What is the ratio in compression

Basic Elements: Ratio

Audio compression is based on several key parameters that determine how the compression process is applied to an audio signal. Understanding these elements is essential to using a compressor effectively. The following are the concepts of ratio, threshold, attack, release, and makeup gain.

Ratio (Compression Ratio)

The ratio defines the amount of gain reduction that will be applied to the signal that exceeds the threshold. It is expressed as a ratio, for example, 2:1, 4:1, or 10:1. This ratio indicates that for each specific number of decibels (dB) that the signal exceeds the threshold, only a fraction of those decibels will be allowed to pass.

• 2:1: For every 2 dB that the signal exceeds the threshold, only 1 dB will pass.
• 4:1: For every 4 dB that the signal exceeds the threshold, only 1 dB will pass.
• 10:1: For every 10 dB that the signal exceeds the threshold, only 1 dB will pass.

A higher ratio results in more aggressive compression, while a lower ratio allows for more subtle compression.

How the ratio works

Ratio is expressed in a numerical ratio, such as 2:1, 4:1, 10:1, etc. The first number represents the amount of input needed to increase 1 unit in output.

Become an expert in compression with the recommended book “ Compression in Music Production” (click on the image to go to the link):

Practical example:

• If the ratio is 4:1, it means that for every 4 decibels (dB) that the signal exceeds the threshold, only 1 dB will go into the final output.
• If the signal exceeds the threshold by 8 dB:
  • With a ratio of 2:1, only 4 dB above the threshold will be heard.
  • At a ratio of 4:1, 2 dB above the threshold will be heard.
  • At a ratio of 10:1, you will hear just 0.8 dB above the threshold.

Common ratio settings and their uses

The ratio directly affects the intensity of the compression. Below are some common values and how they are typically used:

1. 1.5:1 to 2:1 (Light Compression):
   • Used for subtle control of dynamic range.
   • Ideal for vocals or instruments that need transparent compression.
2. 3:1 to 4:1 (Moderate compression):
   • Very common in vocal, guitar and drum mixes.
   • Provides effective control without sacrificing too much dynamic character.
3. 6:1 to 10:1 (Heavy Compression):
   • Used to tame very unbalanced signals or control extreme peaks.
   • Common on percussive instruments or tracks with a lot of dynamic variation.
4. 20:1 or more (Limiter):
   • In this range, the compressor acts as a limiter, preventing the signal from exceeding a specific level.
   • Used in masters to ensure that there is no clipping distortion.

How to set the ratio correctly

Choosing the right ratio depends on the type of audio and the desired effect:

1. Identify the problem: Does the signal have high peaks? Does it sound uneven? Does it need more presence?
2. Set the threshold first: Adjust the threshold so that the compressor acts only on the problematic parts.
3. Try different ratios: Start with a low ratio and progressively increase it until you find the balance between control and naturalness.
4. Watch the gain reduction meter: This will help you see how much compression is being applied.

Common mistakes when using the ratio

1. Using too high a ratio: This can cause the audio to sound “squashed” and lose its natural dynamics.
2. Not setting the threshold right: If the threshold is too high, the compressor will do nothing, and if it is too low, it will over-compress.
3. Ignoring context: The same ratio can work differently depending on the genre of music and the elements in the mix.

The ratio in a compressor is a fundamental parameter that defines how much compression will be applied to the signal. From light compression for subtlety to high ratios for total control, understanding and correctly adjusting this parameter is key to achieving balanced, professional mixes. Practice with different settings and listen closely to the results to master the art of compression.

Experiment and take your mix to the next level!