How would you configure and use [bob~] to demonstrate what the ladder filter fuss is all about? For some reason (inexperience? poor taste?) I keep returning to [vcf~].

Edit: after an hour or two of monkeys at the typewriter, I'd say that the 2 main differences from [vcf~] are the roll-off slope ([bob~] never completely mutes signal even when the cutoff freq is 8 hz) and the resonance sounds brighter and grittier (bob at resonance 3 sounds like vcf at q 22 to me). There's got to be more to it than that, right?

@jameslo [bob~] is not very good, I would never guess it was a transistor ladder if it did not say so, never would guess it was an emulation of an analog VCF even. 90% of the transistor ladder sound is it being 4-pole, the moog sound is just as much the VCOs with their rather bent waveforms. A few of the early ARP synths used a transistor ladder which is ultimately just a slight improvement on the early moog ladder and almost identical to the later moog ladders, but no one every mistakes those ARPs for moogs and they sound nothing alike. Four [vcf~]s in series will probably get you closer to the ladder sound than [bob~], [vcf~] is a pretty good lowpass.

I wonder if you can do pole mixing in pd...

I wonder if you can do pole mixing in pd...

Pole mixing in itself should be trivial -see: https://electricdruid.net/multimode-filters-part-2-pole-mixing-filters/ and my crude implementation:

(You could replace [lop~] with [vcf~])

The problem is implementing proper feedback/resonance. See this digital implentati0n of the moog ladder (from https://www.researchgate.net/publication/241280072_POWERWAVE_-A_HIGH_PERFORMANCE_SINGLE_CHIP_INTERPOLATING_WAVETABLE_SYNTHESIZER ):

The single RC stages would be easy to to replicate but to get proper (0 latency) feedback you'd have to stuff everything into a single [fexpr~] object (or design it with a block size of 1?).

Something for @jameslo to tinker with

@oid I was afraid to reach that conclusion, but you make a strong case. I wonder if [audiolab/pp.ladder~] is closer?

@bocanegra He he he....

@jameslo @oid there's also [ggee/moog~] and [muug~] https://github.com/pcasaes/muug
I often use [cyclone/svf~]'s lowpass. not sure why [bob~] sounds so unlike a lowpass.. maybe miller overlooked something, or maybe it's not as steep as other lowpasses.. Personally I still like the sound of it tho. (although it's more like a peaking/lowpass hybrid)

This is the automatonism implementation of the bob~ object. This module sounds really nice moogish

@tungee Thanks. What's going on with the rightmost [bob~] instance? Should it's attenuated output be connected to the outlet?

And here the Ladder mod of automatonism

In my opinion the power of the Bob object is leashed, when more then 1 Osc is feeded into the Bobcat like in a real analog synth( 2 OSc+ plus subosc)

@jameslo I think the output of the 0.33~must be routed also into the output

As the feedback/resonance problem has been solved in @oid 's polemixing thread, here is a simple yet somewhat CPU expensive implentation of the moog ladder with signal rate cut-off inlet (without sigmoids in the filterloops tho): 4stageLadder.pd

There is an output for each stage so you can do your pole mixing should you want to, but for pure googelymoogely sound just use the last output

Inlets: Signal, Cut-off, Resonance

Hi Bocanegra what are ranges of the cutoff frequency and resonance? Bytheway thank you. Nice and compact solution

@tungee cutoff clips at around 14KHz i think (samplerate/2pi) - I haven't tried out frequency above 10k. Resonance is theoretically infinite, but I haven't gone beyond 15 in my test. Above 3 you will begin to hear some distortion of the feedback signal.

I also started a thread here, asking for help for optimising a Karlsen Ladder filter. I think we ended up with a decent optimised low pass filter. The high pass is not good, it could be a lot better. But I like the sound of the low pass filter.

https://forum.pdpatchrepo.info/topic/13202/looking-for-help-for-optimisation-of-karlsen-24-db-ladder-filter/29

It has oversampling implemented too.

@ bocanegra
i used 20hz to 14000hz for the cf and 0-15 for the resonance... but the resonance affects the sound very subtle. Is it so wanted?

@jaffasplaffa
i do like the karlsen Lp very much

@tungee - my mistake. I just took the guts from my version of @oid 's polemix which I had been doing all my testing on and thus forgot to invert the feedback.

Fixed version: 4stageLadder.pd

Basically just made the averaging filter in the feedback loop invert the signal. Weird because there is no inversion of the feedback signal in oid's polemix

I tested it again bocanegro, but the resonance is far from selfresonance. I miss the aggresiveness of the resonance somewhat

Bildschirmfoto 2021-09-07 um 21.26.51.png

test4stageladd.pd.zip

@tungee - the feedback chain has a softclipper (tanh function) that makes it overdrive at >3 resonance but never hit the 1/-1 clipping wall. Try cranking it up to 25 and see. Or open it up and bypass the [expr~ tanh($v1/5)] object in the feedback path - but then your should be careful with resonance values > 1...

@tungee Judging from your screenshot you still haven't inverted the feedback path. Do like this:

@bocanegra said:

Weird because there is no inversion of the feedback signal in oid's polemix

Sure there is, look harder, I multiply the resonance paths mix ratio's by -1 when the filter mode/resonance path combination requires inversion . Part of the trick which keeps the resonance morph from sounding blah.

@oid - you are right! I have been starring myself blind at the lower left of the circuitry and missed out on all the mixing trix