Peak filter first order?


is there any Peak Filter first order (6db/oct) available out of the box in JUCE?

I’m following this tutorial JUCE: Tutorial: Introduction to DSP for Ladder Filter, but can’t find a “simple” first order Peak.

Any tips?
Thanks :slight_smile:

If I understand what you mean by a “peak” filter (a resonant filter), due to the laws of physics, a first-order resonant filter does not exist.

In Juce, there are other filter classes besides the Ladder filter, it’s just that the way they organized it, the Ladder filter is the only filter in the “dsp widgets” group. Take a look here for a bunch of other filter options, many of which can be made resonant:

I mean something like this: peak filter - Google Search

Biquad by RBJ for example have a Peak implementation, but they are second order by nature (i.e. bi-quad).

Hi Derozer!
Like refusesoftware said, a peak filter cannot be implemented as a first order filter.
It may help to view a peak filter like adding a bandpass. A bandpass filter needs to be second order or higher.
However, you may be able to combine two first order filters to produce a peak filter. Afaik there also are filter design approaches which are entirely based on combining multiple allpass filters.

dB/octave doesn’t really make sense for a peak filter since they have a bell shape - dB/octave is usually used to measure the steepness of a filter such as a low-pass or high-pass.

You can change the “steepness” of a peak filter by changing the Q - although this is seen more as widening the filter.

Could you maybe explain in more detail what you’re hoping to achieve and why the filters provided by JUCE aren’r sufficient?

I see, thanks.

For what I see on JUCE there are “only” the Peak of IIR type, using Transposed Direct Form II, correct?

Its a suite that I know really well, and just asking if there are some other sort of Peak filter out of the box to try it quickly and see how they sound :slight_smile:

Can you confirm this?
Maybe I’m looking at wring section…


Fun fact: the slopes of a 2nd order peak filter approach 6dB/oct outside of the peak region. Most of the time it’s “buried” in the 0dB line so it’s often not that obvious.

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@jcomusic: not sure about what you are suggesting here. Can I create a Peak filter starting from a Bandpass filter? Not sure “how”: isn’t the bandpass narrow only on the band, and the rest “going to -inf”. Peak filter is a “pump” of some freq, really different so.

Can you help me to understand what you mean here precisely?


The line of thought is, if you add a bandpassed signal to the original signal, you’ll end up with a boost at the bandpass frequency. That only works properly if the phase responses allow it. You can also think of a bandpass as a combination of high and low pass filters, which afaik is a valid approach to construct them. I’m no filter design pro though and not that deep in the topic at the moment, just wanted to leave some hints for diving deeper into the topic. Sorry for being not that helpful.

About the allpass stuff: It’s something I recently stumbled over when browsing through various filter design papers. I haven’t really dived into it, nor do I remember what exactly it was (I’ll let you know once I find it). But iirc the idea is that if you mix an allpass filtered version of a signal with the original, you’ll affect the magnitude spectrum of the output, and by constructing and combining allpasses in particular ways you can create all sorts of stuff based on one simple building block. But this is really from the back of my head and deep down in my “investigate this at some point” :wink:

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Another funny thing is this (just noticed on a VST plugin):


It seems a Band pass filter of the first order? I would say “6” means 6db/oct…

This is the SPAN response feeding an Impulse:

A “Band-pass 6” could be a first-order highpass in series with a first-order lowpass, both given the same cutoff frequency. Just because some VST plugin labeled a setting that way, it doesn’t mean that first order filters can be resonant.

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