Compressor vs. Limiter

Attribute	Compressor	Limiter
Function	Reduces the dynamic range of audio signals by attenuating the volume of loud sounds	Prevents audio signals from exceeding a certain threshold by instantly reducing the volume
Threshold	Can be adjusted to determine the level at which compression starts to occur	Has a fixed threshold level above which no audio passes through
Ratio	Controls the amount of gain reduction applied to the audio signal above the threshold	Does not have a ratio control, as it applies a fixed amount of gain reduction
Attack Time	Determines how quickly the compressor responds to audio signals above the threshold	Usually has an extremely fast attack time to instantly reduce audio levels
Release Time	Determines how long it takes for the compressor to stop attenuating the audio after it falls below the threshold	Usually has a fast release time to quickly return to normal audio levels
Gain Makeup	Allows for compensating the overall gain reduction applied by the compressor	Does not typically have a gain makeup control, as it applies a fixed amount of gain reduction
Applications	Used in music production, broadcasting, and sound engineering to control dynamics and add character to audio	Commonly used in live sound reinforcement and mastering to prevent audio distortion and protect equipment

Introduction

When it comes to audio processing, two commonly used tools are compressors and limiters. Both serve the purpose of controlling the dynamic range of audio signals, but they have distinct characteristics and applications. In this article, we will explore the attributes of compressors and limiters, highlighting their similarities and differences.

Compressor

A compressor is an audio processing device that reduces the dynamic range of an audio signal. It achieves this by attenuating the level of the audio signal above a certain threshold. Compressors are widely used in music production, broadcasting, and live sound reinforcement to control the volume fluctuations and ensure a more consistent audio output.

One of the key attributes of a compressor is its adjustable ratio. The ratio determines the amount of gain reduction applied to the audio signal above the threshold. For example, a 4:1 ratio means that for every 4 dB the input signal exceeds the threshold, the output will only increase by 1 dB. This allows for precise control over the dynamic range.

Another important attribute of a compressor is the attack time. The attack time determines how quickly the compressor responds to a signal that exceeds the threshold. A fast attack time can help tame transient peaks, while a slower attack time preserves the natural dynamics of the audio signal. Adjusting the attack time is crucial to achieving the desired compression effect.

Additionally, compressors offer a release time parameter. The release time determines how long it takes for the compressor to stop attenuating the audio signal once it falls below the threshold. A shorter release time can result in a more transparent compression, while a longer release time can create a more noticeable pumping effect.

Compressors also provide a makeup gain control, which allows the user to compensate for the overall level reduction caused by compression. This ensures that the output level matches the desired loudness, even after applying compression.

Limiter

A limiter, like a compressor, is an audio processing tool used to control the dynamic range of audio signals. However, a limiter is designed to provide a more extreme form of compression, preventing the audio signal from exceeding a certain level, often referred to as the "ceiling."

The primary attribute of a limiter is its high ratio, typically ranging from 10:1 to infinity:1. This means that any signal exceeding the threshold will be significantly attenuated, effectively "limiting" its maximum level. Limiters are commonly used in mastering, broadcasting, and live sound applications where preventing signal clipping and ensuring a consistent output level is crucial.

Unlike compressors, limiters have a very fast attack time, often measured in microseconds. This allows them to instantaneously respond to any signal that exceeds the threshold, preventing any overshoots or transients from passing through. The fast attack time of a limiter makes it an effective tool for controlling peaks and protecting audio equipment from potential damage.

Similarly to compressors, limiters also offer a release time parameter. However, the release time of a limiter is typically shorter than that of a compressor. This ensures that the limiter quickly stops attenuating the audio signal once it falls below the threshold, allowing for a more transparent operation.

Another attribute of limiters is the ability to set the ceiling level. The ceiling determines the maximum level to which the audio signal can be limited. By setting the ceiling slightly below 0 dBFS (the maximum digital level), limiters prevent any signal from exceeding the digital clipping point, ensuring a distortion-free output.

Similarities

While compressors and limiters have distinct attributes, they also share several similarities. Both tools are used to control the dynamic range of audio signals, ensuring a more consistent output. They both have threshold controls to determine the level at which the processing begins. Additionally, both compressors and limiters provide makeup gain controls to compensate for the level reduction caused by their respective processing.

Furthermore, both compressors and limiters can be found in hardware form, as standalone units, or as software plugins. This allows for flexibility in their usage, whether in a studio environment or in live sound applications. The availability of compressors and limiters in various formats makes them accessible to a wide range of audio professionals and enthusiasts.

Differences

While compressors and limiters share similarities, they also have distinct attributes that set them apart. Compressors are typically used for more subtle dynamic control, allowing for a more natural and transparent sound. On the other hand, limiters are designed for more aggressive and extreme compression, preventing any signal from exceeding a certain level.

Compressors offer adjustable ratios, attack times, and release times, allowing for precise control over the dynamic range. Limiters, on the other hand, have high fixed ratios and very fast attack times, ensuring instantaneous response to any signal that exceeds the threshold.

Another difference lies in their applications. Compressors are commonly used in music production to shape the dynamics of individual tracks or the overall mix. They are also used in broadcasting to control the volume fluctuations between different programs or commercials. On the other hand, limiters are often employed in mastering to achieve a consistent output level across an entire album or to prevent signal clipping in live sound reinforcement.

Lastly, the ceiling level is a unique attribute of limiters. By setting the ceiling slightly below 0 dBFS, limiters prevent any signal from exceeding the digital clipping point, ensuring distortion-free audio. Compressors do not have a specific ceiling level, as their purpose is to control the dynamic range rather than limit the maximum level.

Conclusion

Compressors and limiters are essential tools in audio processing, offering control over the dynamic range of audio signals. While they share similarities, such as threshold controls and makeup gain, they also have distinct attributes that make them suitable for different applications. Compressors provide more subtle and adjustable compression, while limiters offer extreme compression and prevent signal clipping. Understanding the attributes of compressors and limiters allows audio professionals to make informed decisions when it comes to shaping the dynamics of their audio signals.