What Is an Optical Compressor? (Answered)

You might be wondering what an optical compressor is and what it does. Find out the function of an optical compressor and how it can help you.

Are you looking to add some punch and clarity to your mix? Look no further than the optical compressor! With its smooth, transparent compression and range of adjustable controls, this dynamic range compressor is a go-to choice for recording and live sound engineers.

From taming explosive drums to adding sustain to vocals, an optical compressor is a versatile tool that can help bring your music to the next level. In this article, we will give you an overview of what an optical compressor is and explain how it can help you with your audio. So if you’re looking for a tool to reduce file sizes, this post is for you!

What is an optical compressor? An optical compressor is a type of analog compressor that utilizes a light element and optical cell to shape the dynamics of an audio signal. When the volume of the audio signal increases, the light element emits more light, which in turn causes the optical cell to reduce the amplitude of the output signal.

Image of an optical compressor and other audio equipments. Source: cottonbro studio, pexels
Image of an optical compressor and other audio equipments. Source: Cottonbro Studio, Pexels

What is an optical compressor?

An optical compressor is a type of audio compressor that uses an optical isolator circuit comprised of a light source such as a light bulb or LED and a photocell. The light source glows brighter or dimmer depending on the input level, while the photocell reads the varying brightness of the light source and changes gain accordingly. This process results in a slower and smoother response time compared to other types of compressors.

Optical compressors are known for imposing their own character on the material being treated, making it sound larger than life, especially when they do not use super-well-behaved integrated optical circuits or use them imaginatively. They are as much an effect as a gain-control device, making them popular among recording and mixing engineers who want to achieve a specific sound or tone for their recordings.

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How does an optical compressor work?

The optical attenuator, known as the T4B, is a key component of an optical compressor. This device contains two photocells, which are light-dependent resistors that alter their resistance value based on the amount of light they are exposed to.

The resulting change in resistance value causes the audio signal to be compressed, resulting in the distinctive sound of an optical compressor. The amount of gain reduction applied is determined by the ratio setting of the compressor, which specifies the amount of compression applied for every decibel the signal exceeds the threshold.

Optical compressors also have attack and release controls, which determine how quickly the compressor responds to the incoming audio signal and how quickly it releases the gain reduction once the signal falls below the threshold.

Optical compressors work by continuously monitoring the audio signal level and adjusting the gain accordingly to achieve the desired level of compression.

In addition, the make-up gain control allows the user to boost the overall level of the compressed signal to compensate for any loss of volume that may have occurred during the compression process.

Optical compressors work by continuously monitoring the audio signal level and adjusting the gain accordingly to achieve the desired level of compression. This process helps to even out the dynamic range of the audio and adds sustain, clarity, and punch to the sound.

Characteristics of optical compressors

Optical compressors are known for a few key characteristics, including:

  • Low distortion due to the use of a light-dependent resistor
  • Relatively slow attack and release times
  • Non-linear attack and release controls
  • Frequency-dependent attack
  • Transparent, natural sound
  • A soft knee allows for smooth transitions between compressed and uncompressed signal levels.

Where should you use an optical compressor?

Optical compressors are commonly used in recording and live sound settings to even out the dynamic range of an audio signal and add sustain, clarity, and punch to the sound. They are often used on vocals, drums, bass, and other instruments to achieve these effects.

In the recording studio, optical compressors can be used on individual tracks during the tracking or mixing stages or on the mix bus to add overall glue and punch to a mix. They are particularly useful for taming transient-heavy sources such as drums and percussion and can also add sustain and clarity to vocals and other instruments.

In live sound settings, optical compressors can be used on the front-of-house mix or on individual instruments in the monitor mix to help control the dynamic range and improve the overall clarity and punch of the sound. They are also commonly used on vocals to help the vocals cut through the mix and be heard clearly by the audience.

Optical compressors are versatile tools that can be used in various recording and live sound situations to shape the dynamics of an audio signal and improve the overall sound quality.

Image of an optical compressor with red and blue lights. Source: andreu marquès , pexels
Image of an optical compressor with red and blue lights. Source: Andreu Marquès , Pexels
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Benefits of using an optical compressor

There are several advantages to using an optical compressor:

1. Smooth, transparent sound

Optical compressors are known for their smooth, transparent compression that preserves the integrity of the original audio signal. This makes them a good choice for recording engineers who want to achieve a polished, professional sound without introducing unwanted distortion or coloration.

2. Versatility

Optical compressors are highly versatile and can be used on various instruments and vocals to achieve various effects. They are particularly useful for taming the sound of drums and percussion and can also let vocals and other instruments be heard more clearly.

3. Easy to use

Optical compressors often have a simple, straightforward design with a limited number of controls, making them easy to use even for those new to compression.

4. Durability

Optical compressors are generally very reliable and durable, making them a good choice for use in live sound settings where dependability is important.

5. Classic sound

Many classic compressors, such as the Urei 1176, are optical and have contributed to the sound of numerous hit records over the years. An optical compressor can help you achieve a classic, timeless sound in your recordings.

If you want even more tips and insights, watch this video called “What are Optical Compressors? | Too Afraid To Ask” from the CSGuitars YouTube channel.

A video called “What are Optical Compressors? | Too Afraid To Ask” from the CSGuitars YouTube channel.

Frequently asked questions (FAQ)

Do you still have questions about an optical compressor? Below are some of the most commonly asked questions.

What is the difference between optical and FET compressors?

Field Effect Transistor (FET) compressors are known for adding punch and character to a sound and can be particularly effective on percussive sounds or those with distinct transients. One well-known example of a FET compressor is the Urei 1176. On the other hand, optical compressors utilize a photocell and light bulb to control the gain reduction applied to the audio signal.

Is 1176 an optical compressor?

The Florence 1176 is an optical compressor that takes inspiration from the classic 1176 compressor but features a modern optocoupler. This allows it to offer three different modes of operation: compressor, limiter, and sustainer. It is an evolution of the original 1176 design.

Should vocals always be compressed?

Compression can be a useful tool for controlling the dynamics of vocals or other elements in a mix. The amount of compression applied will depend on the performance style and the music genre. In pop music, for example, vocals are often heavily compressed with a minimal dynamic variation.

Conclusion

So there you have it – a brief overview of what an optical compressor is and how it works. Whether you’re a seasoned audio engineer or just starting, an optical compressor is a valuable tool that can help you achieve the professional-quality sound in your recordings and live performances.

So, do you use an optical compressor? And did I cover everything you wanted to know? Let me know in the comments section below (I read and reply to every comment). If you found this article helpful, share it with a friend, and check out my full blog for more tips and tricks on music production. Thanks for reading, and never stop making music.

Key takeaways

This article covered what an optical compressor is. Here are some key takeaways:

  • An optical compressor is a gain-reduction circuit that relies on an optical photocell (a light source and a light detector). 
  • The optical attenuator, known as the T4B, is a key component of an optical compressor. This device contains two photocells, which are light-dependent resistors that alter their resistance value based on the amount of light they are exposed to. 
  • Optical compressors are known for a few key characteristics.
  • Optical compressors are commonly used in recording and live sound settings to even out the dynamic range of an audio signal and add sustain, clarity, and punch to the sound.

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Written by Andrew Ash, Staff Writer

Hey there! My name is Andrew, and I've been making music since I was a kid. I now run this blog all about home studios and music production. If you want to improve your home studio setup, this is the place for you!

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Edited by Luke May, Staff Editor

Luke is a seasoned editor with over seven years of experience. His passion for writing and storytelling started when he was a teenager, spending countless hours reading books and creating his own stories.

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