Splitting an analog microphone signal

I have a very basic headet analog microphone setup, with two 3,5mm plug connectors, one for the phones and other for microphone. It is plugged to a simple USB audio interface which has three inputs - mic, phone and line-level output (speakers out).

I need the microphone output signal to go into two computers simultaneously.

Qa: Is it possible to somehow “split” the microphone signal to achieve this, or will the signal level be too low without amplification?

Qb: Is it possible to set up a USB audio interface (any) to directly transmit mic signal live out via the line-level output? This way I could connect the USB line-level output to the second computer audio in and achieve the same result.

<<<Is it possible to somehow “split” the microphone signal to achieve this, >>>

No, but not for that reason. You do not have a “microphone.” You have a computer microphone which is sending its tiny voice signal to the computer, but it’s also getting battery from the computer to run itself.

It’s the bottom illustration here.


So they’re married. The split would have to block one of the two computer batteries from the “Y” split, but still let the sound through.

You could try it anyway. Radio Shack sells six inch long headphone splitter “Y” cables which would work. The voice volume would go down 6dB which Effect > Amplify should be able to deal with no problem in Audacity post production. I don’t expect it to work, but it might.

You can also do this with electronic components and tools from Radio Shack, but every time I suggest this, people look at me like I have palm trees growing out of my head.

What’s “soldering?”

The last piece of this can’t be done either, also for a wacky reason. You can’t put computers in daisy-chain one after the other for sound because of delay problems. Each computer has to think about the sound for a bit and each time it does that, it comes out late. That’s one of the serious problems with singing a song to yourself. The headphone feeds are not in real time. They’re late and trying to sing that way will drive you crazy.

If you’re already crazy, that might not bother you.


Thanks Koz. What this setup is for is not recording as such.

It is for a flight simulation purpose, where on the main computer I have a program constantly listening to audio commands. On the second computer a program that is used to communicate with online air traffic control. That is why I need to split the signal because I can’t use two microphones. If that sounds geeky, it is!

I’ll try the Y-cable solution. Volume attenuation may or may not be a problem.

For the delay problem, it may not be a problem at all as I would not hear the voice myself and the person on the other end would not know the difference. I assume the delay would not be even half a second. If only I knew how to try the chain…

You can’t split USB because USB is a bi-directional communications channel. It’s not a garden hose you can easily split into two hoses.

Is the second computer a deskside with a full audio card? If so, you can split your headphone signal with a “Y” cable and plug the second feed into the Line-In of the second computer. If the second computer is a Windows laptop, that’s not going to work. Most of them do not have High-Level, Stereo Line-In.

Is there an Audacity anywhere in this process?


I wouldn’t recommend it. As you say, there’s DC voltage on the microphone sockets. Usually it’s difficult to short the DC voltage to the microphone input because of the contact arrangement, but with a splitter cable it is probably quite easy. My guess is that there is a relatively high chance of destroying one of the microphone inputs (a greater chance than I would want to take).


The intention is not to “split the USB cable”. Again, I have a separate headset with analogue connectors, which I plug into a USB interface connected to the primary computer.

If the mic signal is to be “split” it will be before the USB interface. But reading stevethefiddle’s reply I’ll consider it a bit more.

My best (and only) bet seems to be somehow looping back the signal → that goes into the USB interface via mic input → comes back via the USB interface speaker output → to the second computer’s line in. What do you think?

Splitting microphone signals is a very long way away from ideal, but I guess you’re looking for a cheap and cheerful solution without blowing anything up, but quality is a low priority?

Are you any good at electronic DIY?
If you’re using two cheap USB microphone inputs, there’s a fairly safe way that you can do this but it involves either making a splitter lead, or modifying one.
Typical headset microphones (and computer microphones in general) use 3 connections on a “stereo” mini-jack connector. It’s not really stereo, it’s mono. 2 of the connections are for the microphone signal and one is to supply a voltage to power the microphone (these type of microphones need to be powered).

On the mini-jack, there is a “tip” (1), then a “ring” (2), then the main sleeve (3). These are the 3 connections.

Tip (1) = signal
Ring (2) = +5V
Sleeve (3) = ground.

Make or adapt a splitter cable so that all three pins are connected on one of the mini-jack plugs, but only the tip and sleeve (1 and 3) are connected on the other.
Connect the microphone with the splitter cable to the USB microphone inputs BEFORE you plug them into the computers and tape them in place as a reminder not to unplug them while it is powered up.


Which puts you right back into Radio Shack Soldering and palm trees growing out of your head.

About this “I can’t use two microphones” thing. Why not? You put on the regular headset and then twist-tie or sticky-tape one of these on the headset microphone boom.


That will easily plug into the second computer whether it’s a laptop or not and has the additional advantage that you can set levels independently between the two microphones. It sure has a lot better chance of succeeding compared to what you’re trying to do.


Thanks all.

Yeah, soldering bits and pieces together in this case might not be worth the trouble. It’s an option though, thanks for that.

As for the second microphone option, that’s not a bad idea either I guess, if the microphone is really small and light enough to easily clamp or tape to the boom of the headset. I’ve just always had my doubts about the sound quality of cheapo tieclip microphones. Especially as the sound is further garbled and distorted by the peer-to-peer communication method used in this context, I’m concerned I might be “unreadable” at the other end.

Worth a try though. Certainly to try that is a lot cheaper that having to buy a top-end multicore processor to run all these programs on one computer.

We use those for theatrical presentations, live training sessions, and videoconferences. It’s not a crappy microphone unless the battery is weak, and those go for six months. You pull the wind screen and tie clip off and you’re left with an 1/8" microphone capsule and thin lead wire. The second computer needs to have the ability to do a +20dB microphone boost. Not all sound cards have that and it’s required for this mic.