The History of Compressor/Limiters
October 18, 2023
Compressor/limiters are devices that reduce the dynamic range of an audio signal, which is the difference between the loudest and quietest parts of the sound. Dynamic range compression can make the audio sound louder, more consistent, and punchier, as well as prevent distortion and clipping. The origins of compressor/limiters can be traced back to the broadcast industry, where they were used to prevent over-modulation of radio signals. Over-modulation occurs when the audio signal exceeds a certain level and causes the radio wave to distort and lose information. Compressor/limiters were designed to automatically lower the volume of loud sounds above a threshold, while leaving the quiet sounds unaffected. This way, the audio signal could be transmitted without distortion and with a higher average level.
The birth of the audio compressor
Early Compressor/Limiters
Audio compressors, a staple in modern recording studios for taming vocal peaks and adding punch to drums, actually have roots outside the recording world. Originally, compressors were designed for telephone lines and then radio broadcasting to manage audio peaks in radio transmitters. In the early days of radio, level spikes could lead to overmodulation, causing distortion and interference that disrupted broadcasts and neighbouring channels.
To prevent this, engineers developed compression technology that kept signal levels consistent, ensuring clear and reliable transmission. Over time, music producers discovered the artistic potential of compressors, realising they could use the same tools to add warmth, control dynamics, and shape the energy of a mix. What began as a technical solution for stable radio signals has since evolved into an essential creative tool, forever changing the way we experience recorded music.
The earliest example of a compressor/limiter was the Western Electric 110A, which was developed in 1931 for telephone lines. It used a variable resistor controlled by an electro-mechanical device that measured the signal level. The Western Electric 110A was later adapted for radio broadcasting and recording studios.
The Western Electric 110A Program Amplifier, released in 1937, was a pioneering broadcast audio compressor designed to enhance radio transmission quality and prevent over-modulation. Known as the first compressor of its kind, this amplifier delivered a 3 dB increase in average audio signal level, effectively doubling the broadcast area without needing additional transmitter power.
The Western Electric 110A Program Amplifier also allowed operators visual confirmation of levels through an indicator lamp that flashed when peaks surpassed a set threshold. Its durable construction was ideal for rack mounting, featuring intuitive front-panel controls and a self-contained power supply for easy integration. With a transmission range of 30 to 10,000 Hz and less than 1% distortion, the Western Electric 110A was an engineering milestone in early broadcast compression technology.
In the early 1940s, the world of audio processing saw a major leap forward with new, advanced methods for peak limiting.
When General Electric launched the BA-5 delay-line peak limiter in 1947, it transformed the broadcasting landscape. This device used a feed-forward technique with a delay line, allowing the audio signal to synchronise with the bias generator – a truly innovative feature for its time. In fact, it would be many years before any other equipment could replicate its standout capabilities.
The result? The BA-5 delivered audio clarity that was unprecedented. But just how impressive was this limiter? NBC, despite a strict policy of using only RCA equipment, couldn’t resist the BA-5. They even repainted these units in RCA’s standard umber grey and added the RCA logo, turning them into “RCA Peak Limiters.” Thanks to this covert modification, every NBC station soon experienced a significant boost in audio quality.
Another early compressor/limiter was the RCA BA-6A, which was introduced in 1951. It used a variable-mu tube circuit that changed its gain depending on the input signal level. The RCA BA-6A had a fast attack time and a smooth release time, making it suitable for voice and music applications. It was widely used by radio stations and record labels such as Capitol Records and Motown.
Western Electric 110A Program Amplifier, designed to protect radio towers in the radio broadcast industry.
The groundbreaking General Electric BA-5 Limiting Amplifier from 1947.
In the 1950s and 1960s, compressor/limiters became more sophisticated and versatile, with features such as variable attack and release times, ratio, threshold, and makeup gain. Some of the most famous models from this era include the Gates STA-Level, a variable MU compressor which itself has spawned many replicas and influenced the design of many compressors.
The Holy Grail of Vintage Compressors
Fairchild 670 Tube Limiter
The Fairchild 660 and Fairchild 670, were introduced in 1959 and 1960 respectively. They were tube-based compressor/limiters that used a photoresistor and a light source to control the gain reduction. Designed for mastering duties in the cutting room, these compressors eventually found their way to the studio due to their very smooth and musical sound. They were favoured by engineers such as George Martin, Phil Ramone, and Geoff Emerick.
They were used on many classic recordings by artists such as The Beatles, Frank Sinatra, Ray Charles, and Pink Floyd. Today, they are the most sought-after compressor from this early period, however they rarely come up for sale and when they do, the price is incredibly high. There are of course many replicas of these classic compressors, but even they are rather costly.
Second only to the 1176
Teletronix LA-2A Levelling Amplifier
The Teletronix LA-2A, released in 1962, is one of the most revered compressors in recording history. Its optical compression design uses a light-dependent resistor and luminescent panel to control gain reduction, delivering a smooth, natural compression with a unique character. The all-tube circuitry, featuring components like the 12AX7 and EL84 tubes, adds warmth and harmonics, making the LA-2A particularly musical.
With only two controls – Peak Reduction to set compression amount and Gain for output level – the LA-2A is both powerful and easy to use. Its fixed compression ratio, typically around 4:1 but responsive to input level, provides a soft-knee compression curve that preserves the natural dynamics of vocals, bass, and other dynamic sources.
