Questions about input cable "splitting".

[MrMungus]

1. Can s-video cables be split so that, for example, I could send a VCRs output to two computers at the same time (say, if I wanted to capture on one to DV AVI and the other directly to MPEG-2)? How much signal loss is involved and is it significant if you're only splitting it once?

2. I know composite cables for a video signal can be split but I have the same question: how much signal loss is involved?

3. I know composite cables for an audio signal can be split; again, is the loss significant enough on audio (I'd think splitting an audio composite cable would have less of an impact on quality than splitting a composite video cable).

So the real question on all of these (individually) is: Is the loss significant enough to be a concern?

Thoughts/experiences?

[snafu099]

This is not a tech reply, just my experience/use.

I use composte rca cables for audio & vid, splitting them from vcr/dvd to seperate composite input monitor and usb ADS cap device. No quality loss that I can tell

[Richard_G]

You can't get something for nothing. A standard composite video signal is 1 volt peak to peak. Splitting it will give you only 0.5 volt peak to peak on each leg (assuming identical input impedance on both devices). This will show itself as a loss of brightness in the image at each capture/display device.

The same goes for audio. Only half the signal will arrive at each input so the level will be lower resulting in an decreased signal to noise ratio. Or in laymans terms, more hiss on the audio.

[MrMungus]

You can't get something for nothing. A standard composite video signal is 1 volt peak to peak. Splitting it will give you only 0.5 volt peak to peak on each leg (assuming identical input impedance on both devices). This will show itself as a loss of brightness in the image at each capture/display device.

The same goes for audio. Only half the signal will arrive at each input so the level will be lower resulting in an decreased signal to noise ratio. Or in laymans terms, more hiss on the audio.

Is the same true for s-video?

[Richard_G]

Yup!!

[FOO]

I don't know about that. (actually I do )
If you use an official impedance matching transformer
splitter , each side goes down 3dB to 0.707 V
If you just run 2 outputs in parallel , I would calculate 0.333 V
edit: oops how about 0.666V

and if the device has an AGC you will notice only a noise increase

[ZippyP.]

A standard composite video signal is 1 volt peak to peak. Splitting it will give you only 0.5 volt peak to peak on each leg (assuming identical input impedance on both devices).

If you simply "split" the signal with a Y connector then the loads will be in parallel, not series. Although the load is increasing (load impedance is dropping) it doesn't necessarily mean that the voltage will drop in half. As long as the output device can handle it you're probably OK.

[FOO]

Although the load is increasing (load impedance is dropping) it doesn't necessarily mean that the voltage will drop in half

Why not ? I think you are guessing . What's the number ?

[Ste]

They got a good explaination here:

http://www.s-video.com/svideosplitter.html

[FOO]

Sorry. I fail to see any explanation at all.
Perhaps you could read it and explain it to us

[ZippyP.]

What's the number ?

how about 0.666V

:P

[ZippyP.]

Seems to me the explanation is when you use a Y-connector that the signal is degraded and some devices can handle it and some can't.

[Ste]

Yeah, it's at the bottom of the page. It explains the consequences of splitting an s-video cable passively.

[lacywest]

Ohm's Law:

Ohm's Law says that there is a relationship between these three factors. So if you know two of the values you can easily work out the third one.

V = I x R
I = V / R
R = V / I

If you know the current and resistance and want to calculate the voltage, you use the first equation. If you know the voltage and resistance and want to calculate the current, you use the second equation. Lastly, if you know the voltage and current and want to calculate the resistance, you use the third equation.

http://www.purchon.co.uk/radio/ohmslaw.html


AMPS= ... WATTS÷VOLTS ... I = P ÷ E

Watts = IxE

Two 8 Ohm speakers connected in parallel becomes 4 Ohms

This means the amplier will want to deliver more current to feed the lower impedence ... aka ... resistence.

Voltage stays the same. In a ideal amplifier.

So ... 1 volt dropping to half of a volt ... no is the answer.

But ... there could be a impedence mismatch or the amplifier is not able to produce twice the amount of current to more than one load.

