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March 20, 2020

Pultec low end trick | Fab Dupont

In almost any commercial studio and many high-end home studios, you’ll find one or more Pultec EQs. What’s more, most software developers who create models of vintage processors have a Pultec plug-in or two on the market. Pultecs were initially manufactured in the 1950s by Pulse Techniques. (The “Pul” is from “Pulse” and the “tec” from “Techniques”).

Although the original company went out of business in 1981, it’s been resuscitated under new ownership and now makes accurate hardware versions of their venerable EQs. What’s more, quite a few manufacturers make “clone versions” of Pultecs, including Tube Tech, Klark Teknik and Warm Audio, to name a few.

In this excerpt from How to Listen—Pultec Edition, Fab demonstrates a technique for setting a Pultec’s Low-Frequency band that might strike you at first as counterintuitive but is actually extremely useful. We pick up the action with Fab in the studio with a silver-faced Pultec EQH-2 unit.

The EQH-2, which is a mono unit like most other hardware Pultecs, was first built as a smaller-sized (2RU) alternative to the (3RU) EQP-1. It has only two bands (a low shelf and a high peak) as compared to three in the EQP-1A (low shelf, high peak, high shelf) but has the same filter shapes for the low band, so as far as the technique Fab demonstrates in this excerpt, they’re interchangeable. Pultec also made an EQ focused on the midrange called the MEQ-5, which Fab also has in his studio, and is visible in the excerpt.

From Fab’s studio, a Pultec MEQ-5 (top) and an EQH-2 (bottom).

Pultec FAQ

Pulse Technologies designed Pultec EQs with inductor-based circuitry (inductors are a type of component), which produces a bit of saturation, making them very musical sounding. The filters in Pultecs are of the passive variety, which creates a level loss in signals that pass through them.

To compensate, Pulse Technique included a gain stage after the filters. In many Pultec models, these were tube-based, which added additional sweetness to the tone. As Fab shows in the full video (available to Puremix Pro members), just putting a source through a tube Pultec without any boosts or cuts, usually improves its sound.

The frequency bands in Pultecs are not continuously variable. Instead, they each offer a small number of preset frequency selections. For example, the low band on the EQP-1a and the EQH-2 has only four frequency options: 20Hz, 30Hz, 60Hz and 100Hz for the low band. While having so few bands may seem limiting, they’re well-chosen and have wide bandwidths that impact signal well above or below the selected frequency.

The low-band frequency choices on Pultec EQs (CPS stands for cycles per second. 1 CPS is equivalent to 1Hz).

For example, even if you set the low band for 30Hz, the shelf is so broad that it impacts up to the 1000Hz area. Likewise, the high band affects frequencies down to the lower midrange. On the EQP-1A, unlike the EQH-2, you can adjust the bandwidth of the upper peak band.

One of the advantages of the Pultec EQs and their clones is that they feature separate boost and attenuation knobs on the low bands. Unlike other EQ types, where you’d have a single knob that can either boost or cut, you can do both simultaneously on Pultecs, which is the technique that Fab demonstrates in this excerpt.

One Way and the Other

At first, the “2-knobs technique” seems counterintuitive, because you’re boosting and cutting the same frequency simultaneously. Logically you’d think that one would offset the other. Even Pulse Techniques thought that in the beginning, and warned against it in the manual.

But as it turns out, you can create unique settings by using both together. Engineers discovered that the Boost and Cut parameters don’t have the exact same frequencies or filter shape. As a result, rather than one knob offsetting the other, combining the two allows you to achieve settings that would be impossible with one knob. For example, as Fab demonstrates, you can use the Attenuation to reduce some midrange muddiness that can occur when you boost the low band with its wide filters.

Using the Boost and Attenuate knobs together can create settings you can’t get with either alone.

Show It

Fab demonstrates the technique using a stereo drum loop. Because the EQH-2 is mono, he sums the output to a mono channel where he places the EQH-2 as a hardware insert in Pro Tools.

He turns on the drum loop with the low band of the EQH-2 set to 60Hz and the high band off. He applies a moderate boost to start but then says, “What if I wanted more?” and boosts it up over five. Now it sounds thick, but a little muddy. So he brings the Attenuation into the circuit, raising the knob to just under three. The sound thins out some, but the drums still sound much beefier due to the boost.

Fab points out that while you might think you could get the same effect by just turning the boost knob lower, you can’t. To demonstrate, he removes the Attenuation and reduces the Boost to a little over 4. He observes that he can’t get the same amount of peak at 60Hz as he did using the two knobs together. That’s because the shape of the filter changes with the Attenuation turned on, cutting more of the lower midrange.

He then opens the iZotope Insight 2 plug-in in its spectrum analyzer mode. He generates white noise with a tone generator and sends it through the Pultec so you can really see the impact of the knobs on the frequency response.

He compares the effect of boosting the bass, with and without attenuation. Without, the midrange frequencies are louder. Attenuating the signal brings it down overall between about 300Hz and 4KHz.

Fun with Pultecs

You can find plenty of uses for Pultecs, and there are many excellent plug-in versions. In the following examples, we’ll listen to the UAD Pultec EQP-1 on a couple of different sources, using the 2-knob technique.

In the first example, you’ll hear a section of a simple multitrack drum mix consisting of kick, snare, and stereo overheads.

EX. 1a: Here, the Pultec is bypassed.

EX. 1b: This time, the kick and snare tracks each have an instance of the EQP-1A plug-in inserted on them. The kick is boosted at 60Hz and the snare at 100Hz. Both are also boosted in the high peaking band.

EX. 1c: This time, the same boosts are in place, but, on each plug-in, the attenuation is modifying their effect. (See screenshot below). After you listen to this one, quickly go back and listen to EX 1a, so you can get the full impact of the setting compared to when the Pultec is bypassed.

The settings on the Boost knob are the same for Examples 1b and 1c, but the Attenuation is only used in Example 1c.

The second set of examples focuses on using the EQP-1a plug-in on electric bass. You’ll hear the bass in the context of a four-measure section of a multitrack mix session.

EX. 2a: There’s no Pultec on the bass. EX. 2b: The plug-in’s low-band Boost knob is set to about four at 100Hz, and the high peaking band is boosted at 3KHz. The result is a bit bass-heavy.

EX. 2c: With the same Boost settings as in Example 2b, the Attenuation knob is set at a little over four, reducing the bossiness a bit. It’s subtle, but if you focus on the bass when you listen, you’ll hear the differences.

The setting on Example 2c.