Compressors are an essential tool in recording and mixing studios, used to control the dynamic range of audio signals. They reduce the volume of loud sounds and increase the volume of soft sounds, resulting in a more consistent and balanced mix. The history and development of compressors have been crucial in the evolution of music production and have seen significant advancements in technology and design over the years.


What Different Kinds of Audio Compressors Are There?

There are many types of audio compressors, all offering different sonic flavours, characteristics and applications. Some of the common types are: Opto, Tube/Vari Mu, FET, VCA and Digital. In this article we will learn a bit about the history behind a few of these.


Audio Compressors Through Time

Compression can be traced back to the mid 1920s – 1930s, the early compressors were very basic with limited functions. Throughout the years the compressor technology has developed tremendously and in modern day recording it is almost treated as an instrument in itself.


Optical Compressors

The earliest compressors were optical compressors, which used a light-dependent resistor (LDR) to control the gain reduction. The LA-2A from Teletronix, introduced in the early 1960s, was one of the first commercially successful optical compressors. It was designed to compress vocals and acoustic instruments and became a staple in many studios due to its warm, natural sound. This type is often used for levelling and adding subtle dynamics control.


Tube/Vari-Mu Compressor

The tube compressor, also known as the vacuum tube compressor, was invented in the 1940ies. It emerged as a significant advancement in audio technology during the post-World War II era. One of the pioneering tube compressors was the Fairchild 660, introduced in 1959. The Fairchild 660 and its successor, the Fairchild 670, are regarded as iconic and highly sought-after tube compressors, known for their warm, rich and smooth characteristics.


FET Compressors

In the late 1960s early 1970s, FET (Field-Effect Transistor) compressors with Solid-State technology were introduced, offering faster attack times and greater control over the sound. It was developed as an alternative to vacuum tube compressors and was designed to provide a similar warm and musical characteristic. The 1176 from Universal Audio was one of the first solid-state compressors and quickly became popular due to its fast attack time and versatility. It was used on many iconic recordings, including those of The Beatles, Led Zeppelin, and The Rolling Stones. The FET compressor design has become a staple in the audio industry and has been replicated and modified by various manufacturers over the years.


VCA Compressors

In the 1970s, dbx introduced the VCA (voltage-controlled amplifier) compressor, which used an electronic circuit to control the gain reduction. The dbx 160 was one of the first VCA compressors and offered a transparent, uncoloured sound. It became popular for use on drums and other percussive instruments. VCA compressors are versatile and offer fast response times and precise control over the compression parameters.


Digital Compressors

In the 1980s, digital signal processing (DSP) technology was introduced, which allowed for more precise control over the audio signal. These compressors are software-based or hardware devices that utilise DSP techniques to achieve compression. The first digital compressor, the dbx 905, was introduced in 1984 and used a 20-bit DSP chip for gain reduction. Other digital compressors soon followed, including the TC Electronic Finalizer, which offered a range of advanced processing options and became popular for mastering.
Digital compressors offer a wide range of features and can emulate the characteristics of various analogue compressors or provide unique digital algorithms.


Modern Day Audio Compressors

Today, there are numerous types of compressors available, including analogue, digital, and software-based compressors. Manufacturers such as SSL, Empirical Labs, and Waves continue to innovate and push the boundaries of compressor design, offering new features and capabilities to meet the evolving needs of music production.


What is Multi-Band Compression?

One notable recent development is the use of multi-band compression, which allows for different frequency bands to be compressed independently. This can result in a more transparent and natural sound, as well as greater control over the mix.


What is Side-Chain Compression?

Another recent development is the use of sidechain compression, which allows for specific frequencies or instruments to trigger the compressor. This can be used to create a “pumping” effect on dance music, or to reduce the volume of a specific instrument in a mix.

In conclusion, compressors have been an essential tool in recording and mixing studios for many decades, offering greater control over the dynamic range of audio signals. The development of different types of compressors, including optical, solid-state, VCA, and digital compressors, has resulted in a wide range of options for music producers and engineers. The continued innovation and advancement of compressor technology and design are sure to play a significant role in the future of music production.


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