Category: Mixing and Mastering

Basics of Mixing – 6.3 Types of Compressors

Hello, this is Jooyoung Kim, an engineer and music producer.

Today, we will discuss the different types of compressors based on their operating principles.

Before we begin, it’s important to note that most compressors we talk about today are named after the specific components used as attenuators in each type. These components give each type its unique characteristics, so understanding these classifications is essential.

Shall we get started?

1) Variable-Mu (Vari-Mu)

Vari-Mu compressors use vacuum tubes as attenuators. (Note that just because a compressor has vacuum tubes doesn’t automatically make it a Vari-Mu compressor.)

“Variable” means adjustable, and “Mu” (μ) stands for gain. So, Variable-Mu essentially means variable gain.

This might sound confusing, but essentially, as the input signal increases, the current to the vacuum tube’s grid decreases, thus varying the output level and creating adjustable gain.

Vari-Mu compressors have a non-fixed ratio and typically feature a soft knee. They also impart significant coloration to the sound due to the nature of vacuum tubes.

Famous examples include the Fairchild 670, Manley Variable Mu, and Chandler Limited RS124. These were predominantly used in the early days of compressors.

2) Optical (Opto)

Opto compressors use an optical isolator (photo transistor) as the attenuator. The intensity of the light changes according to the input signal, which in turn adjusts the compression. The release time varies significantly depending on the amount of compression.

A well-known Opto compressor is the LA-2A, which was also called a 2-step compressor due to the significant difference in reduction levels around -3dB. This characteristic makes it popular for vocal sources.

Both vacuum tubes and transistors can be used for gain control in Opto compressors. For instance, the LA-2A uses vacuum tubes, while the LA-3A replaced these with transistors.

The Tube-Tech CL1B is another common Opto compressor found in studios.

3) Solid State

Solid State compressors use transistors or diodes as the attenuators. When transistors first became available, they replaced vacuum tubes due to their lower power consumption and smaller size.

The UA 1176 is a prime example and remains one of the most famous Solid State compressors. It is known for its very fast attack and release times. The Blue Stripe version of the 1176 is especially noted for its strong coloration, making it a favorite for drum sources.

4) Diode Bridge

Diode Bridge compressors use a diode bridge circuit for signal attenuation. These became popular in the 1960s for their faster response compared to typical Opto compressors and lower distortion compared to many FET designs.

Notable examples include the Neve 33609, 2254, Chandler Limited Germanium, and EMI TG12345.

5) VCA (Voltage Controlled Amplifier)

VCA compressors use a Voltage Controlled Amplifier as the attenuator. A VCA adjusts the amplification based on the input signal’s voltage, allowing precise control over the input signal level. VCA designs typically have low distortion and less coloration compared to Vari-Mu, Opto, and Solid State compressors.

The dbx 160 is a representative VCA compressor, along with the Amek 9098 Compressor Limiter, SSL G Compressor, API 2500, Vertigo VSC-3, and Shadow Hills Mastering Compressor (excluding the Opto section).

6) PWM (Pulse Width Modulation)

PWM compressors use pulse width modulation to control signal strength. They can turn on and off in less than 1 nanosecond, making them extremely responsive with even less distortion than VCA compressors.

Famous PWM compressors include the Crane Song STC-8 and the Pye 4060 and 5060.

7) Digital

Digital compressors are not replicas of analog compressors but are designed to detect the signal level in real-time and apply compression based on the set threshold and ratio.

Digital compressors may introduce harmonic distortion due to nonlinear responses and aliasing, although many modern plugins mitigate aliasing with oversampling.

Despite potential distortion, digital compressors typically have less coloration and are cleaner than analog counterparts. Most basic DAW compressor plugins fall into this category.

Conclusion

Nowadays, most compressors used are plugins. Even if they replicate the same vintage hardware, their characteristics can differ, making memorizing all these details unnecessary.

When purchasing or using a compressor for the first time, it’s helpful to understand its operating principle to get a rough idea of its characteristics.

Also, remember that digital replicas may still suffer from aliasing issues. The only way to completely avoid this is by using the actual hardware.

That’s it for today. See you in the next post!

Basics of Mixing – 6.2 Compressor Operation Principles

Hello, this is Jooyoung Kim, an engineer and music producer.

Today, we’ll discuss the basic principles of how a compressor works.

A compressor is a device that reduces sounds exceeding a set volume threshold by a certain ratio.

You can set how quickly the compressor reacts when the sound exceeds the threshold (Attack) and how quickly it stops compressing when the sound drops below the threshold (Release).

The four basic parameters of a compressor are Threshold, Ratio, Attack, and Release. By making louder sounds quieter and leaving quieter sounds as they are, a compressor helps to level out the volume.

Compressed sounds tend to become quieter. Therefore, to match the volume back to the original level, you use the Output Gain parameter.

