What Is Aux? The Auxiliary Connection Explained
Aux is short for auxiliary, and in consumer audio it means a line level input that accepts whatever you connect to it.
Quick Answer
An aux input is a line level analogue input, almost always a 3.5 mm socket. It accepts a stereo signal from a phone, computer or player and passes it to the amplifier inside the device. The plug is normally a three conductor TRS type: tip for left, ring for right and sleeve for ground. A four conductor version adds a microphone connection.
The Connector and Its Wiring
| Plug | Bands | Carries |
|---|---|---|
| TS | Two | Mono signal and ground |
| TRS | Three | Stereo left and right plus ground |
| TRRS | Four | Stereo plus microphone or video |
| Adapted to RCA | Three into two plugs | Stereo pair for older equipment |
Where Aux Is Still Useful
Cars without wireless
Older head units often have an aux socket and nothing else.
Reliability
No pairing, no codec, no battery. It either works or the cable is faulty.
Latency
There is none, which matters for video work and some games.
Compatibility
Any device with an analogue output can use it.
Levels and Practical Notes
- Set the source volume around two thirds and control the level downstream.
- Too low a source volume raises hiss from the amplifier.
- Too high can clip the input on the receiving device.
- Hum that appears only while charging is a ground loop, not an aux fault.
Using It Well
- Identify which side is the input, not an output.
- Check whether the socket is 3.5 mm or 6.35 mm.
- Use a screened cable to reduce interference.
- Keep the cable reasonably short.
- Set levels as described above before adjusting tone controls.
Real-World Applications
- Phone into a car stereo.
- Computer into powered speakers.
- Portable player into a home amplifier.
- Backup connection when wireless is unreliable.
Related Guides
For adapters, read USB-C to 3.5mm adapter. For connectors, see 3.5mm to jack. For professional connections, start with 3.5mm to XLR cable.
FAQ
Is aux the same as Bluetooth?
No. Aux is a wired analogue connection. Bluetooth is digital and wireless.
Does aux carry better sound?
It carries whatever the source produces, with no codec or compression added.
What if my phone has no headphone socket?
Use a matching adapter, such as USB-C or Lightning to 3.5 mm.
Why does one channel go silent?
Usually a plug not fully inserted or a broken conductor in the cable.