What is a limiter?

 

A Limiter, as its name suggest, is a audio effect that allows signals below a specified input power or level to pass unaffected while attenuating the peaks of the stronger audio signal that exceed this threshold. Modern versions often offer more than one limiter mode. However, we will state two main ones which are Limiting or dynamic range compression, and Clipping (audio) which is an extreme version of limiting.

 

The history of limiters

 

Back in the year 1935 Al Twone based in San Francisco developed an audio processor called PROGAR ( Program Guardian ). This audio processing tool can be described as a first audio limiter. It was a combined piece of audio equipment, consisted of an intelligent compressor ( with automatic gain control ) and a peak limiter. It took more than 10 years to Al Twone to patent its invention and sell it to Langevin. After that his audio processing tool became commercially available on the market.

The technology of the peak limiters significantly advanced in the early 1950`s. Back then, General Electric company introduced their BA-6 peak limiter and later BA-7 as its successor. The reason why those devices were so advanced was because they used input audio to modulate RF carrier and then all peak limiting was applied to the carrier. After demodulation, the audio was fed to the transmitter. It made huge success since this approach eliminated many unwanted audio artifacts. On the other hand, like the majority of the audio equipment of that time, two people are needed to lift and mount such a device into a rack.

 

Brickwall limiter

 

In modern times one of the highly used types of audio limiters are Brickwall limiters. They are mainly based in the digital domain. The brickwall is set in a way that nothing can pass the set of the threshold. Aside from its common use in modern music production, it also has its benefits in the “Live” situations. For example, live sound engineers often strap a brick wall limiter over their mixes to protect from sharp unexpected spikes, like a dropped microphone.

Radio broadcasts also use brick wall limiters for the same reason. Additionally, to ensure the sound never gets louder past a certain threshold. There are strict laws that radio broadcasts can’t be louder over a certain point, and likely there are steep fines. Hence the absolute necessity of a brick wall limiter. Typically, a digital “brick wall” limiter has a ratio of infinity: 1, and will use a look-ahead delay to analyze & process peak transients with extremely fast attack and release, relative to that of a compressor.

 

Catching the peaks

 

The limiter should be there in a digital system to catch the peaks because we have a digital maximum. The perceived loudness of a track doesn’t come from the direct reduction to the peak transient with a digital limiter. This will only ”dull” the sound. It comes from good frequency balance and use of effective compression. This is done to even the RMS level of the audio and the effective use of downwards compression/classic limiting. The digital limiter is then used to even out the peak material if necessary, depending on the genre as previously stated.

 

Additional Resources & Source Texts

 

http://www.thebdr.net/articles/audio/proc/proc-hist2.pdf