5 Types of Equalizers – Part One – FixATune.com

5 Types of Equalizers – Part One – The Program Equalizer

There are Fixed Band Equalizers and there are Variable “Q” Equalizers. There are EQ’s that are optimized for Mixing and there are EQ’s that are perfect for Mastering. There are EQ’s that we typically use on individual tracks and there are EQ’s that we like to save for Bus Mixing and Master Outputs.


Five Types of EQ

The five primary categories of EQ’s I will define here are:

Program Equalizers, Mix EQ’s, Mastering EQ’s, Console EQ’s, and Outboard EQ’s.

The first thing to know about these EQ types is that they can overlap. Many Program Equalizers are used for Mastering and for Mixing, and most Program Equalizers are also Outboard EQ’s. Perhaps the mere amount of ‘crossover’ (pardon the pun) contributes to the confusion that surrounds the deciding factors in the best EQ’s to use for a given job. I also consider the corresponding cost affixed to EQ types a confusing factor when deciding on the best EQ’s for a given job.

Let’s go ahead and assign a description to each of these five distinct EQ types, starting with the Program Equalizer.

The Program Equalizer is a type of EQ that is most famous for the Pultec-style EQ. The Program Equalizer provides a wide range of options and frequencies, and is defined by its usefulness on a wide range of “Program Material.”

Program Material is defined as main tracks, or final audio sources, that are used for programming, whether they are pre-recorded audio masters of music content, or a live broadcast program that is output to a radio frequency band, television transmission, or, in our modern world, for an internet stream. Program Material is the final combined output of a professional sound source.

In song or in album form, Program Material is the final song track that has been mixed and mastered, or it is the entire album made of a combination of songs. In Broadcast,  the Program Material has traditionally been the primary voice content of the Broadcast, but has included musical performances, events, and a limitless range of Programming.

Historically, the Program Equalizer was designed to provide the Audio Engineer immediate access to Frequencies they might need to adjust in order to improve the clarity and professional quality of voice content. Since the sound range attributed to voice content, and the final Frequency output transmission of early Broadcasts was typically around 12kHz Maximum, Frequencies typically were rounded off at around 15kHz, tapering down 5dB every 1000 cycles or so until they reached above 20,000 Hz where they were further reduced.

These extremely high Frequencies would not contain material that could be correctly reproduced over the air, and leaving these in the signal could cause a build-up of interference and cause unwanted transmission and reproduction issues. Optimizing the signal for the Frequencies that could be reproduced accurately was the strong point of the Program Equalizer.

The Program Equalizer has been around at least since the late 40’s in their current form that we still use today, but it’s use has changed over the years. One thing that has distinguished it from other Mastering Equalizers is the fact that it is typically a Mono device. The highest quality Program Equalizers can be matched to each other so that they are useful as a Stereo pair for modern mixing and mastering use. The fact that these EQ’s are typically Mono is due to the fact that all early primary recording sources were also Mono. Radio programs were Mono, as were early recordings. In the 1940’s through the 1950’s, and even part of the 1960’s,  the audio spectrum was controlled to limit the high Frequencies above 15,000Hz and to tailor the mid and upper Frequencies with a wide range of quickly accessible controls, along with the ability to enhance broad ranges of lower Frequencies while focusing on reducing boominess and muddiness that could affect clarity in Broadcast and recording. Increasing the gain in upper frequencies could remain smooth and articulate because the slope reduced anything above 15kHz that was not going to be transmitted, and would not typically translate to earlier recordings.

In the late 1950’s and into the 1960’s, the quality of Program Equalizers was well known, but its usefulness expanded as the range of capabilities of recording expanded. Stereo recordings led to the need to calibrate two independent Program Equalizers that could operate together, balancing the left and right channels of recordings, but also the ability to control the bass Frequencies in the center of a mixed recording was necessary for controlling needle movement on a record player. As High Fidelity recordings grew closer to our modern full-range listening experience, many Program Equalizers, along with other recording devices, leaned more and more towards a full-range capability. No longer were there filters intentionally designed to buffer out extended high Frequencies, but rather they were designed to make a ruler flat response.

Still, the incredible quality of earlier Program Equalizers were recognized for their detail and this has continued in modern day use, where we find it is possible to simply boost more high Frequencies with early Program Equalizers, since the cut slope that occurs above 15kHz tends to simply reshape high Frequencies into a Bell-Shaped curve instead of a flat Shelf-response. The exact same lines of Program Equalizers, like the classic Pultecs that we still use every day in modern studios, both in their real hardware form and as software equalizers,  exist in their original form and more often in the form of the flat response in extended Frequencies. They are used for individual tracks, bus groups, final mixdown, and for mastering. They are ideal for individual vocal tracks, since the original Program Material focused mainly on vocals, but the high quality sound and structure in design of Frequencies is useful on literally any sound source that needs fixing or enhancing.

An example of a typical Program Equalizer would include a combination of a Low Cut filter, Low Boost and Cut Frequencies with Gain control, a wide range of Mid Frequencies, with or without a “Q” Width control, High Frequencies, typically using fixed Width and boost and cut Gain, although some only have one grouping for boost or cut, and potentially a High cut filter, and often they alternately contain High and Low Shelf EQ’s. I will go into detail about these different type of filter options in a later Post.

As you can see, the history of the Program Equalizer has changed over the years alongside the changes that have occurred with actual Program Material. We have AM and FM Radio, Digital Radio, Internet Broadcasting, Digital Cable and Satellite Television, DVD’s, Blu-Rays, and new content formats coming every year. The Program Equalizer seems to hold its own with amazing analog sound through every transformation our technological audio world experiences.