Limiters: Your Bodyguard


Manley VariMu Tube Limiter Compressor

A limiter, similar to a compressor, is a dynamic processor that controls the volume, or dynamic range, by limiting any peaks of the signal to an established threshold. The difference between a compressor and a limiter is that a compressor reduces the signal that passes the threshold by a lower set ratio, allowing for some of the sound to cross; a limiter does not. Limiters start at such a high ratio setting that the peaks of the signal are completely restricted to the threshold; nothing sonically excels above the given point.

Limiting processors in the audio industry are essentially bodyguards. Their main function in any situation is to provide insurance for your recordings by applying an unnoticeable amount of resistance to the amplitude of the tracked recording before reaching your choice of medium for storage. This prevents audio recordings from being overdriven, clipped, or even distorted.

For studio applications, limiters are hardly touched or even looked at. Gain-staging is a crucial factor in the studio environment, not to mention, everything that happens during recording is expected and gained to a certain level for storing and playback.  Thus, limiters are mostly seen in a combo version with other dynamic processors such as noise/gates, compressors, or both. In a combination package, depending on the manufacturer, limiters can be engaged on the unit by a switch specifying the use of the specific dynamic processor, or by using specified settings to engage the limiter; also known as peak limiting. An actual peak limiter will have two available threshold settings, one marked for the compressor when it normally acts as a compressor and one marked for the limiter to respond to once it reaches a certain level of dB’s above the first threshold. This lets the combination unit act as a compressor until it becomes overwhelmed in which the limiter takes over and completely limits the signal to a given set decibel level.

Crane Song STC-8 Discrete Class A Compressor/ Peak Limiter

Possible ratio settings for limiters start at 8:1 and include, 10:1, 20:1, 40:1, 80:1, and even 100:1. This means for every 100 dB’s passing through the threshold, only one dB of loudness makes it to the output. Dramatic ratio settings like these are commonly used for radio broadcasting to conserve bandwidth usage.

Limiters are commonly used for protection in these applications( Just a few):

  • Limiters are placed in the output chain to large cabinets(speakers) in live venues to protect the possibility of over driving and blowing the cabinets.
  • Limiters are used to limit the output of radio broadcasting to conserve bandwidth among the different stations.
  • Limiters are used in some mastering to protect from overdriving the master track for final output.
  • Limiters can be used as a peak limiting affect for Production Sound Mixers to protect the dialogue from unavoidable shouting or yelling that would clip or distort the recording.

Parameter Description:

Threshold: This is a set decibel level  in which limiting begins and ends. For example, if the threshold is set to -10dB, any audio signal that reaches a loudness of -10dB or above receives the specified ratio attenuation at that point; which usually leads to the output loudness only being -10db.

Ratio: The amount of attenuation the signal receives once it crosses the threshold. This reduces the sound by a division of what the signal could normally amplify to. In the instance of a limiter which starts off with a ratio of 8:1, the signal is only getting fractions of a decibel louder to the output which creates the effect of hearing the sound’s amplitude restricted.

Attack: Commonly you will see attack on combo units and plugins. This is generally a compression parameter and a setting is placed based on time or speed of action. For your limiter to work correctly, I would personally leave this in the fastest attack time possible to avoid any confusion with the timing of your limiter. You generally want them to act quickly to protect your recordings so using the fastest setting will ensure protection at the right moment.

Release: Also another parameter used for compression, and as well with the attack setting, this is also set based on time. I would again use the fastest time for release because the minute you don’t need to limit the signal, you don’t want it in your way. So set this parameter to the fastest setting so it will quickly let down its guard the moment it doesn’t need to protect your medium from being overdriven.

Gain(Makeup Gain): This is the amount of gain(decibels) added to the output of the limiter to compensate for the gain reduction from the limiter. This is normally used to bring the level of the signal back up to its respectable hearing that you thought would be adequate for the recording before you had to limit the signal.

Slope: Common with combo units and generally used for compressors, this parameter affects the exact moment at which the compressor begins reduction. This parameter can be set between either low and high or soft knee and hard knee. Both terms mean exactly the same thing, just that the equipment you may be using may use one term or the other, so watch out for it. If you are strictly limiting a signal then don’t bother with the slope, you want it to be hard or immediately engaged when called upon.

Hard Knee: The compressor/limiter reacts immediately when crossing the threshold. If limiting then make sure the limiter acting in this fashion.

Image of hard knee compression in action

Soft Knee: The compressor/limiter gradually starts when approaching the threshold. Avoid using if limiting. It can possibly be late for protecting that given moment if the circuitry allows for a soft knee to affect your limiter.

Image of soft knee compression in action

Side Chain (The Detector Circuit): Parameter used to control the compressor/limiter from an outside signal not passing through the limiter. Limiters are rarely used for this type of activity but you can still find uses for operations like this when the time presents itself.

Finally…

Limiters just like compressors, noise gates, or any other dynamic processors prefer the silent treatment. They love to be in on the action but enjoy being silent while at work. So, if you hear this component working on your audio then probably you are using them wrong. Limiters are like the odd cousin of the dynamic processing group, they are cool when you need them but eye soars mostly loafing around that you wish you didn’t have to see often.

For recording and mixing you may not use this tool as much, but don’t forget that it’s always there for insurance.

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