"Most computer microphones use the third segment to carry bias power for the microphone." https://en.wikipedia.org/wiki/Microphone_connector
I had thought it was to deliver sound to both sides (rather than left- or right-only) but here we are.
What is bias power?
Some types of mic capsules require a voltage to work
As well as everyone else's answer here about bias power: it could also just be because a 3-pin TRS are cheaper/easier to buy and get assembly tooling for than 2-pin TRS. Economies of scale.
(For a good example of this: 3-axis accelerometers are cheaper than 1-axis and 2-axis ones. Everyone wants 3-axis for mobile phones, drones, human inputs and the like. You're better off buying a 3-axis chip and ignoring the extra channels)
I don't think we can tell from just a picture of the plugs. These are definitely two 3.5mm stereo jacks, colored headphone and mic. Maybe have a look at the manual? Or type the model number into Google? Or use a multimeter and measure the resistance.
So you have two low-quality mics that can distort your discord call twice as effective.
Innovation!
To my layman's understanding (which is not good) it's because of electronic resonance. In other words, how cables can give off/pick up radio waves.
In early radio, this was a problem with microphones picking up signal from radio transmissions, which obviously is unwanted when you're trying to have people hear your voice, and not your voice mixed with competing radio signals.
From what I understand, when it comes to microphones, there is a "hot" a "ground" and a "cold", and the cold is the same signal as the hot but inverted, and apparently this helps prevent picking up radio signals. It is called "balanced," and I'm not sure why other than the inverted signals. So while it looks like a standard stereo cable with three connections, it's apparently actually a standard microphone cable.
There's a lot more radio/electric wizardry going on than that, but that's my understanding of it, as a person who thinks Electricians are real life Wizards. This is based on some cursory internet research, so please anyone with more understanding correct me if I am wrong.
"Balanced" is used for signal transmission with twisted pair cables. The idea is that any interference will get picked up at the same time by both cables, but be of opposite polarity, so the receiver can just average them out to make like the interference never existed.
They don't need to send the same signal inverted, just allow both cables to react in the same way to any interference (maintain the same impedance).
In microphones in particular, there are other two possible uses for a third cable:
- "phantom power", which uses the balanced twisted pair to deliver power to a microphone's built-in preamplifier, which can then send back the sound over the balanced twisted pair (kind of works like PoE)
- "bias power", which is used to prime a transistor connected to an electret microphone in order to overcome its impedance (which can be seen as a kind of preamplifier like with phantom power, but doesn't send the audio back over a balanced pair, and uses lower voltages)
Sorry Jarfil if I'm being nitpicky :|
They don’t need to send the same signal inverted, just allow both cables to react in the same way to any interference (maintain the same impedance).
These are both the same thing, just viewed from different angles. Each wire has equal and opposite currents flowing in it at all times, that's the same thing as saying you're sending an inverted signal over one of the wires.
"phantom power" [...] "bias power"
Stage audio almost universally uses "phantom power" to mean 48V balanced, which is a nice standard meaning for the term, but I'd never claim someone is wrong for claiming they are doing balanced signals + "bias power". It'd raise an eyebrow (have they made a mistake? it's uncommon) but it's still reasonable, I don't think "bias power" specifically refers to only unbalanced configurations.
Albeit my mind might be poisoned by working with badly translated technical documents all of the time :D
Is this better than a normal 4 contact jack without the cold?
"Cold" suggests you're thinking of balanced signalling. You don't have any balanced options with standard headphones and computer PC jacks, everything is unbalanced. Both the 4-connector (TRRS) and 2x3-connector (TRS) variants of your headphone connectors are unbalanced audio.
There might be a difference in crosstalk between the speaker and mic wires (ie signals going to your speakers leaking through the wire insulation and into the mic wires), but it should be inaudible if the cables and headset are designed correctly.
"Better" in terms of less radio interference? I suppose, probably.
I am not an audio engineer. It fascinates me, but most of it is beyond me.
Like how Apple used to be able to send video out of an iPod over a 1/8th connector, using the "sleeve" part as a 5th connector for video.
You're describing balanced/differential signalling. This is used in stage or professional audio (typically over XLR connectors, but not always).
The 3.5mm TRS connectors that the OP has pictured are extremely unlikely to be using balanced signalling. If they did then they would not be compatible with the headphones jacks on computer motherboards or case fronts which follow the AC'97 or Intel HD Audio standards.
It has that wire to output audio on both speakers? That's the green one btw. The pink is for mic input. USB could be for a few different things depending on the features that particularl set has.
Edit: Nvm, thought the question was for a headset, not a microphone. Unless the mic was part of a headset or something. Idk, other comments may have the answer.
The mic is part of the headset, I was wondering why there are 3 contacts on the mic wire unstead if 2 (signal,ground)
