync'd up to run simultaniously. I assume these guys will be doing some kind of master that is cut/edited from all the copies, but they would then need to sync up each edit with the proper time code audio and adjust. Plus--All camera's have to run in the same speed, and they have to have the editing and post facility/gear to do this in. Its a lot easier nowadays with the computer programs etc...but for high school it may just be simpler to edit the completed videos with audio.

    just my thoughts on the issue...but then you may be right and they may have the whole post edit facility--and if so they just need to do SMPTE time-code and sync everything up.

    -wolf
     
  12. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    Wouldn't that be nice. However, we are using the cheap cameras from the library and the best thing we have in the way of editing software is Primere. It *can* be done, and I know someone who has done this before, but it would be the least desireable option.
     
  13. Jo-JotheSoundDog

    Jo-JotheSoundDog Active Member

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    As I said before I know almost nothing when it comes to video. But years ago when I was in high school I had at least three friends whose fathers were big into video-taping everything. And after a couple of monthes they were buying all sorts of video editing gear. I remember when we had to do any type of video work, these fathers would come out of the wood work to show off their toys. I just figured that in this day and age all this stuff has become much more affordable, so more parents would have this stuff.
    And secondly just a question, but it seems to me like with the cable runs and splitters there is already going to be a little of a delay, am I wrong?
    I'm not trying to be a pain or even devil's advocate. I am trying to learn something here as well.
     
  14. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    As far as the latency, you do have a point here. I haden't put much thought to it, but that may be worse than trying to pin down the video and sound in post.
     
  15. dvsDave

    dvsDave Benevolent Dictator Administrator Senior Team CB Mods Fight Leukemia

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    Because of the small distance involved (less than 200' total), I don't believe the delay would be noticable...

    however... i would check with wolf on that one...
     
  16. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    I'm not a video guy--but I will tell you what I know and explain it as I have been taught about it. To answer jo-jo and follow up on this point--yes there IS a very very small delay, but there is also a delay in the actual video recording too. Between the actual image and the transfer of the image to tape--there is a small delay of real-time from video time. This is occasionally evedent in some IMAG situations where the speeds of the projectors and tape machines are not in sync or the image is passed onto tape first and then played back from the tape to live-image. The actual delay time is in the millisecond range...my guess would be in the 2 or 3 milliseconds range--however a delay generally does not become audibly noticable or a problem until it goes past the 10-20 ms range. Those kind of lengthy delays in audio are usually cause by acoustic energy travelling freely in a given open space in proportion to the position of the actual microphone--and that given space can be effected by reflection, temperature, humidity etc etc. FWIW, the speed of sound is in the 1130 feet per seconds range at ideal conditions...

    Now--As for the "distance" of the cable being the main cause of the delay--not really. The "speed" of electricity--and that is what we are talking about--electricity, since the signal is voltage, is nearly immeasurable because electrical charge in a continuous copper cable happens at nearly instantatious speed since all the electrons et al get "charged and pass the charge on to each other almost instantly. Voltage is a constant--its either there or its not--instantatioously for discussion purposes. Its like light-speed...186,000 miles per second rounded off..its that fast. Delay you would notice from the video and audio beingsyned up is the SPEED of the tape/recorder and the video frame-per-second recorded.. Again--if audio and video are NOT sync'd up by a time-code and all gear does not run at the same speed--you can get minor delay problems trying to sync things together.. I'm not a video expert either...but I have been around enough vidiots to know a few things. If anyone else has more video experience then me--I'd love to learn more myself. If I get a moment to breathe ion the next few days, I'll ask a few friends at a TV studio I work with if they can better explain this to me and I will pass that info on here for all to learn from.

    hope that helps clear things up some...delay from a speaker source and delay from a signal travelling down a cable is like apples and oranges. Now--if the Mic's for recording this happen to be over 50 feet or so from the sound source--then you are recording a delay rather then picking up the direct sound source directly from a lav or on-stage mic. More to think on... ;)

    -wolf
     

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