The Birth of the Parametric Equaliser
September 23, 2024
A parametric equaliser is a powerful audio tool used to precisely shape and sculpt sound by adjusting frequency, bandwidth, and gain. Unlike traditional tone controls like the Baxandall circuits found on vintage stereo systems, which offer simple bass and treble adjustments, a parametric equaliser provides more flexibility and control over specific frequency ranges. This makes it ideal for tackling problem frequencies and fine-tuning audio. In contrast to graphic equalisers, which typically feature a fixed set of bands (often 30, covering one-third of an octave each), a parametric equaliser allows you to choose the exact frequency you want to affect, as well as the width of the affected range. This versatility makes parametric equalisers the go-to tool for professionals looking for precise, targeted audio adjustments. The concept of the parametric equaliser was not only revolutionary, but at the time, many believed it was impossible to create such a device.
the father of the Parametric EQ
George Massenburg
George Massenburg, an acclaimed audio engineer, is credited with developing the parametric equaliser in the late 1960s. The story of how he came up with the idea starts with his time as a student at Johns Hopkins University, where he was deeply involved in electronics and sound engineering.
At the time, audio engineers used graphic equalisers or basic tone controls like Baxandall circuits to shape sound. These tools had limitations, offering only fixed frequency bands for adjustment or limited control over frequency and bandwidth. Massenburg, while working on music recording and live sound, became increasingly frustrated with these limitations. He realised that a more flexible tool was needed, something that would allow engineers to not only adjust gain (volume) at specific frequencies but also have control over which frequencies were being affected and how wide the range of those frequencies could be.
In 1969, while working in a recording studio in Baltimore, Massenburg started to conceptualise the idea of a fully variable equaliser. He imagined a device where the user could dial in any frequency, adjust the bandwidth (Q), and control the gain – something no other equaliser could do at the time. This idea was groundbreaking because, up until then, most people believed that such precise control over audio frequencies in a single device wasn’t possible.
Massenburg’s breakthrough came when he applied the principles of filter design to his problem. He began experimenting with circuits and developing the first prototype of what would later become the parametric equaliser. By using variable capacitors and resistors, he was able to achieve a design that allowed continuous adjustment of both frequency and bandwidth, effectively creating the first parametric equaliser.
Massenburg debuted the parametric equaliser in 1972 at the AES (Audio Engineering Society) convention in Los Angeles. The industry quickly recognised its potential, and the parametric equaliser soon became a key tool in studios and live sound environments. Over the years, Massenburg continued to refine and develop his designs, contributing to the advancement of professional audio tools.
Today, the parametric equaliser remains a fundamental part of modern audio processing, and Massenburg’s invention is still regarded as a major milestone in audio engineering.
The Stairwell at The Power Station Studios in New York, famous for its lush reverb.
The first commercially available Parametric Equaliser
ITI MES-430 Parametric Equaliser
The ITI MES-430 Parametric Equaliser is a revolutionary audio tool, marking the first commercially available parametric equaliser. Developed by George Massenburg, it introduced unprecedented control over frequency, bandwidth, and gain, transforming the way sound could be shaped. With its innovative design, once thought impossible, the MES-430 set the benchmark for modern equalisation, delivering precise and transparent sound shaping.
Its impact is still felt today, with musicians, producers, and engineers appreciating its flexibility and effectiveness across various audio tasks. Originally designed for mastering, the MES-430 quickly became indispensable in studios for all types of equalisation. Its versatility established parametric equalisation as an industry standard, making it a foundational tool in professional sound design. These original equalisers are incredibly valuable and fetch a high price on the rare occasion they come up for sale.
The ITI MES-430 Change Equalisation in professional audio forever upon its release.
How Do Parametric Equalisers Compare to other EQs and what is it that makes them unique?
What sets a parametric equaliser apart from its predecessors?
To answer that, we first need to look at how earlier equalisers functioned, starting with one of the simplest, the Baxandall equaliser.
The most common equalisation
Baxandall Equaliser
A Baxandall EQ is a type of shelving equalizer designed by the English electrical and audio engineer Peter J. Baxandall in 1950. It’s commonly referred to as a tone control, and if you recall the “bass” and “treble” knobs on older hi-fi systems, they were likely Bax filters in action. These controls were usually a 100Hz bass control, and 10kHz treble control. What makes these filters unique? The key lies in the shape and slope of the high and low shelf filters in a Baxandall EQ.
