Any good A/V sound guys here?

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russellhltn
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#11

Post by russellhltn »

jeffphil wrote:So when an attenuator is sufficient, a transformer isn't going to do anything any better in this sort of application?
Correct. In fact it can make things worse. Transformers have a limited frequency response. Not really an issue for this application, but it would for high fidelity audio.
jeffszone
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#12

Post by jeffszone »

Is there any kind of filter or gizmo that will reduce the background "hiss" or "hum" that is always there? I imagine deleting such sound would distort musical pieces, but for just people speaking I am wandering if there is anything that can make it go silient in between words/sylables instead of that constant hissing noise. I think a small part of the hiss is inately part of the video phones themselves.

Thanks for all your help! You've been awesome! (I really need to sit down and get more up on audio gear.)

-Jeff
russellhltn
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#13

Post by russellhltn »

Generally you shouldn't hear any hiss or hum. That suggests that the levels aren't set right. I'm still wondering why you are getting mic levels out of a line level out. Just the normal background of a line level out is going to have a fair amount of noise because the signal is supposed to be much higher. Did you get a chance to check the two jumpers in the back and make sure they were set the way the book said they should be?

Either that, or try the attenuator cable again. The attenuator will take everything down and then you can turn up signal.
jeffszone
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#14

Post by jeffszone »

RussellHltn wrote:Generally you shouldn't hear any hiss or hum. That suggests that the levels aren't set right. I'm still wondering why you are getting mic levels out of a line level out. Just the normal background of a line level out is going to have a fair amount of noise because the signal is supposed to be much higher. Did you get a chance to check the two jumpers in the back and make sure they were set the way the book said they should be?

Either that, or try the attenuator cable again. The attenuator will take everything down and then you can turn up signal.
Well I don't know why the attenuator cable didn't work. But the other day one of the Radio Shack guys recommended a 1:1 matching transformer. I tried that, and now it seems to be working a lot better. I haven't had a chance to fully test it from the remote end though.

-Jeff
russellhltn
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#15

Post by russellhltn »

jeffphil wrote:1:1 matching transformer
A 1:1 will provide isolation to take care of ground problems. An impedance matching transformer will bring the volume level up and may make things clearer.
jeffszone
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#16

Post by jeffszone »

RussellHltn wrote:A 1:1 will provide isolation to take care of ground problems. An impedance matching transformer will bring the volume level up and may make things clearer.
I'll guess much of the improvement was because of grounding issue, being as how the video phone doesn't even have a grounded outlet even though everything was hooked through the same power strip.

Are you saying I'd be better of with a different (non 1:1) transformer? How do I know what ratio to get? The one I'm using now is R.S. CAT # 273-1374:

http://www.radioshack.com/product/index ... age=search


-Jeff
russellhltn
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#17

Post by russellhltn »

jeffphil wrote:Are you saying I'd be better of with a different (non 1:1) transformer?
Depends on if you need impedance matching. (low impedance connected to high impedance or the other way around.) Impedance matching will give you high power transfer which results in a higher volume - perhaps even overload requiring attenuation depending on what's going on.

Such transformers are not rated by turns ratio, but by the impedances they are designed to match.
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