After Universal Audio acquired Teletronix, the LA-2A became a signature product for Bill Putnam’s company. It has since seen numerous reissues and emulations, maintaining its place as an essential studio tool. Its warm, transparent sound and ability to gently shape audio without harshness have made it a favourite for engineers worldwide, especially on vocals and expressive instruments. The LA-2A remains a benchmark for smooth, classic compression.
The LA-3A released several years after the LA-2A, was essentially a transistorised version of the LA-2A, which has never managed to replace the legendary compressor on which it is based.
“Like the 1176, it would be nearly impossible to find a professional recording studio that does not have at an LA-2A compressor in their racks”
The Teletronix LA-2A was used on these classic recordings
A true studio legend
Urei 1176 Limiting Amplifier
The Universal Audio 175, 175B, and 176 compressors, released in the early 1960s, were some of the first tube-based compressors and are known for their warm, smooth compression. The 175B improved on the original 175 with lower noise, while the 176, released in 1963, added variable ratios and attack/release controls for more flexibility. These tube designs set the foundation for the iconic 1176, which Universal Audio introduced in 1967 as a solid-state alternative, offering faster, punchier compression with a different sound profile. The 175 and 176 remain highly valued for their rich, classic tonal quality.
The Urei 1176 was a solid-state compressor/limiter that used a field-effect transistor (FET) to control the gain reduction. It had a very fast attack time and a distinctive sound that added punch and presence to the audio. It was widely used on vocals, drums, guitars, and bass. It was used by engineers such as Bruce Swedien, Eddie Kramer, and Bob Clearmountain. It was used on many hit records by artists such as Led Zeppelin, Michael Jackson, Stevie Wonder, and AC/DC.
Note: Universal Audio, Teletronix, and UREI were all companies owned by Bill Putnam, and many of their products displayed multiple brand names. For example, the 1176 compressor had Universal Audio on the front and UREI on the back, leading to considerable confusion over branding.
“It would be near on impossible to find a professional recording studio that does not have at least one 1176 compressor in their racks”
The UREI 1176 was used on these classic recordings
A couple of rare compressors
Altec 1612A Compressor Limiter
In 1967, Altec (Lansing) introduced the Altec 1591A, designed for effortless mixing of high- and low-level inputs, offering compression or linear amplification while preserving dynamic range. It was ideal for recording and broadcast studios, theatres, stadiums, schools, churches, hotels, arenas, convention centres, military complexes, and public address systems.
Following the 1591A’s success, Altec released the Altec 1612A Compressor Limiter, a unit that, like its predecessor, remains highly sought after today but is rarely available for sale. The 1612A’s production run was likely cut short by the arrival of the dbx 160, which gained significant popularity just a year after the 1612A’s release.
The Altec 1591A Compressor Limiter
The sound of the 1970s
dbx 160 Compressor/Limiter
The dbx 160 (released in 1976) is a single-channel compressor/limiter combining sophisticated technology and user-oriented features in a compact package. Unique circuit designs, such as true rms level-detection and feed-forward gain reduction, place the dbx 160 in a completely different class from conventional compressor/limiters that came before it.
The dbx 160 was a solid-state compressor limiter that used a voltage-controlled amplifier (VCA) to control the gain reduction. The dbx 160 had a very hard-knee characteristic and a linear detection circuit that made it very effective at controlling transients and peaks. It was widely used on drums, bass, guitars, keyboards, and vocals. The dbx 160 was used by engineers such as Bob Ludwig, Bob Clearmountain, and Roger Nichols. It was used on many hit records by artists such as The Police, Madonna, Prince, and Dire Straits.
“The DBX 160 VU Compressor/Limiter is a classic for a reason. It’s been a stalwart in my studio for decades. The compression and limiting it offers is excellent. This workhorse can handle anything you throw at it, from drums to vocals, with finesse. If you’re after a reliable and timeless piece of gear, this is it. A true legend in the world of audio processing.”
The DBX 160 was used on these classic recordings
Legendary British Compressor
SSL G Series Bus Compressor
The SSL G Series Bus Compressor, which was introduced in 1981. It was a solid-state compressor/limiter that used a VCA to control the gain reduction. It had a soft-knee characteristic and a non-linear detection circuit that made it very effective at gluing together the mix bus. It had a signature sound that added punch and cohesion to the audio. It was widely used on the master bus of the SSL G Series consoles, which were popular in the 1980s and 1990s. It was used by engineers such as Chris Lord-Alge, Andy Wallace, and Spike Stent. It was used on many hit records by artists such as Queen, U2, Michael Jackson, and Nirvana.
In the 1990s and 2000s, compressor/limiters became more software-based and accessible, with features such as digital signal processing, graphical user interfaces, presets, automation, and plug-in formats. Many of the plugins available emulate these classic hardware compressor/limiters, with some emulations being better than others. Compressor/limiters are still evolving and innovating today, with new models and features being developed and released every year. They are one of the most essential and ubiquitous tools in audio production, with applications ranging from recording to mixing to mastering to live sound. They have shaped the sound of music and audio for decades and will continue to do so for years to come.