Baxandall shelves have a broad and gentle Q-factor, giving them two standout characteristics. First, phase shift is reduced and spread more evenly compared to standard parametric shelves. Second, within their usable frequency ranges, most of the affected audio frequencies lie within the rising or falling sections of the Baxandall EQ curve. By the time the curve flattens out, it’s at frequencies beyond human hearing.
Together, these features make Bax shelves sound transparent and musical. What works well in a home stereo system doesn’t always translate to professional audio, especially when it comes to precise tone shaping. However, Baxandall EQs excel as a tool for broad, subtle tone enhancement.
And then came the...
Graphic Equaliser
A graphic equaliser is a type of audio equaliser that allows control over a series of fixed frequency bands, typically using sliders to adjust the gain (boost or cut) for each band. The term “graphic” refers to the visual representation it provides: as you move the sliders, the EQ curve is graphically shown by their positions, giving a clear picture of the tonal changes being made.
A standard graphic equaliser divides the audio spectrum into a specific number of frequency bands, often ranging from 5, 10, 15, or up to 31 bands. Each band focuses on a set frequency, and the user can increase or decrease the gain for that particular range. For example, in a 31-band graphic equaliser (also known as a 1/3-octave EQ), the audio spectrum is split into narrow bands, often covering the full range of human hearing from 20Hz to 20kHz. Some graphic equalisers might have fewer bands, such as 10, offering broader ranges for each slider.
The sliders on a graphic EQ control the gain of each frequency band, with upward movement boosting the gain and downward movement cutting it. Gain is typically measured in decibels (dB). However, the key feature of a graphic equaliser is that the centre frequencies of each band are fixed, meaning you can only adjust the gain, not the frequency itself. Changing the sliders alters the tonal balance of the audio. For instance, boosting the lower frequencies enhances the bass, while cutting higher frequencies can soften treble, creating a warmer, less bright sound.
Graphic equalisers are easy to use because the sliders provide a clear, visual way of shaping the sound. They are often used in live sound setups, car audio systems, and consumer equipment, where quick adjustments are necessary.
The differences between a graphic equaliser and a Baxandall EQ mainly lie in how they manage frequency control, precision, and application. A graphic equaliser has fixed frequency bands with a dedicated slider for each band. While you cannot change the centre frequency, having many bands (such as in a 31-band EQ) allows you to shape the sound across the entire frequency range. In contrast, a Baxandall EQ usually has just two or three controls, typically for bass and treble shelves, enabling broad tonal shifts in the low and high frequencies, such as 100Hz and 10kHz. However, it lacks the precision to adjust individual frequencies or the midrange with the same accuracy.
In terms of precision, a graphic equaliser, particularly one with 31 bands, provides much finer control over the frequency spectrum. You can target specific parts of the audio spectrum, making it ideal for detailed tone shaping or corrective EQ. A Baxandall EQ is less precise, offering smooth and broad adjustments with a gentle curve that affects a wide range of frequencies simultaneously, making it better suited for overall tonal adjustments rather than pinpoint fine-tuning.
The use cases for these equalisers also differ. Graphic equalisers are often used in live sound environments, studio settings, and audio systems where exact frequency spectrum adjustments are needed. They are particularly useful for addressing specific problem frequencies or for shaping sound in a detailed manner. In contrast, Baxandall equalisers are typically found in older hi-fi systems or used where broad tonal adjustments are desired. Known for their musical and transparent sound, they are ideal for sweetening a mix or making subtle tone changes without impacting specific frequencies too heavily.
In terms of EQ curve shape, a graphic equaliser provides a more linear, “stepped” visual representation, with each band being adjusted individually. In contrast, a Baxandall EQ produces a smooth, sweeping curve due to its wide, gentle Q factor. The low and high shelves gradually affect large parts of the spectrum, resulting in less abrupt tonal changes compared to the distinct frequency bands of a graphic equaliser.
“A graphic equaliser offers much more precision and control over individual frequency bands, making it ideal for detailed adjustments. In contrast, a Baxandall EQ is simpler, providing broad, smooth adjustments over the low and high ends of the spectrum, which is ideal for general tone shaping rather than detailed corrective work. While a graphic EQ is often used in professional audio settings, a Baxandall EQ is known for its musicality and is favoured for its natural, transparent sound.”
DBX continues to produce a range of graphic equalisers, which are mainly used in live sound systems to correct room acoustics and address problematic frequencies in the various venues on a tour.
