In audio engineering, both limiters and compressors are dynamic processors used to control the volume level of audio signals. However, they have different functions and applications, and understanding their differences is crucial to using them effectively.
What Does a Compressor Do?
A compressor is used to reduce the dynamic range of an audio signal by automatically reducing the gain (volume) of the audio signal when it exceeds a certain threshold. This means that the quieter parts of the audio signal are boosted, while the louder parts are reduced, resulting in a more even and consistent volume level.
Compressors are often used in music production to add sustain to guitar and bass sounds, smooth out vocal performances and tighten up drum tracks.
What Does a Limiter Do?
On the other hand, a limiter is a type of compressor that is designed to prevent audio signals from exceeding a certain level, called the “limiting threshold.” When the signal exceeds this threshold, the limiter automatically reduces the gain of the audio signal to prevent it from distorting or clipping. In other words, limiters are used to prevent audio signals from getting too loud and causing distortion, which can be particularly important in live sound-ups and broadcast applications.
Ratio Control
One key difference between compressors and limiters is their ratio setting. A compressor typically has a variable ratio control that determines how much the gain reduction is applied to the audio signal when it exceeds the threshold. This ratio can range from 1:1 (no compression) to infinity:1 (hard limiting). In contrast, a limiter typically has a fixed ratio of 10:1 or higher, which means that any audio signal that exceeds the threshold will be reduced to a level that is 10 times lower than the original signal.
Attack & Release
Another difference between compressors and limiters is their attack and release settings. The attack time of a compressor determines how quickly the gain reduction is applied to the audio signal when it exceeds the threshold.
A fast attack time is often used to control transient peaks in the audio signal, while a slower attack time is used to let the initial transient through before the gain reduction is applied. In contrast, the attack time of a limiter is typically set to its fastest setting to quickly respond to any signal that exceeds the threshold.
The release time of a compressor determines how quickly the gain reduction is removed when the audio signal falls below the threshold. A fast release time can result in pumping and breathing artifacts, while a slow release time can result in a loss of perceived loudness. In contrast, the release time of a limiter is typically set to a fixed value that is faster than that of a compressor, to prevent any overshoots above the threshold.
Using a Compressor In Mastering
The compression used in mastering is a different approach to that used on individual tracks in the mixing process, and must be used carefully and in moderation.
Applying too much compression can result in a loss of dynamic range and musicality, and can make a mix sound flat and lifeless. As such, it is important to approach compression with a light touch and use it as a tool to enhance the natural dynamics and musicality of a mix, rather than as a crutch to fix problems that could be better addressed at an earlier stage in the mix.
The compression technique used in mastering is known as glue compression. This is also used in mixing at the Bus (aux) level of the mixing desk. It is used in to help create a more cohesive and unified sound across a mix. The idea behind glue compression is to use a compressor to gently compress the mix as a whole, rather than just individual tracks or instruments.
By using a compressor with a slow attack time and a relatively fast release time, the transient peaks are gently reduced, and the overall level of the mix is increased. This helps to bring out the subtle details in the mix and creates a more polished, professional sound.
One of the benefits of glue compression is that it can help to create a more cohesive sound, even when the individual tracks or instruments have different dynamic ranges or tonal characteristics. By gently compressing the mix as a whole, the engineer can bring out the subtle nuances and textures that might otherwise get lost in the mix.
Glue compression should be used judiciously and with care, as excessive compression can result in a loss of dynamics and musicality. The key to successful glue compression is to use a light touch and to carefully adjust the compressor settings to achieve the desired effect. By doing so, the engineer can create a more cohesive and polished sound that enhances the natural musicality of the mix.
Using a Limiter In Mastering
Limiters are an essential tool in the mastering process because they help to prevent clipping and distortion, which can occur when the signal levels exceed the maximum level that the digital audio format can handle.
When a signal exceeds the maximum level, it gets clipped, which can result in harsh, unpleasant-sounding distortion. This can be particularly problematic for music that is intended to be played on a variety of different playback systems, as different systems may have different maximum levels.
A limiter in mastering is used to control the peak levels of a mix so that they do not exceed a certain threshold. This threshold is typically set just below the maximum level of the digital audio format, such as 0.10 dBFS (decibels relative to full scale). By controlling the peak levels of the mix, the limiter helps to prevent clipping and distortion, while still allowing the overall level of the mix to be increased to a competitive level.
Another reason why a limiter is used in mastering is to create a more consistent and balanced sound across the entire mix. By reducing the dynamic range of the mix and increasing the perceived loudness, a limiter can help to create a more cohesive sound that translates well on different playback systems. This is particularly important in today’s music industry, where music is often consumed in a variety of different environments, such as headphones, car stereos, portable speakers and phone and tablet devices.
It’s worth noting that using a limiter in mastering requires careful consideration and attention to detail, as excessive limiting can result in undesirable artifacts, such as pumping and glitches/ digital pops (on digital limiters). Additionally, applying too much limiting can result in a loss of dynamic range, which can negatively impact the overall sound quality and musicality of the mix.
As such, a skilled mastering engineer will use a combination of careful level matching, equalization and other processing techniques to achieve the desired result, while still preserving the integrity and musicality of the original mix.
In Summary
While both limiters and compressors are used to control the volume level of audio signals, they have different functions and applications.
Compressors are used to reduce the dynamic range of audio signals, while limiters are used to prevent audio signals from exceeding a certain level to prevent distortion. Understanding the differences between the two can help you make informed decisions about which tool to use in different situations to achieve the desired effect.
About the Author: Hey, I’m Peter, I run AM Mastering. I create balanced, dynamic masters for many different genres of music. Need your music mastered? Get in touch today.