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types of audio compressors.

Types Of Audio Compressors: From VCA To Optical And Beyond

February 17, 2024 
Last Updated on February 17, 2024

One of the most powerful tools at an audio engineers disposal is a device called a compressor. A compressor, which comes in hardware and plugin options, makes the quiet parts of an audio signal louder and the loud parts tamer. But did you know are there are actually several types of audio compressors, each with their own special sound flavor? In this post, we'll dive into the world of compressor types, like VCA, FET, and even optical ones (yes, like the kind in your glasses!). So buckle up and get ready to learn how to choose the perfect compressor to make your music sound like a million bucks!

What Does An Audio Compressor Do?

Audio compression with gain reduction LEDS going in increments of 3.

The main function of a compressor is to even out volume. It takes the loudest and softest parts of a track and brings them closer together. This is done using the following parameters which are at the heart of how a compressor works:

  • Threshold: This sets the level at which the compressor starts working. Signals below this level are left untouched, while signals exceeding it get compressed.
  • Ratio: This determines how much the signal is reduced after exceeding the threshold. A higher ratio means more reduction, resulting in a more compressed sound.
  • Attack: This controls how quickly the compressor reacts to a signal exceeding the threshold. A faster attack time clamps down on loud sounds instantly, while a slower attack allows for more natural transients.
  • Release: This determines how quickly the compressor returns to normal gain after the signal falls below the threshold. A faster release bounces back quickly, while a slower release lets the gain decrease more gradually.

By adjusting these parameters, you can fine-tune the compressor to achieve the desired effect on your audio.

4 Main Types Of Audio Compressors

Now that you understand the essential function and controls of a compressor, let's delve into the four different types. Each compressor type utilizes unique technology, resulting in distinct sonic characteristics that impact the sound in various ways.

VCA (Voltage Controlled Amplifier)

SSL Bus VCA compressor.

VCA compressors rely on electrical circuits to manage gain reduction. They are great at quickly and precisely adjusting the volume of a track. VCAs are known for their clean, transparent sound, preserving the natural character of the audio. They offer fast attack times, making them ideal for tight and punchy compression, often used on drums, vocals, and bass.

FET (Field Effect Transistor)

1176 FET compressor.

FET Compressors use a special gadget called a Field Effect Transistor (FET), similar to tiny electronic switches, to control gain. These compressors are known for their aggressive character, adding warmth and smooth compression with a distinct punch. FET compressors are popular for taming electric guitars, adding bite to vocals, and shaping the overall punch of a mix. Their fast attack times are perfect for capturing transients while adding subtle color.

Optical Compressor

LA-2A optical compressor.

Optical compressors use light-dependent resistors to adjust gain. Imagine a light-sensitive element acting like a photocell, controlling the volume based on the intensity of the incoming signal. An Optical Compressor watches this light and, as it brightens, it softly turns down the volume, keeping everything smooth and pleasant to listen to. Optical compressors are renowned for their smooth and gentle compression, often described as musical. They excel at handling dynamic instruments like bass and piano, preserving their natural character while taming unruly peaks.

Vari-Mu Compressor

Vari-Mu compressor.

Vari-Mu compressors, also known as tube compressors, employ vacuum tubes to manipulate gain. These tubes add warmth, richness, and a subtle harmonic distortion, reminiscent of classic analog recordings. Their name comes from "Variable Mu," where "Mu" means gain in the world of electronics. Vari-Mu compressors are sought after for their smooth character and vintage warmth, often used on vocals, buses, and for overall mastering applications to glue a mix together.

Choosing The Right Compressor Type

With an understanding of different compressor types and their sonic characteristics, you now are capable of choosing the right compressor for your application. Here are some key factors to consider:

1. Application:

  • Instrument or vocal: Different instruments and vocals benefit from specific compressor types. For example, VCAs excel on drums and bass, while FETs shine on guitars and vocals.
  • Desired sound: Do you want transparent compression to preserve natural character, or are you seeking warmth, punch, or vintage vibes?

2. Budget:

Compressors range in price from affordable plugins to high-end hardware units. Consider your budget and explore options that fit your needs and financial constraints.

3. Hardware vs. Software:

Both hardware and software compressors offer various functionalities. Hardware units may provide a more tactile experience with true analog circuitry, while software plugins offer versatility and affordability.

Remember: Experimentation is key! Don't be afraid to try different compressor types and settings on your music. Listen closely to their impact and choose the one that best complements your audio and achieves your desired sound.

Related Article: Compressor Cheat Sheet | The Only Guide You'll Ever Need!

Frequently Asked Questions (FAQs)

How do I set up a compressor?

Setting up a compressor involves adjusting a few key parameters: threshold, ratio, attack, release, and make-up gain. The threshold sets the volume level at which the compressor starts working. The ratio determines how much compression is applied once the threshold is exceeded. Attack controls how quickly the compressor reacts to exceeding the threshold, while release sets how quickly it stops compressing after the volume drops below the threshold. Make-up gain allows you to boost the overall signal to compensate for the volume reduced by compression.

Can I use more than one type of compressor on a track?

Absolutely! Many engineers use a combination of compressors to shape the sound. For example, you might use a FET compressor for its quick response on a vocal track, followed by an Optical compressor for its musicality and smoothness.

Do I need a hardware compressor, or can I use software?

While hardware compressors have their charm and sonic characteristics, software compressors are highly versatile and can emulate the behaviors of various hardware models. The choice depends on your workflow, budget, and the sound you're aiming for.

When should I apply compression in my music production process?

Compression can be applied during recording (tracking), mixing, or mastering. During tracking, it can help manage levels and protect against clipping. In mixing, it shapes the dynamics of individual tracks or buses. During mastering, it ensures the final mix has a consistent volume level and dynamic range.

What's the difference between a limiter and a compressor?

A limiter is a type of compressor with a very high ratio, typically starting at 10:1 and going up to infinity:1, which effectively means any signal above the threshold is limited to a certain level. While compressors gently manage dynamic range, limiters are used to prevent audio from peaking above a certain point, protecting against distortion and clipping.

Final Thoughts

Compressors might seem like fancy gadgets, but they're actually pretty cool tools that can help your music sound smoother, punchier, and more polished. They are a necessity in achieving high-quality mixes that translate between different playback devices. Now that you know about the different types of audio compressors and how to choose the right one, you're ready to experiment and find the perfect one for your sound!

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