3 Common Types of Audio Compressors


The Vari-Mu compressor, also known as a tube compressor, is a type of analog compressor that was first developed in the 1950s. The name “Vari-Mu” comes from the fact that the compression ratio of the device can vary, as opposed to fixed-ratio compressors.

Vari-Mu compressors are characterized by their smooth, warm, and musical compression characteristics, making them particularly popular in professional audio recording studios for dynamic control of vocal and instrument recordings. The design of a Vari-Mu compressor typically consists of a vacuum tube amplifier circuit, with a gain reduction element that varies the gain of the amplifier in response to the input signal level. This design results in a unique and musical sound that has become sought after by audio engineers and producers.

The origin of the Vari-Mu compressor can be traced back to early experiments with vacuum tube circuits for audio signal processing. The first commercially available Vari-Mu compressors were manufactured by companies such as Altec Lansing and Fairchild in the 1950s, and the technology has continued to evolve and be refined over the decades since.

Today, Vari-Mu compressors are still widely used in professional audio recording studios, and many modern recreations and interpretations of the classic designs are available from a variety of manufacturers. One of the most popular being the Manley Vari-Mu.

In my studio, I use use a design by Bergman Labs out of Sweden.

Bergman Vari-Mu


The concept of a voltage-controlled amplifier (VCA) compressor has its roots in analog sound recording and mixing technology. The first VCA compressors were developed in the 1970s and were widely used in the recording industry to control the dynamic range of audio signals.

A VCA compressor works by using a voltage-controlled amplifier to adjust the gain of an audio signal in real-time based on the level of the input signal. This allows the compressor to reduce the dynamic range of the audio and make the quiet parts louder and the loud parts quieter. The VCA compressor is widely used today in many different types of audio equipment, including mixing consoles, recording studios, and live sound reinforcement systems.

In the analog era, VCA compressors were implemented using analog circuits, but today they are often implemented using digital signal processing algorithms in digital audio equipment. Nevertheless, the basic concept of using a voltage-controlled amplifier to control the gain of an audio signal remains the same, and the term “VCA compressor” is still commonly used to describe this type of compression technology.

TK Audio BC1-THD


The FET (Field-Effect Transistor) compressor is a type of audio compressor that uses Field-Effect Transistors (FETs) as its gain-reducing element. The exact origin of the FET compressor is not known, but it is believed to have been developed in the 1960s, when FETs were first introduced as a replacement for vacuum tubes in audio equipment.

FETs have a unique characteristic compared to other gain-reducing elements, such as vacuum tubes or operational amplifiers, that makes them well suited for use in compressors. They have a fast response time and a smooth, natural sound that has made them a popular choice for use in a variety of audio applications, including mixing consoles, outboard gear, and guitar amplifiers.

Over the years, the design of FET compressors has evolved, and many different variations of the basic concept have been developed. One of the most popular FET compressor designs is the Urei 1176. Today, modern FET compressors like the Chandler Germanium continue to be widely used by audio engineers, producers, and musicians alike, and they are considered an essential tool in the recording studio.

Chandler Limited Germanium Compressor

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Preparing Your Songs For Mastering

Preparing your song for mastering can be a confusing process. Especially with the vast amount of information out there. Here are some tips that help me give you the best possible Master for your music.

What sample rate and bit depth do I render my song to?

You should render (or bounce) your song to whatever sample rate you were using in your session. Whether it’s 44.1 kHz, 48 kHz or 96 kHz, it doesn’t matter. I recommend not changing the sample rate and let me complete the final down sampling to 44.1 kHz. If you need your Master delivered at a higher quality sample rate, just let me know.

The same goes for bit depth. In my opinion, the dithering process should only be done once. Again, whether you send it in 32, 24 or 16 bit, it doesn’t matter. Just keep it at the original sample rate and bit depth.

So what is the optimal file?

For file types, you can send in a .WAV or .AIFF file. I prefer a stereo interleaved file. Please do not send MP3s or any “compressed” file.

How loud should the song be?

Ideally, I would like approximately -6db of headroom. On your master fader, here’s what -6db looks like:

Ableton Master Channel

Do I need to remove all processing from the Master Channel?

I would prefer that you remove all processing from the Master Channel. The reason being is that if you have things like EQ, Compression and Limiting on your Master Channel, it really limits the processing I’m able to do on my end.

However, if you feel that your bus compressor adds a distinct character to the song, then by all means leave it on. Just send me a note with details on the processing you’ve put on the Master Channel.

Or, another option is to send two files. One with the processing on and one with the processing off.

Naming your files.

This is often overlooked, but makes a huge difference. Ideally, a good file name will look like this:

Artist Name – Song Name (Original Mix) – 125BPM – Premaster

If at all possible, please list the tempo or BPM of your song in the file as well.

Make sure your Mix is ready.

This should go without saying however, please make sure your mix is ready. Does the placement of your kick drum in relation to the bass sound good? Are the high hats at the right level? Do the vocals sit right in the mix? Having a good mix is the first and by far the most important step in the process.

The rule of thumb is this… If the mix isn’t good, the final master will not be good. I can’t stress that enough.

If you want me to listen to the mix beforehand, by all means, please send it over. My role is to be of service and my goal is to help your music sound as best as possible.