Shelves of audio equipment come with a variety of sockets, and it is not always obvious which cable goes where. This guide identifies the most common consumer audio connectors, explains what each is for, and notes which ones can be safely swapped and which cannot.
3.5 mm TRS (the “aux” or headphone jack)
The 3.5 mm connector — sometimes called a mini-jack or aux input — is the small round plug used on headphones, smartphones, and portable players. “TRS” stands for Tip-Ring-Sleeve, which describes the three conductive sections. On a stereo headphone cable, tip carries the left channel, ring carries the right, and sleeve is common ground.
The same connector is used as an aux input on speakers, car stereos, and amplifiers. When used as an input, the signal level is “line level” — the same nominal level as other consumer audio sources. The connector itself is identical whether carrying a headphone output or a line output; the difference is the signal level, not the plug.
RCA (phono connectors)
RCA connectors are the paired red-and-white plugs common on home audio equipment, televisions, and older video equipment. Each carries a single channel: by convention, red is the right channel and white (or black) is the left. They carry unbalanced line-level audio.
RCA and 3.5 mm TRS carry the same type of signal (unbalanced, line level) and inexpensive adapters exist to convert between them. The adapter itself introduces no quality loss — both are unbalanced connections at the same nominal level.
6.35 mm TRS (quarter-inch jack)
The larger quarter-inch jack appears on musical instruments, amplifiers, mixing desks, and professional headphones. It works on the same principle as the 3.5 mm version. A quarter-inch jack in a guitar amplifier input expects an instrument-level signal (weaker than line level). Plugging a line-level source directly into an instrument input can cause distortion.
What you can and cannot substitute
- 3.5 mm to RCA: works. Both are unbalanced line-level. An adapter is reliable.
- RCA to a line-level input: works. This is the intended use.
- Headphone output to line input: usually works, but a headphone output can be at a higher signal level than a line input expects. Turn volume down before connecting and raise it gradually to check for distortion.
- Instrument output to line input: the signal will be weaker than expected. Use a DI box or instrument-level input instead.
Speaker cables are not audio cables
Speaker cables carry power from an amplifier to a speaker driver. They are at a different signal level entirely and should not be plugged into line-level inputs. Speaker outputs on an amplifier are not interchangeable with line outputs.
Frequently asked questions
Why do my RCA cables have different colours for video equipment?
The same RCA connector was used for composite video (yellow) and component video (red, green, blue) as well as audio. The physical connector is identical; the colour coding tells you what signal each carries. Do not plug a composite video cable into an audio input expecting audio — it will not work because the source equipment sends a video signal, not audio.
Does a more expensive aux cable sound better?
For short cable runs inside a home, the answer is almost always no. An undamaged cable with good connectors that make reliable contact will perform identically to a more expensive one. Shielding matters more in electrically noisy environments. Very long runs (several metres) can benefit from better shielding, but for desk-length connections a standard cable is sufficient.