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SD-PE1: Passive Power, Classic Character

Slate Digital is thrilled to introduce SD-PE1, our brand-new passive EQ plugin.

A welcome addition to the Virtual Mix Rack ecosystem, SD-PE1 is based on one of the most coveted and beloved passive EQ units ever made. SD-PE1 delivers all the signature tone and color that made the original hardware unit so beloved, with some extra features sprinkled to make it even more useful.

At a Glance:

  • Passive EQ plugin
  • Digitally modeled off legendary outboard unit 
  • Additional frequencies for deeper processing 
  • Stepped and incremental frequency selection 
  • Toggle traditional tube-stage saturation on/off 
  • Perfect for drums, bass, vocals, and mix bus 

The original passive EQ that inspired SD-PE1 first appeared in the late 1950s. Immediately beloved for their notably warm quality, the earliest units were all made by hand by the company’s founders. This strict attention to detail resulted in superior build quality that has led to many of these original units still working more than 60 years later. 

Built-In Vintage Warmth

Top-third view of SD-PE1 passive EQ plugin GUI showcasing the Tube Stage on/off switch.

On passive EQ units, the processed signal is output at a significantly lower volume than the input signal, requiring an additional clean boost step to hear the results of the processing. To remedy this issue, the original hardware also featured a built-in tube makeup gain stage that boosted the outgoing signal back to the desired level while adding an extra dose of saturation to it.

SD-PE1 captures all the iconic richness and tone of the original unit—with a twist. The plugin features the same tube stage, but as a switch that can be toggled on and off. This feature allows you to keep your crafted EQ curve without any additional coloration from the tube stage.

Unique EQ Curves

The original unit gained fame for its distinctive low-end boost and attenuation capabilities, especially in the sub and low-mid frequencies. Its renowned “kick trick” simultaneously boosts and attenuates the same frequency, creating a unique resonance that enhances clarity and depth without compromising warmth or punch.

This feature has established the EQ as a must-have in mastering studios, where it enhances recordings with weight and presence while preserving a natural, transparent sound. Ultimately, the SD-PE1’s EQ curves deliver a timeless and unmatched sonic character, cementing its status as the best passive equalizer plugin for achieving professional-grade audio results.

Further Frequency Selection

Middle-third angled view of the SD-PE1 passive EQ plugin GUI showcasing frequency selection knobs.

SD-PE1 also adds several additional frequencies that the original unit didn’t allow for. The high shelf control can now reach 3kHz on the low end and 30kHz on the high end. The high bell can now boost 1kHz and 2Khz, and the low shelf can affect 40Hz and 70Hz. These extra frequencies further enhance the sonic flexibility of the plugin without sacrificing the experience of using the original module. 

To take things a step further, where the original hardware’s frequency selection was stepped, SD-PE1 allows for both stepped and incremental frequency selection. This means you can use the plugin both exactly as the original hardware was intended and as your own unique custom passive EQ.  

Making the Plugin

In the video below, hear from our DSP team about how they built SD-PE1 and translated all the essential nuances of the original unit into this new plugin.


SD-PE1 is available NOW in Virtual Mix Rack for All Access Pass and Complete Access subscribers. It is also available for purchase at $149 as a perpetual license. Learn more and try it today here.