Hi Everyone,

I'm trying to recreate all the filter types in Logic's ES2 synthesizer:

So essentially, I want to build:

Filter 1:

• a resonant lowpass
• resonant highpass
• 'peak' filter
• band reject filter
• band pass filter

Filter 2:

• 12 dB resonant lowpass
• 18 dB resonant lowpass
• 24 dB resonant lowpass

with an optional "fat" setting that restores low frequencies when the resonance is turned up.

I'm very much a noob when it comes to low-level filter design. Is there any good tutorials/documents/places to start for a project like this?

Thanks,

-chmod

This is a great resource on lots of DSP related topics: https://ccrma.stanford.edu/~jos/filters/

Thanks! Reading that now.

So I took a look at that page, and I don't have any experience with the type of math that is involved. Would anybody be able to give me a list of what mathematics topics I should study as a prerequisite for reading this document?

Any suggestions would be greatly appreciated!

Hey chmod, I just did a relatively quick test of the ES2 filters by running white noise through them and observing the frequency response. As it happens, Filter 1 is a state-variable filter, which is already implemented as [cyclone/svf~], so the work is already done there. They're pretty much exactly the same. I believe the Peak filter mode is just the sum of the band-pass output and the original signal.

Filter 2 is a bit more complicated. Since it can self-oscillate, it means there is some sort of non-linear function in feedback part of the filter. These types of filters are impractical to design in Pd alone and are best done as externals. The closest external I know of to this is [muug~], which saturno uploaded to this thread. It seems to be at -24 dB roll-off, which isn't adjustable.

For the Fat setting, it looks like the filter brings down the output level a bit when raising the resonance. The compensation simply comes by just increasing the input level when the Fat switch is on.

Hope that helps.

Thanks Maelstorm! I've decided to use svf~ for both filters, that way the user gets a bit more of a variety for both stages. The synth that I'm making isn't strictly an ES 2 clone either, so the svf~ object is exactly what I needed!

Thanks again!

Another question about the ES2 in case anyone is interested:

With the ES2 you are able to modulate the frequency of osc 1 with the output of osc 2, and you are also able to ring modulate osc 2 with the output of osc 1 (in the Logic documentation, it is explained like this: "The Oscillator 2 ring modulator is fed with the output signal of Oscillator 1 and a square wave—generated by Oscillator 2 itself.").

What should I expect when I have both the ring modulation and the fm modulation on at the same time? In the ES 2 it produces an undulating, rich harmonic tone, but my patch in the same configuration produces not-so-harsh noise. It seems like noise would be the obvious result of a signal being modulated by another signal being modulated by the original signal (confused yet?)... does anyone know what's going on here?

Thanks