Audio Limiter

What Is a Limiter?

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

The History of Limiters

In 1935, Al Twone, based in San Francisco, developed an audio processor called PROGAR ( Program Guardian ). This audio processing tool was the first audio limiter. It was a combined audio equipment consisting of an intelligent compressor ( with automatic gain control ) and a peak limiter. It took over 10 years for Al Twone to patent and sell its invention 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 1950s. Back then, General Electric company introduced its BA-6 peak limiter and later BA-7 as its successor. Those devices were advanced because they used input audio to modulate the RF carrier, and then all peak limiting was applied to the carrier. After demodulation, the audio was fed to the transmitter. It was a huge success since this approach eliminated many unwanted audio artifacts. On the other hand, like most of the audio equipment of that time, two people had to lift and mount such a device into a rack.  

Brickwall Limiter

In modern times, the brick wall limiter is the most widely used type of audio limiter. They are mainly based in the digital domain. The brick wall is set so that nothing can pass the threshold set. Aside from its common use in modern music production, it also has its benefits in "Live" situations. For example, live sound engineers often strap a brick wall limiter over their mixes to protect them 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 say radio broadcasts can't be louder over a certain point, and there are likely steep fines. Hence, there is an absolute necessity for 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 a compressor.  

Catching the Peaks

The limiter should be 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 the use of effective compression. You can do this to even the RMS level of the audio and the effective use of downward compression/classic limiting. The digital limiter is then used to even out the peak material if necessary, depending on the genre, as previously stated.