Many compressor plugins have an Auto Gain feature that automatically adjusts the volume, but in my experience, none of them have worked well enough. So, if your compressor has an Auto Gain feature, it’s best to turn it off.

Another setting to consider is the Knee. Hard Knee means the compressor kicks in immediately once the threshold is exceeded, while Soft Knee allows for a more gradual compression as the sound approaches the threshold.

This covers the most basic operation and usage of a compressor.

However, just explaining the parameters and telling you to try them out isn’t enough guidance, right?^^;;

For example, the classic compressor LA-2A has a fixed ratio of 4:1.

Similarly, most versions of the 1176 compressor (excluding the AE version) start with a minimum ratio of 4:1. Starting around these settings can be a good approach.

The appropriate threshold setting varies greatly depending on the desired effect. If you’re new to this and have no idea where to start, try aiming for a Gain Reduction of around -3dB.

Other considerations include:

  1. Setting a fast Attack can change the transient feel of the sound, affecting the instrument’s groove.
  2. Setting a fast Release can cause the sound to pump as it recovers quickly.

Each instrument and sound source is different, so there’s no one-size-fits-all guide. Additionally, many compressors include saturation, which adds coloration to the sound, so various factors need to be considered.

Still, it’s important to start experimenting! By testing out different compressors, you’ll begin to understand which settings work best in different situations.

In the next post, we’ll look at the different types of compressors. Understanding their characteristics will give you a better grasp of how to use them effectively.

See you in the next post!

Basics of Mixing – 6.1 Compressor

Hello, this is Jooyoung Kim, an engineer and music producer.

Today, I’d like to talk about compressors.

Why do we use compressors in mixing?

First, the most fundamental role of a compressor is to level the dynamics.

When the dynamic range (the difference between the loudest and softest sounds of an instrument) is large, it can cause issues where vocals or individual instruments are not clearly heard. It can also result in instruments sounding like they are moving forward and backward in the mix when listening through speakers. By controlling dynamics well, it becomes easier to increase the overall loudness during mastering.

Second, compressors can change the groove of the music.

Depending on when the compressor kicks in and out, and how it compresses, it can alter the groove of the instrument source.

Third, compressors can change the tone of the source through saturation.

Based on the harmonic distortion and frequency response characteristics of the compressor, it can add different textures to the original source.

Fourth, compressors can provide a sense of unity.

A compressor applied to a bus can impart its unique saturation and groove to the entire group of instruments, helping them blend well together.

For these various complex reasons, we use compressors.

In this sixth chapter of Mixing Basics, we will cover:

  1. How to use a compressor
  2. Types of compressors based on their operating principles
  3. Noteworthy compressors
  4. Various other dynamic processors (decompressors, expanders, gates, de-essers, multiband compressors, etc.)

In the next post, we’ll start by discussing how to use a compressor.

Basics of Mixing – 5.4 Phase Issues in EQ

Hello, this is Jooyoung Kim, an engineer and music producer.

Today, I’d like to discuss a crucial aspect to consider when adjusting EQ: phase issues.

The image above shows the phase change graph when using the Brickwall feature in Fabfilter Pro Q3.

Phase change is generally represented as a continuous line. However, when drawing the graph continuously, the size becomes too large, so the vertical range is usually set to 2π, and the line continues from the top or bottom when it breaks. It’s quite difficult to explain in words.

Anyway, considering such factors, the jagged phase changes can still significantly affect the sound. Extreme phase changes can make the sound seem as if an unintended modulation effect is applied, so it’s important to use it carefully.

Because of these issues, Linear Phase EQ was developed. Linear Phase EQ does not cause phase issues. However, it introduces a phenomenon known as Pre-Ringing.

  • Pre-Ringing Phenomenon

Pre-Ringing occurs when using Linear Phase EQ, causing the sound to ring before the waveform. Try bouncing your track using Linear Phase EQ. As shown in the image above, you’ll notice a waveform appearing at the front that wasn’t there originally.

Other than digital EQs, many plugin emulations of analog EQs alter the phase and frequency response graphs just by being applied.

For instance, consider the commonly used Maag EQ4 for boosting high frequencies.

On the left is the frequency response graph when only the Maag EQ4 plugin is applied without any adjustments, and on the right is the phase change graph under the same conditions.

Here’s what we can deduce about using EQ:

  1. Applying an EQ can change the basic frequency response from the start.
  2. Non-Linear Phase EQs will inevitably cause phase changes.
  3. Linear Phase EQs can introduce Pre-Ringing, creating new sounds that were not there originally.
  4. EQ plugins or hardware with Harmonic Distortion can add extra saturation to the sound.

Understanding these points is crucial when adjusting EQ.

Of course, there are many excellent engineers who achieve great results without knowing all these details. Ultimately, the most important thing is that the sound comes out well, regardless of understanding the underlying principles.

However, I personally feel more comfortable when I have a solid understanding of the fundamentals. So, knowing this information can never hurt.

That’s all for today. I’ll see you in the next post!