[sdiy] Filter slopes

[Scott Gravenhorst]

Also, a friend of mine, Les Hall on electro-music.com, came up with an analog way to do
Karplus-Strong using a BBD and a single pole low pass analog filter (just RC) in the loop. 
This works and might also be applicable to the flute model described on ccrma.standford.com. 
That might be tricky to get working, but probably not impossible.  If I were to try it (I'm not
really an analog guy now), I'd start with Les Hall's BBD KS circuit and see what the problems
are with it.  Another friend implemented it (BBD KS) and he said it suffers the same problem
that the digital model has - the low pass filter adds a bit of extra delay so it detunes a bit
as the delay is shortened.  Delay time is controlled by using a VCO as a clock to drive the BBD.

music.maker at gte.net wrote:
>
>
>Look at Perry Cook's flute model:
>
>https://ccrma.stanford.edu/software/clm/compmus/clm-tutorials/pm.html#s-f
>
>It's an extension of Karplus-Strong string models. There are two 
>delay lines, one is exactly 1/2 the length of the other. The 
>short one models the mouthpiece and it energizes the long one. 
>I've gotten it to work and it sounds VERY flute-like, however, I 
>still need to work on it because it comes to full amplitude very 
>slowly with whatever mistake I made. I'm sure another look at my 
>code and I'll see a doofus thing I did. 
>
>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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>>> 
>>> 
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>
>-- ScottG
>________________________________________________________________________
>-- Scott Gravenhorst
>-- http://scott.joviansynth.com/
>-- When the going gets tough, the tough use the command line.
>-- Matt 21:22
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-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- http://scott.joviansynth.com/
-- When the going gets tough, the tough use the command line.
-- Matt 21:22