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There are many different types of audio connectors, plugs and sockets. Some are found commonly on domestic equipment, whilst other types tend to be only included on professional gear.
Leads come in two basic forms – ‘balanced’ and ‘unbalanced’. This refers to the way the audio leads are wired and connected to equipment, in terms of how electromagnetic and radio frequency interference is handled. Interference can come from all kinds of sources such as fluorescent lighting, two way radios, electric motors, arc welders and so on.
Unbalanced leads and plugs/sockets are prone to interference and are not suitable for long lengths. Typically an unbalanced lead has a central core wire, surrounded by a sheath of braided wire. As both core and sheath are used for the audio signal, any interference picked up on the sheath will get to the audio equipment as unwanted noise. Apart from guitar leads, unbalanced leads are not usually used for professional applications. Plugs on unbalanced leads are usually 1/4″, 3.5mm or RCA types.
Examples: non-professional microphones, headphone leads, home stereo and TV audio leads, guitar/instrument leads.
Balanced leads typically have 2 cores for the audio signal, surrounded by a wire braided sheath. Any interference is shielded by the sheath and sent to the audio equipment’s earth. The ‘clean’ audio Audio signal travels along the two core wires, thus protected by the sheath and insulated from interference.
Balanced leads are more suited for long lengths and are commonly used for connecting professional microphones. Balanced lead connectors are often 3-pin types known as XLR plugs/sockets.
XLR connectors are sometimes referred to as ‘Cannon’ (not to be confused with Canon cameras) or ‘Amphenol’, so called after two large manufacturers of these types of connectors.
Condenser type microphones need power to operate. This can be either from a built in battery, or from ‘phantom power’ sent along the microphone lead from a suitably equipped audio mixer or camera. ‘Phantom power’ requires a balanced lead with XLR connectors, and is therefore not found on domestic equipment.
Most handycams and DSLR cameras capable of video do not have XLR connectors. Instead they usually have 3.5mm unbalanced sockets, so professional quality microphones can not be used without a special adapter. Pro video cameras usually have XLR audio connectors and often include a phantom power supply (typically 48 volts).
A good solution for connecting professional microphones to a DSLR camera is to use an adapter called a balun (bal-un), such as the Beachtek DXA-SLR Pro.
This electronic box of tricks mounts on a tripod and the camera mounts on top of the box. The Beachtek balun has two XLR sockets for connecting professional quality microphones, a headphone socket and a short lead with a 3.5mm plug for connecting the output to the camera’s external microphone input socket. Although the output lead is unbalanced, being short, the possibility of interference is reduced. The two XLR connectors also offer a choice of 12v or 48v phantom power.
More than being a simple adapter, the Beachtek balun includes a two-channel audio mixer and sound level meters. The circuitry inside also tricks auto-only sound level cameras into behaving as if they have manual levels.
More info here.
Below: another Beachtek balun model showing camera mounting and audio connection.