The Legendary
Pultec Equalisers
The Pultec equaliser is renowned for its distinctive sound and simplicity, making it a favourite in both vintage and modern studio settings. It stands out not only for its unique circuit design but also for the musicality and warmth it imparts to audio, even without significant EQ adjustments. Let’s dive into what makes it so special and how it differs from a Baxandall and graphic equaliser.
The Pultec EQ’s passive circuit design relies on inductors, capacitors, and resistors to shape the frequency response, rather than using an active amplifier to boost frequencies. This passive approach results in minimal phase distortion, giving the EQ a natural and musical sound. Many engineers are drawn to the Pultec for the warmth it imparts to audio, even when no significant boosting or cutting is applied. This characteristic warmth comes from the interaction between the EQ’s passive components and the valve (tube) amplifier that follows, which adds harmonic richness and smoothness.
One of the Pultec EQ’s standout features is its ability to simultaneously boost and cut the same frequency, particularly in the low end. This allows the EQ to boost a broad range while cutting a narrower band, resulting in a controlled yet full low-end sound. This technique helps tighten up the bass while still maintaining its warmth and size.
The controls of a Pultec EQ, such as the EQP-1A, are simple but highly effective. With basic bass and treble sections for boosting and cutting, alongside additional high-frequency controls for bandwidth and boosting, it delivers smooth, musical results far greater than its straightforward design suggests. Lastly, the Pultec is praised for its smooth handling of high frequencies. It can boost the treble in a transparent and gentle way, avoiding the harshness that can be introduced by other equalisers, resulting in a clean, refined high-end response.
In terms of control and frequency range, the Pultec EQ offers a more selective and musical approach with fewer controls. Its bass and treble bands are focused on broad tonal shaping, and it’s famous for allowing simultaneous boosting and cutting in the low-end, which is more about tonal enhancement than precision adjustments. The Baxandall EQ is also designed for broad and smooth tonal shaping, but it typically features fixed bass and treble shelves, making it less flexible than the Pultec. It’s excellent for overall tone adjustments but lacks the Pultec’s unique ability to boost and cut at the same time. Meanwhile, the graphic EQ provides the most detailed control with individual sliders for fixed frequency bands. It’s built for precision, enabling fine adjustments across specific frequency ranges, unlike the broader approaches of the Pultec and Baxandall.
Regarding tone and character, the Pultec EQ is known for adding warmth, depth, and a pleasing tonal quality, even without much boosting or cutting. The valve circuitry in many Pultec units contributes to its rich and smooth sound, making it ideal for enhancing the overall tone of a mix. The Baxandall EQ, while also smooth and musical, doesn’t provide the same degree of warmth or character as the Pultec. It’s more transparent and clean, typically used in consumer audio systems or for general tone shaping. On the other hand, a graphic EQ doesn’t add any inherent tone or character. It’s neutral and functional, designed for precision and mainly used for corrective purposes like dealing with room acoustics in live sound.
In terms of use cases, the Pultec EQ is primarily found in studio settings for mixing and mastering, where its tonal enhancement abilities are valued for adding warmth and colour to individual tracks or entire mixes. The Baxandall EQ is commonly used in hi-fi audio systems or as a broad tone control in mixing, where it provides smooth, musical adjustments without precise frequency control. It’s ideal for sweetening the overall sound but not suited for pinpoint accuracy. A graphic EQ is most often used in live sound and studio environments when detailed, corrective EQ is needed. It’s perfect for addressing specific problem frequencies or fine-tuning a mix’s overall balance, but it’s not typically used for tonal enhancement.
As for sonic transparency, the Pultec EQ is known for adding warmth and character to the sound, which is part of its appeal. It’s not transparent, but that’s why it’s highly regarded in music production. The Baxandall EQ is known for its transparency and smoothness, making it ideal for broad adjustments without colouring the sound too much. A graphic equaliser, meanwhile, is neutral and transparent by design, focusing on precision without adding warmth or character to the sound.
“The Pultec equaliser is revered for its ability to add warmth, depth, and smooth tonal enhancement to audio, with its unique design allowing for both broad adjustments and musical shaping of frequencies. It differs from the Baxandall EQ in that it provides more character and flexibility, especially with its ability to simultaneously boost and cut frequencies. Compared to a graphic equaliser, the Pultec is far less precise but is unmatched in its ability to enhance the tone musically, whereas the graphic EQ is best for detailed, corrective work. Each EQ serves its own unique purpose, but the Pultec stands out for its musicality and sonic character.”
