Nova-67P and parallel equalizers explained

How do parallel equalizers work? The signal is passed through band-pass filters, gain applied and then the result is summed with the dry signal.

simple parallel equalizer

band-pass + dry signal = bell shape
low-pass + dry signal = low-shelf
high-pass + dry signal = high-shelf

What is so special about parallel equalizers in digital world? I like the way how bands interact with each other! Check the picture. There’s a typical serial equalizer on the left (SlickEQ GE). There’re 2 bands, 1 kHz and 2 kHz with +6 dB boost on both. In serial equalizers close bands tend to “stick” to each other and in parallel equalizers this effect is less prominent. The difference may be very subtle but for me a typical parallel equalizer provides greater bands separation especially in a busy midrange, which is very suitable for mixing tasks.

serial equalizer vs. parallel equalizer

Parallel equalizers and cuts. Most parallel equalizers operate in a very special way when combining boosts and cuts. Why? Just an example. If you boost an input signal of 1 Volt by +6 dB you have the resulting signal of 2 Volts. So a parallel equalizer adds 1 Volt to the output. If you cut -6 dB from an input signal you have the resulting signal of 0.5 Volts. Thus a parallel equalizer subtracts 0.5 Volts from the output. Now if boost and cut bands are close together a boost band always tends to win because it affects the output more than a cut band. In our example 1 V + 1 V – 0.5 V = 1.5 V (+3.5 dB of total boost). I don’t like such unpredictable behavior! The solution is to connect boost stage and cut stage in series. Check the picture. For this type of connection +6 dB boost and -6 dB cut compensate each other.

parallel equalizer with feedback path


Parallel equalizers and dynamic processing. Parallel equalizers are amazing for multiband dynamic processing because all necessary bands are already extracted from the signal! So it’s an easy trick to add multiband saturation or multiband compression here. Check the picture for the compression example. Now we have a parallel dynamic equalizer!

parallel dynamic equalizer

Each compression block returns gain reduction control signal (GR) to apply to the corresponding band. Is this dynamic EQ completed? No. We need external sidechain and it’s not bad to high-pass it!

parallel dynamic equalizer with external sidechain

Are we there yet? No. I want to control the gain of “dry” signal and to compress it too! Check the picture.

parallel dynamic equalizer with dry signal compression

Now we have split-band path where each band is compressed independently and we have new full-band signal path. “Anti-filter” is a composition filter inverse to band-pass filters (series of notch filters for example) and it is used to remove the portion of a control signal already processed by split-band path from our full-band compressor. “Compensation” is a special signal to compensate gain change for the dry signal, which affects bands too. With this compensation the full-band compressor and split-band compressors don’t affect each other.

And in [Nova-67P] there’s also “emphasis” filter inside “Anti-filter” block. It allows full-band compressor to be more sensitive for some frequencies and less sensitive for another. Actually it’s one more parallel EQ hidden inside this block.

I hope this short and easy description helps you to understand [Nova-67P] plugin better.




12 responses to “Nova-67P and parallel equalizers explained

  1. Sam 2014/08/10 at 03:30


  2. Olli 2014/08/10 at 17:23

    Thanks for the explanation!

  3. Ezequiel Morfi 2014/08/18 at 08:11

    Awesome! Thank you VLADG for this great article.

    (Although I’m still not quite sure about the difference between a serial and a parallel EQ as far as the routing and the interaction of the bands go)

  4. Vyedmic 2014/09/13 at 13:59

    Amazing and super flexible! Where is the donate button? 😉

  5. Boz 2014/09/18 at 13:33

    Hey, I have some questions about the filter cut implementation. I’m following your block diagram, and it’s just not giving me the right results for cuts. Can I talk to you about what I might be missing?

    For example, let’s pretend I have 2 filters with 6dB cuts at the same frequency, If I do those in parallel, I get -0.5 + -0.5 which is negative infinity, as opposed to boosting where two filters of the same frequency just give me an extra 3.5 dB of boost (as it should).

    • vladgsound 2014/09/18 at 22:41

      Basic parallel EQ works in the following way: out = in + bandpass1 * (gain1 – 1) + bandpass2 * (gain2 – 1) + … So if you have equal bandpasses and gain1 = 2 (+6 dB) and gain2 = 0.5 (-6 dB) you have: out = in + bandpass * (2 – 1 + 0.5 – 1) = in + bandpass * 0.5 = in + bandpass * (1.5 – 1) or 3.5 dB boost (1.5 = 3.5 dB). So you’re right about 3.5 dB here. I don’t understand what did you miss?

      • Boz 2014/09/19 at 21:54

        I’m mostly lost with the cut section. The boost section works exactly as I would expect. Let’s say you have 2 cuts, both of the -6dB at the same frequency. that would give us:

        out = in + bp1 * (gain – 1) + bp2 * (gain – 1)
        out = in + bp1 * (0.5 – 1) + bp2 * (0.5 -1)
        out = in + bp1 * (-0.5) + bp2 * (-0.5)
        out = in – bp1*0.5 – bp2*0.5

        Since bp1 and bp2 are the same in this example

        out = in – bp

        So at f0, I end up with a notch filter.

        Ideally, having two cuts of -6dB at the same freq should give us a total of -9.5dB (opposite of what you get with two boost filters in parallel).

        I’m clearly missing something in the cut section.

  6. Aleksashka Zilkov 2014/12/02 at 16:34

    you’ve lost me on the 3rd step, but i feel it in my guts that you are a wonderful person!))

  7. Nekro Dean Frogzwell 2015/02/11 at 19:45

    Great article my friend as always, Parallel equalization offer so much power whilst also being very unobtrusive if needed I find. Cheers

  8. Frank 2019/09/09 at 15:50

    This is a really great explanation of parallel EQ – thank you. The equation: out = in + bp1 * (gain1 – 1) + bp2 * (gain2 – 1) + … does not seem to work for the cut section. Is the equation for the cut section different?

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