Compressor: Audio Filters

Audio filters are circuits of processed sound signals within an audio frequency range. There are several types of filters such as graphic equalizers, synthesizers and sound effects. These audio filters are designed to pass through frequency regions. Compressors are used to reduce the dynamic audio signals range. To sum it up, a compressor is an automatic volume control.

Tools and Materials Needed

  • Compressor

Step 1: Applying a Dynamic Range Compressor

This type of compressor, known as a DRC, is often used in car CD and DVD settings. The dynamic audio signal range is reduced which reduces the difference between low and high volumes. Apply this compressor by running the signal of an audio through dedicated hardware electronic units and/or through audio applications software. 

Step 2: Reduce the Dynamic Audio Signal Range

Downward compressions are used on loud sounds and reduced to a certain threshold, whereas quiet sounds are not treated. Upward compression makes sounds that are below threshold louder, and louder thresholds remain unchanged. These two types of compression minimize the dynamic audio signal range. This is often done for reasons of aesthetic because the human ear is unable to take in a dynamic range.

Step 3: Improve Audibility in a Noisy Environment

Using a compressor can improve sound in a noisy environment when background noise overpowers quiet sounds. This makes listening uncomfortable because the loud sounds make the quiet sounds inaudible. If you use compression to reduce the loud sounds level and not sounds that are quiet, then quiet sounds can be tuned to an audible level without the loud sounds that will be too loud. 

Step 4: Reducing Audio Signals Using Threshold Ratios

Compressors reduce the audio signal level when it is amplified over a specific threshold. To determine the ratio of the gained reduction amount, you will use a 4:1 ratio. This means if input levels are over a 4 dB threshold, then output signal will be 1 db over threshold. This reduces the level of gain by 3 dB. So, in short, the ratio determines input/output signals above threshold.

Step 5: Controlling How Quickly the Compressor Works

Compressors release and attack gain over a short period of time. This time is often measured in milliseconds. The so called attack phase is when the compressor is decreasing the gain to a level determined by the ratio. The release phase is when the compressor is increasing gain to a level determined by the ratio. You can adjust these attack and release phases by adjusting the input signal on the device the compressor resides on. As you can see, using audio filter compressors can make a big difference in the sounds you hear. Radio's, DVD's, CD players and many other devices use audio filter compressors to allow the human ear to have an enjoyable listening experience.

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