[sdiy] Filter slopes

[Ian Fritz]

Well, suppose you have a set of filters in parallel. One way of coupling them would be to add a small amount of Output A to Input B, etc.  Don’t recall this being done in an analog synth context.  I think this would work best if there were nonlinearities in the filter response, though.  Linear coupling might be a weak effect.  Just some thoughts, haven’t tried anything like this.

Ian



> On Jun 11, 2018, at 4:28 PM, Adam Inglis <21pointy at tpg.com.au> wrote:
> 
> Yes, the term “coupled resonators” had me intrigued as well - sounds like a potentially powerful mechanism… Achim?
> 
>> On 12 Jun 2018, at 8:04 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
>> 
>> Ok, I don’t know anything about “coupled resonators”. What would I look up to find out more (aside from that obvious term ), and how would I implement such a thing for analogue audio? Making “resonators” is easy enough. How do I “couple” them?
>> 
>> I’m looking for a practical implementation with details of how that was arrived at, rather than a highly abstract splurge of math that I won't understand and which could probably be explained in words of two syllables or less if anyone took the time to bother.
>> 
>> Thanks,
>> Tom
>> 
>> ==================
>>      Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
>>> On 11 Jun 2018, at 20:50, ASSI <Stromeko at nexgo.de> wrote:
>>> 
>>> On Monday, June 11, 2018 7:43:22 AM CEST Elain Klopke wrote:
>>>> I was reading an article about the spectral content of various instruments
>>>> (woodwinds and strings) and while they didn't have any circuits, there were
>>>> some tables showing cutoff frequencies and high and low slopes. Several of
>>>> the pictures looked like bandpass filter responses with different slopes on
>>>> each side. How would I go about doing that? Is the slope determined by the
>>>> gain of the op amp in an active filter? If it's that easy, would it be a
>>>> highpass filter followed by a lowpass filter each with their own gain
>>>> settings?
>>> 
>>> Both woodwinds and string instruments (among others) can be modeled with 
>>> coupled resonators.  The characteristic timbre of each is related to the modes 
>>> of these resonators and the transfer of energy between them.  The slopes of 
>>> the bandpass skirts depend on both the quality factor of the resonator and the 
>>> coupling strength to other resonators or resonator modes.  Generally speaking, 
>>> losing energy (e.g. into another mode) is a reduction in Q and hence shows up 
>>> as a flattening of the slope.  If you just want to approximate the magnitude 
>>> response, a filter bank with a high enough number of filter bands is as good 
>>> as any other method and relatively easy to implement, it just uses many de-
>>> coupled resonators instead of few(er) coupled ones.
>>> 
>>> 
>>> Regards,
>>> Achim.
>>> -- 
>>> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
>>> 
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