Pultec equalisers are still widely used around the world, not for their precision in tone shaping, but for the unique character they bring, adding a musical quality to the sound with every adjustment.
George Massenburg's Masterpiece
Parametric Equalisers
A parametric equaliser differs from a Baxandall, graphic, and Pultec equaliser in several key ways, particularly in terms of control, flexibility, and the kind of tone shaping they provide. Here’s a detailed comparison of how each type of EQ works and what makes them unique.
A parametric equaliser provides the most detailed control over the frequency spectrum by allowing you to adjust three main parameters for each frequency band. First, you can select the exact frequency you want to target, ensuring precise adjustments. Second, you have control over the gain, which lets you either boost or cut the level at that specific frequency. Finally, the Q-factor, or bandwidth, allows you to control the width of the frequency range being affected, enabling either narrow, surgical adjustments or broader tonal changes.
Visualising the Q-factor is key to understanding the power of a parametric equaliser. To the right (or below) are examples of a standard Q, a broad Q, and a narrow Q, demonstrating how the Q control influences the frequencies around the selected frequency, in this case, 500Hz.
Parametric equalisers are highly versatile, allowing you to adjust any frequency with precision, making them ideal for both corrective and creative applications. You can shape the sound with extreme accuracy, focusing on just the frequencies that need attention. Parametric equalisers are commonly used in studio settings, mixing, and mastering, where detailed frequency adjustments are needed. They are favoured for their precision and ability to address problem frequencies while preserving the overall sound quality.
Key differences in control can be seen across the various equaliser types. A parametric equaliser offers the highest level of control, allowing precise adjustments to frequency, gain, and Q-factor. In contrast, a Baxandall equaliser provides broad tone control with shelving filters that typically affect bass and treble frequencies.
A graphic EQ allows for adjustments across multiple fixed frequency bands, letting you boost or cut each one individually but without control over the Q-factor or centre frequencies. A Pultec equaliser, while offering fewer controls, has a unique ability to simultaneously boost and cut the same frequency, enabling distinctive tonal shaping.
In terms of flexibility, the parametric equaliser is the most versatile, allowing precise tone shaping and correction. A Baxandall equaliser is less flexible, designed for smooth and simple adjustments to the overall bass and treble. A graphic equaliser is moderately flexible, offering quick adjustments over many fixed frequency bands but lacking precision. Meanwhile, the Pultec equaliser is less flexible in terms of frequency control but is highly valued for its tonal colour and character.
Regarding tone and character, the parametric equaliser is transparent, focusing on exact tone shaping without adding any colour. The Baxandall equaliser offers smooth and transparent adjustments with a musical quality, though it doesn’t add much tonal character.
A graphic equaliser is neutral, typically used for corrective purposes rather than tone shaping, and doesn’t impart any character. The Pultec equaliser, however, is known for adding warmth and richness, with a unique tonal colour that enhances the musicality of the audio.
Each type of equaliser has its specific use case. A parametric equaliser is ideal for studio work, mixing, and mastering, where precise frequency control is crucial. Baxandall equalisers are best suited for hi-fi systems and broad stroke tone shaping in mixing contexts, where less precise adjustments are needed.
Graphic equalisers are commonly used in live sound and for room correction, where quick and easy adjustments to fixed frequency bands are essential. Lastly, Pultec equalisers are favoured in professional studios for their ability to add warmth and character to recordings, making them a go-to for tonal enhancement in mixing and mastering.
The 'Q' Factor
Bandwidth
Standard Q
Broad Q
Narrow Q
The highly regarded Maselec MEA-2 is clearly a descendant of the ITI MES-430 Parametric Equaliser
A parametric equaliser offers the most precise and detailed control, making it perfect for surgical tone shaping and corrective EQ. A Baxandall equaliser is designed for broad, smooth tonal adjustments, particularly in the bass and treble ranges. A graphic equaliser is useful for quick adjustments across multiple fixed frequency bands, typically in live sound environments. Finally, a Pultec equaliser stands out for its unique ability to shape tone in a musical and characterful way, adding warmth and richness, even with relatively simple controls. The term “surgical” perfectly captures the precision a parametric equaliser offers for tone shaping, making it ideal not only for mastering, where it truly shines, but also for tracking, where pinpoint corrections are essential for achieving the perfect guitar tone or vocal recording.
