Understanding and Utilizing Audio Compressors 1: What is a Compressor?

An audio compressor plays a vital role in audio engineering and music production, serving as a “semi-automatic volume controller.” The primary purpose of a compressor is to narrow the dynamic range of the input signal. Dynamic range refers to the difference between the maximum and minimum levels of an audio signal.

compressor

Compressors are relatively simple yet can be tricky to utilize effectively. When properly used, they not only add consistency to volume but also allow for precise control over transients, sustain, and release of the envelope, playing a crucial role in mixing and arrangement. However, understanding the structure of the compressor and gaining practical experience is crucial. In this post, we will briefly explore the basic principles and parameters of a compressor.

Structure of a Compressor

Compressor


1. Input and Output

  • Input: Receives the audio signal that needs compression.
  • Output: Sends out the processed audio signal.

2. Threshold

Threshold
  • Compression starts only when the input signal level exceeds this value.

3. Ratio

Ratio
  • Sets the compression ratio applied to the portion exceeding the threshold. For instance, with a 4:1 ratio, every 4dB above the threshold results in a 1dB increase.

4. Attack and Release

Attack-and-Release
  • Attack: Determines how quickly the compression begins once the signal exceeds the threshold.
  • Release: Determines the speed at which compression is released when the signal level falls below the threshold.

Knee

Knee
  • Users can choose between Hard Knee and Soft Knee. Hard Knee applies compression instantly when the signal exceeds the threshold, whereas Soft Knee applies compression gradually.

Make-up Gain

  • Increases the signal level reduced by compression.

Detector Type

  • RMS detectors generally provide smoother and more natural compression, while Peak detectors enable fast and accurate level control. For transient control purposes, a Peak detector might be more suitable.

Side Chain

Sidechain
  • External Sidechain: Allows the compressor to operate based on the signal from another audio track. For example, the signal from a kick drum can control the compression of the bassline, reducing its volume each time the kick drum plays.
  • Internal Sidechain: Operates within the same audio track where the compressor is applied. For example, if you want the track to mainly respond to the high-frequency range, you can apply a high-pass filter to the compressor via the internal sidechain option.

Though audio compressors can be complex, their complexity offers tremendous flexibility and diverse applications. Understanding the basic principles and parameters enables effective audio processing. Each parameter interacts with others, and altering one can significantly impact the overall sound. Additionally, the appropriate use of a compressor varies depending on music genre, recording condition, and mixing goals, and the “correct” setting can vastly differ depending on the situation.