Now take two 8 ohm speakers and hook them up in series ... well 8 + 8 is 16. The current will be reduced ... more resistance.

Think of a large dam holding a billion gallons of water. Their is your potential ... called voltage.

You now connect a pipe to drain the dam of water ... the flow of current [water] ... is based on the diameter of the pipe [resistance]

The more water that is in the dam ... higher voltage ... creates more pressure.

[FOO]

This is more complicated than you may think.
The only reason I gave my answer is that I ignored transmission line
effects because the wavelength of a 4 MHz video signal is
much longer than any video patch cords you may have.
If that were not the case the actual geometry of the cable would
have to be known to figure it out.

Where the split connection is
How long is each cable section etc.

[Alan69]

Not only is the input impedance on each 75 ohms, but the output sourcing is designed to drive 75 ohms. I think it was that the voltage doesn't actually go by half, but when you take the new voltage and the new current through each 75 ohm resistor, you get 1/2 power in each.


BUT: These resistors are for matching transmission lines. BIG solution:


DO NOT SPLIT the lines. Instead, use it as a proper transmission line, just like SCSI. OUTPUT, VCR1, VCR2. Make VCR 1 your cheap VCR. Open VCR1 and cut it's 75 ohm resistors on the video and audio input lines. Signal now goes out the output, down the line to VCR1, and into VCR2's input and terminating resistors so no reflections. And VCR1's actual input buffers will be high impedance, when you cut the resistors it will see clean signal without unneeded loading of the line. It is just like chaining 7 SCSI devices works fine, with only two terminators at each end. A split stinks, chaining works great. At one time the 75 ohm load was actually driving something, but these days it's all high impedance inputs with 75 ohm resistors only for line termination.

Most really still work ok with a split, but chaining should bring it back to perfect. Simple amp circuits work too, but snipping the resistors on a cheap unit is fast and easy. It will no longer work well not in a chain though, unless you add the 75 ohm resistors back on the outside of the cable. Really would be nice if they'd move into the 90's and take the resistors out and put them in the cable ends, and make multidrop cables..

Alan

[FOO]

but when you take the new voltage and the new current through each 75 ohm resistor, you get 1/2 power in each.

Not true

[MrMungus]

Seems to me the explanation is when you use a Y-connector that the signal is degraded and some devices can handle it and some can't.

hehe

So...is it noticable or not?

I guess I should just test it to find out.

[lacywest]

Seems to me the explanation is when you use a Y-connector that the signal is degraded and some devices can handle it and some can't.

hehe

So...is it noticable or not?

I guess I should just test it to find out.

yes ... but how ?? ... cut open the cable and attach some wires??

Serious ... let us know ... I have a need too for spliting my S-VHS cable out to another connection.

It's a regular rat's nest ... next to my computer and my 3 VCRs and my Panasonic DVD Recorder. LOL

[Gazorgan]

Come on guys: RMS or P-P ? 1 Volt P-P is .707 RMS.

You can split S-Video, but the resulting voltage drop can introduce 'sparkles' and reduce color levels (red being the most sensitive color).

You can get 'Amplifiers' for S-Video , Audio Line level, and Composite Video that amplify while splitting. You have an input then 2-4 outputs at the required level. Pretty cheap at Radio Shack.

[FOO]

Come on guys: RMS or P-P ? 1 Volt P-P is .707 RMS.

You have no idea what you are talking about

[MrMungus]

Seems to me the explanation is when you use a Y-connector that the signal is degraded and some devices can handle it and some can't.

hehe

So...is it noticable or not?

I guess I should just test it to find out.

yes ... but how ?? ... cut open the cable and attach some wires??

Serious ... let us know ... I have a need too for spliting my S-VHS cable out to another connection.

It's a regular rat's nest ... next to my computer and my 3 VCRs and my Panasonic DVD Recorder. LOL

I'd just do a capture using an unsplit cable and compare the quality of the audio and video to that of a split cable setup. Someone posted a link earlier referring to splitting s-video cables. Scroll down on that page for useful info about splitting s-video.