Companding: Enhancing Audio Signals for Clearer Sound

Companding: Enhancing Audio Signals for Clearer Sound

Introduction to Companding

Companding is a technique that is widely used in audio processing to reduce the dynamic range of audio signals. This technique involves the use of compressors and expanders, collectively known as companders. The primary goal of companding is to make quiet signals louder and noise signals softer, thereby improving the overall clarity and quality of the audio.

How Companding Works

In a typical audio recording situation, a compander is employed to compress the dynamic range of the signal. At a specific point, the signal is reduced in volume. For example, if the loudness of the signal increases by two decibels, the output signal will only increase by one decibel. This is a basic example of compression. However, in practical applications, makeup gain is often used to compensate for the reduced volume, making the entire signal louder.

By using makeup gain, the quietest signals become about twice as loud. This is particularly useful for noise reduction, especially when recording to tape. Tape, being a magnetic storage system, has inherent noise that can be controlled. This noise is referred to as the signal-to-noise ratio. By compressing and then boosting the signal, the quietest sounds in the signal become twice as loud, thereby increasing the signal-to-noise ratio. When the audio is played back, an expander is used to reverse the compression process, making the tape hiss and other noises half as loud as they were during recording.

Applications of Companding

Companding is not limited to just recording and playback. It is also used in situations where signals are transmitted over airwaves to reduce the amount of noise that creeps in. These systems are known as companding systems.

Live Recording Situations and Companders

In live recording situations, the use of a compander can be particularly advantageous. When using a compressor with makeup gain during a live session, the surrounding sounds that are below the threshold of the subject's voice are inadvertently boosted. This can be problematic and can lead to harsh sounds. To solve this issue, an all-in-one companding unit can be used. The expander portion of the compander can be set to activate below a certain level. As the sounds get quieter, the compander pushes them further down. This gradual reduction in loudness is more natural and avoids the abrupt cut-off that can be harsh on the human ear.

Conclusion

Companding is a powerful tool in the audio engineer's toolkit, offering improvements in signal-to-noise ratio and the overall clarity of the audio signal. Whether you are dealing with recordings, live broadcast, or transmission, understanding and utilizing companding can significantly enhance the quality of your audio.