Audio processing is often called audio signal processing to differentiate the audio processing performed by machines from that performed by the biological auditory system. The mechanical processing of audio signals has been in use from the 1920s, since the beginnings of radio broadcasting. Audio processing is most often used to clean up or enhance an audio signal before it is transmitted.
There are two types of audio processing. Analog processing was the first and involves converting a sound wave into an electrical signal. Once it is in electrical form, the signal can be manipulated. The electrical signal used in analog devices closely resembles a sound wave, which allows the sound to be processed with the least amount of distortion.
In digital audio processing, an audio signal is converted into digital information, often binary code, which can be interpreted by a computer. A digital signal changes the nature of sound from a continuous wave into discrete packages of information. These can be reassembled in such a way that the human ear cannot tell the difference between sound that has been digitally processed and that which has not. Digital audio processing is more popular than analog processing because it allows for greater control of the audio signal.
There are a number of ways that audio processing is often used. Enhancement of sound is one of the most frequently used forms. It can include boosting the volume of signal and cleaning up background noise. Additionally, sound from different tracks can be mixed and sound effects added in.
Once a sound undergoes its initial processing, it is usually converted to a digital or analog signal again before it is transmitted to a radio receiver, television, cell phone, or any other device capable of receiving and playing audio signals. Once the signal reaches its final destination, it often undergoes other forms of audio processing before it is played for the listener. A theatre system with multiple speakers, for example, needs to process the sound in order to spilt it into multiple channels. It is also common for an audio signal to have noise reduction and a signal boost performed just before it is played.