Plugs and jacks are usually used for transmittals of line-levels (0.775 volts). Their major applications are the connections of instruments like guitars, keyboards, headphones, ...

Plugs and jacks are used for microphone signals if you handle them with a patch-panel. Optionally they are also used for low power speaker applications.

There are two main groups of plugs and jacks:

• 2 pole connectors (TIP & SLEEVE)
• 3 pole connectors (TIP, RING & SLEEVE)

In the nonprofessional HiFi-area it’s common to use the 3 pole connector for stereo signals (headphones) and the 2 pole connector for mono signals.

In the professional broadcast and audio industry the 2 pole connector is used in combination with unbalanced cables for short and interference insensitive transmittals (guitar cable).

For more sensitive applications like digital transmissions or longer lines it is the custom to use 3 pole connectors together with balanced cables (to avoid EMI - electromagnetic interference), but it’s still a mono signal (balanced mono signal).