The heart of a radio station, for presenters, is the mixing desk, often shortened to simply “the mixer”. It is also variously called a console or a board in places. It controls the various programme sources and adds their audio together before sending them to the radio station's real heart, the racks.
Mixers are generally problem free until a presenter decides to feed them with a drink or other substances. Rotary faders were most 'presenter proof' as there was little room for the tea, coffee or coke to get in, and being mounted almost vertically there was less chance of a heavy pile of vinyl or anything else being dropped on them.
Since horizontally-mounted linear faders became common-place in the 1970s, the mixing desk has become much more vulnerable. Some studios introduced a firm 'no liquids' ban but the desk is still the most vulnerable item of equipment in a studio.
Digital Mixing Console
The move to digital mixing, where the desk is simply controlling a remote piece of audio equipment in a racks room elsewhere, is a tremendous boost to reliability.
At its simplest a mixing desk is just a set of controls that will mix together the outputs of your sound sources. The complexity of the mixing console needed will depend on the type of programme you intend having, in particular how many sources will you use, and how much control will the operator have over the playout process.
The mixing desks seen in recording studios will often have many channels into which the sources can be fed. 64 and 128 channels is becoming standard, and each of those channels can have up to a dozen separate controls with which to set various equalisation parameters, sending to effects such as reverb' and so on. A recording studio desk however is neither necessary nor indeed optimum for radio broadcast use. The main need in a radio studio is for 'controllability'.
The mixer is the heart of a radio station and as such is not simply a tool for varying the sound levels or EQ. It should also be the place where all the various programme sources are controlled; switching sources in an out of circuits, remote starting items and so on. Sources need to be 'auditioned' or cued up ready for airing, some need to be sent to external processors, or to be recorded. The needs of radio station mixer are many and various and quite unique.
At the very least, a radio mixing desk needs to have a method of cueing, or auditioning a source, without putting it into the programme chain (live on the air). Cue circuits (usually a separate channel) enable the precise start point of the source's programme material to be found, and then handed to a remote start control on the desk. This is often included into the main fader, so that when it is activated it automatically cues the item for 'instant start'. This is regarded as 'slick presentation' - a seamless playout without embarrassing gaps between items.