Audio compression is a critical aspect of music production and audio engineering. It helps to control the dynamic range of audio recordings and balance the levels of different sounds.
A compressor is a versatile tool used for a wide range of applications, but it is also one of the most misunderstood pieces of equipment in the audio world.
One of the essential parameters of a compressor is the compression ratio. In this article, we will discuss what an audio compressor ratio is, how it works, and its impact on audio recordings.
Let's get started.
What is a Compressor Ratio?
The compressor ratio is the amount by which the audio signal exceeds a set threshold, expressed as a ratio.
For example, if the ratio is set to 2:1, it means that for every 2 dB of audio signal above the threshold, the output will be 1 dB above the threshold.
In other words, the ratio determines how much the audio signal will be reduced in volume after passing the threshold.
The lower the ratio, the less the reduction in volume, and vice versa.
A low ratio (1.5:1 or 2:1) is used for light compression, which results in a subtle reduction in the dynamic range of an audio signal.
It is commonly used for controlling peaks, ensuring that no sound exceeds a certain level or causes distortion.
On the other hand, a high compression ratio (4:1 or more) is used for heavy compression, which results in a significant reduction in the dynamic range.
It is commonly used for controlling the overall volume level of an audio recording, reducing the difference between quiet and loud parts.
A low ratio setting will result in a natural and transparent sound, while a higher ratio will result in a more compressed and controlled sound.
The correct ratio depends on the type of audio recording and the desired effect.
For example, pop music and hip-hop often benefit from high compression ratios, while classical, jazz, and acoustic music often benefit from low compression ratios.
How to Calculate an Audio Compressor Ratio
Here is a simple method to calculate the compression ratio:
- Determine the threshold level: This is the level at which the audio compressor will begin to reduce the volume of the signal.
- Measure the input and output levels: measure the level of the audio signal before and after it passes through the compressor.
- Calculate the ratio: Divide the difference between the input level and the threshold level by the difference between the output level and the threshold level. This will give you the compression ratio.
For example, if the threshold level is set at -10 dB, and the input level is -6 dB, and the output level is -8 dB, the calculation would be (-6 dB - (-10 dB)) / (-8 dB - (-10 dB)) = 4:1.
In this example, the ratio would be 4:1, meaning that for every 4 dB that the input signal exceeds the threshold level, the output will be 1 dB above the threshold.
Calculating the ratio is a simple process that requires you to determine the threshold level, measure the input and output levels, and divide the difference between the input level and the threshold level by the difference between the output level and the threshold level.
What Exactly is 6:1 Compression?
In a 6:1 compression ratio setting, for every 6 dB that the input signal exceeds the set threshold level, the output will be only 1 dB above the threshold.
This means that the output signal will be reduced by a factor of 6 compared to the input signal, creating a significant reduction in the dynamic range of the audio.
6:1 compression is similar to 4:1 compression in that it is used for heavy compression and is often used to control the overall volume level of an audio recording, reducing the difference between quiet and loud parts.
This can be useful in musical genres such as pop and hip-hop, where a more compressed and controlled sound is desired.
However, it is important to be mindful of the amount of compression used, as excessive compression can result in a loss of musicality, character, and energy in the audio.
In general, the ratio should be adjusted based on the specific requirements of the audio recording and the desired sound.
It is important to experiment with different ratio settings to get the best results.
Here’s how certain ratio settings affect a signal:
1:1 - No matter how high the threshold level is, both input and output levels remain the same. As a result, no compression will be applied.
1.5:1 - Preserves the natural sound's peaks and valleys with a gentle, transparent compression.
2:1 - It allows the dynamics to be controlled smoothly without affecting the tone or punch of the track.
3:1 - With this ratio setting, compression is moderate but more aggressively controlled. A good amount of control is applied while maintaining natural dynamics.
4:1 - The signal is compressed at a medium ratio, which allows for better control. Punch, loudness, and tone will differ slightly.
10:1 - In addition to reducing dynamic range, it also reduces the punch, clarity, and presence of a signal.
20:1 to Infinity:1 - When you start applying this amount of ratio, the compressor effectively prevents the signal from crossing the threshold.
Understanding how the compression ratio works and its impact on audio recordings will allow you to make informed decisions when adjusting the compressor in your audio productions.
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