Audio effects can be of two kinds: The ones that are actually recorded from a source – a car passing, say, or a baby crying – and the kind that are generated artificially to change the audio quality of a recording or emphasize something (a whistle or bloop or thweep, for instance).
Properly used, effects can add a whole new dimension to recorded sound. Effects can make advertisements more appealing; dramas more dramatic; and jingles ear catching. Nearly all computer-based digital-editing systems now come equipped with a toolbox of effects – but it is often simplest to record the kind of sounds we want, unless we want something quite unnatural which can only be created artificially.
Of the many effects that one might use in radio work, the most common and popular are as follows:
1. Reverberation
Reverberation (or reverb) is the natural reflection of sound from walls and structures around us, which give a voice its ‘presence’ in an enclosed space. These reflections reach us so quickly after the original sound is made that we don’t consciously perceive them as being separate from the main sound – but we can and do notice when they aren’t there. (This is why a padded room or an acoustically treated studio floor, where reverb has been deliberately reduced through various techniques, sounds ‘dead’ to us, as if our voice has been swallowed up by the room.)
For audio recording purposes, we always try to record ‘clean’ sound – that is, sound without reverberations in a controlled studio environment. Later, during post-production, we add the ‘reflections’ electronically, to the exact degree that we require. Doing this well is an art, and calls for sharp ears and an understanding of what real reverb sounds like. Done properly, it can create the impression of a real room of a specific dimension.
2. Echo
When the reflection of the original sound reaches us after a distinct delay, we perceive the reflected sound as an echo. In electronic terms, we can add echo the same way we add reverb, but by increasing the return time.
3. Delay
Along with echo and reverb, we can also electronically create multiple reflections, and alter the duration and volume at which each of these echoes return after the original sound. This is achieved by using the delay effect controls. If the delay effect is used in combination with the pan control (see below), this can create spatial effects in stereo.
4. Modulation
Modulating the delay time creates modulation effects. If we use a low frequency oscillator to generate a signal that varies the delay time in accordance with the frequency of the oscillator signal we can create a chorus effect, like two or more voices singing the same part, but with slight differences in timing and tuning.
Using different length delays and different modulating frequencies can also create effects like:
Phasing: Very short delay time and mixing the delayed sound with the original creates a slightly flatter and ‘treated’ effect;
Flanging: A longer delay and feedback creates the effect that we hear when a guitar string is stretched sharply in the middle of a note;
Vibrato: When only the delayed sound is used, with a slight change in pitch, to create a wavering sound that is more tremulous than the original.
5. Pitch shifting
Pitch is a measure of the overall combination of frequencies in a sound or voice. (Hence: "She has a high-pitched voice" – that is, a voice where the shrill notes and higher frequencies predominate.) Before the advent of modern effects processors, pitch shifting was achieved by speeding up or slowing down the recording during playback – the former increased the pitch, and the latter decreased it. Unfortunately this technique also changed the overall length of the audio. Modern effects processors can pitch shift the sound – make it shriller or more bassy – without changing the speed of the audio.
6. Time stretching
Another sound effect that is possible with modern effects processors is the time stretch, where the length of the audio can be changed without affecting the pitch of the audio.
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