Sound is the most important feature that differentiates radio from other media.

• Sound is absent in printed media (unless activated in the reader's mind, in which case the "sound" is wholly subjective to the reader).
• Sound is of secondary importance in visual media, where pictorial images dominate: the primary function of sound in visual media is to reinforce the illusion of reality.
• On radio, by contrast, sound is the exclusive channel for communication.

Let us consider three distinct aspects of radio sound:

• voice;
• acoustic effects;
• music.

Insofar as radio producers look for writing that is potentially exciting for radio, writers should not expect their work to be given serious consideration unless it exploits at least some of radio's potential for exciting sound.

VOICE

Radio writers have exceptional control over characters' voices and the sounds they make.

• Whilst voices are important in visual media, they are of secondary importance compared with appearance and facial expression.
• Whereas radio writers' ideas are usually carried through, film and television writers often find their ideas transformed at the whim of producers, directors or actors who are not obliged to learn their lines properly.

Because the voice is of paramount importance in radio, the potential for creative use of language on radio is no less than in books. Arguably, the evocative power of the voice is greater on radio by virtue of the potential for adding acoustic subtext that is inaccessible to writers of books. For example, whereas the irony of an out-of-character statement by a character in a book may require paragraphs of explanation, the same sense of irony may be communicated and understood instantly on radio through vocal inflection.

Radio writers should also bear in mind that the path from first reading to (recorded) performance is much shorter than in, say, theatre, and that their intentions must accordingly be more clearly communicated to radio actors than they need be to theatre actors.

In theatre, directors and actors spend many hours analysing characters and bringing their voices to life. Radio budgets seldom allow this: once the piece is accepted for production, it is more likely than not that the writer's intentions will be taken largely at face value .

• If the writer intends particular accents, they should be specified.
• If lines are to be spoken in a certain way, the actor must be told in concise terms and at the appropriate moment in the script.

In short, when creating radio voices, writers must give consideration to the widest possible gamut of aspects of voice (evocative language, accent, emotional range, etc) and communicate their intentions clearly and directly to the actors through the script.

ACOUSTIC EFFECTS

The impact of acoustic effects on radio listeners is so subtle that we are often unaware of them.

Arguably, the most immediate acoustic effect is the sense of being indoors or out. Whilst most listeners could not begin to explain the science of ambient sound, our sense of place, as discerned through sound, is nevertheless acute.

Our sense of time and place are greatly amplified by the use of additional acoustic effects. For example, an exterior acoustic coupled with the sounds of a man shouting "Whoa!" and horses hooves coming to a halt amid a splashing of water, conjures up in a split second a complex image that might require considerable explanation on the part of an author.

Furthermore, the image presented in that short burst of sound opens up a rich array of ambiguities that might be immediately stifled by more the blatant imagery that is characteristic of visual media.

In other words, acoustic effects offer the radio writer freedom not only from the need for descriptive narrative (which inhibits immediacy) but also from the imagination-deadening effect of pre-packaged visual images.

The over-use of acoustic effects is certainly a cause of annoyance to many listeners, and must be avoided. Conversely, the would-be radio writer should not expect his/her work to be considered by a producer unless it has been plainly conceived for radio: in other words, unless the script clearly exploits radio's unique potential for communication through acoustic effects or, at the very least, offers minimal directions for the sound technician who will certainly be a part of the production team.

MUSIC

Insofar as music is an acoustic effect, it has already been discussed (by inference) in the paragraphs above. A case in point is "iconic" music, that is to say familiar pieces of music that are particularly evocative of time and place in the public consciousness. Radio producers often use iconic music, and especially pop music from the 1960s onwards, for the exclusive purpose of suggesting time and/or place.

When using iconic music in their work, radio writers should be conscious of its tendency to overpower all else in the soundscape: it makes poor background music.

For the most part, however, music is more subtle, insofar as it works primarily and inscrutably at the emotional level. Being, in effect, meaningless at the level of cognitive thinking, music fulfils several roles that more concrete acoustic effects cannot:

• Background music can be used to deliver emotional impact that lies beyond the reach of ordinary acoustic effects (such as the music that heightens attentiveness and makes the listener anticipate the terrible thing that is surely about to occur).
• Foreground music can be used to tell part of the story without words: for example, the action of a play about the onset of a debilitating disease might be complemented by perfect piano music at the start of the play, wrong notes in the middle of the play and finally a complete breakdown.
• Music may be particularly effective in effecting radical scene changes rapidly (such as the music on the Light Programme that suggested Paul Temple's journey from London to continental Europe as he embarked on his latest crime-solving adventure).