[HaterTot]

Please help me understand.


I always saw audio splitting to be a very simple system. If you split an audio signal into 2, each of the recipients will get 50% of the volume. Also, a device either sends a signal or receives a signal (adds to or subtracts from the system).


In the hopes that I would never have to change my AV receiver input, I tried to join all the signals via a Belkin Rockstar. I've attached an image illustrating what I did. The results were disastrous.


Here are some of my findings. Whenever i say "additive" or "subtractive", i mean with respect to the output volume of my receiver.


1. The Wii input was always great. No matter what combination of things I had running, the Wii input was always purely additive.


2. The xbox360 input was always additive when the console was turned on. When it wasn't, it was highly subtractive.


3. The PC input was both additive and moderately subractive at the same time. Its signal comes through fine, but everything's volume is cut in half.


4. Any mp3 player (tested a sansa clip and an iphone) made EVERY other source decrease by 90%, but itself played loudly.



At this point I'm just really curious. Is anyone able to go through point by point and explain to me why these things happen?

 

[Gizmologist]

"Splitting audio" does not halve the level simply by sending the signal to 2 different units. Each device has its own impedance on the input. Depending on the circuit design this can be a high imedance- 10,000 ohms or higher- or low, 600-2,000. each time you add another connection you are adding to the impedance provided and each device will provide a DC resistance across the output and your perception is that the volume has been lowered.


This is why active mixers are used. each input is isolated or buffered form all the others so there is no degradation in gain or sound quality.


What are you trying to achieve?

 

[Wayne A. Pflughaupt]

Welcome to the Forum, Hater!


Here’s the problem. You’re not splitting any signals. Splitting means dividing an output so that it can go to two different inputs. What you’re doing is combining the signals of multiple outputs down to a single input.


Even worse, it looks like you’re combining line level signals with probably different impedances with a high-level amplified signal. That would be the MP-3 player. Behind the headphone jack is a low-powered amplifier, since its purpose is driving speakers.


You need to connect all this gear to independent inputs on the AV receiver.


Regards,

Wayne A. Pflughaupt

 

[MichaelJHuman]

If you combine two line level audio signals by simply connecting two interconnects together, voltages will sum, I believe (this is easy to understand, if you think of how batteries work in series.)


Seems like you could run into issues with the output from one device feeding back to the output circuits of the other device, but my knowledge is too minimal to explain what happens there.


If on the other hand, you split the output of one device to feed two or more inputs, you would expect very little change in "volume." (signal level). If you apply ohm's law and a few other facts, you can see this.


Take a simple circuit with a 9V battery connected to two 100 ohm resistors in parallel. We know that the total resistance in parallel is 50 ohms (this is obvious in this case, because putting two equal resistors in parallel decreases resistance by half as there's twice the "area" for current to flow.) So .18 amps flows through the circuit (9 / 50 = .18)


We also know that currents must sum at every juncture. This is intuitive. As both "sides" of out parallel circuit have equal resistance, current will flow through each side equally, so half the current must flow through each side. Because .18 amps flows in, and divides equally, then the current sums back to .18 amps where the parallel circuit becomes a single lead again.


So we know due to ohm's law that 9 Volts potential present at each resistor. More precisely, that the voltage drop over each 100 ohm resistor is 9 Volts (100 * .09 = 9.)


In other words, voltage is the same when "split." Current on the other hand will "split". For line level connections, voltage is what matters, because "information" transfer is via voltage. This is not universally true for all kinds of connections, which is why you will see talk about matching impedances in some contexts, for maximum power transfer (and minimal reflections back to the output.)

 

[razr67]



Quote:
If you combine two line level audio signals by simply connecting two interconnects together, voltages will sum, I believe (this is easy to understand, if you think of how batteries work in series.)

Batteries in series, and audio sources in parallel are not the same thing. The source impedance is the determining factor.

Quote:
Seems like you could run into issues with the output from one device feeding back to the output circuits of the other device, but my knowledge is too minimal to explain what happens there.

A source, with a zero volt output, such as during audio silence, will short the other source, since it's effectively at ground.

 

[MichaelJHuman]

Agreed, my battery analogty was flawed. I know people have connected two sources together with a Y cable or at least said they did. But as you say, it's probably not recommended.

 

[Speedskater]

I think that this Rane paper covers the subject:


Why Not Wye?
http://www.rane.com/note109.html

 

[ChrisWiggles]



Quote:
In the hopes that I would never have to change my AV receiver input, I tried to join all the signals via a Belkin Rockstar. I've attached an image illustrating what I did. The results were disastrous.

Good lord. Obviously disastrous.


Connect them to unique inputs.


If you wanted to combine them all together, you would need to buy a mixer, but clearly that's not what you're really trying to achieve.


What you are doing is completely incorrect, and a total misuse of the splitter as a "combiner", which is a terrible idea and won't work right, as you discovered, and can damage your equipment.

 

[Gizmologist]

The old school method for combining 2 sources or 2 channels of 1 source together is to use a 47k resistor in series with each hot leg (center conductor) of the sources as they feed into the amp input. This offers some isolation and minimizes the loading effect of multiple source connections.