Hi David,
Only two filters accept a signal, low pass and resonant. All filters
accept a flownum which is not a signal. For the plug-in below, you can
switch lp to reson.
Nested lp and reson filters work. In the complex plane it is anologuous
being squared. It is rather tricky mathematically, though it may be
something that you can hear.
There was also a question about alias. A stereo MP3 that is compressed
too much will alias, that is high frequency compenents are mixed down to
the sensitive part of hearing, and clearly, be very tiresome.
;nyquist plug-in
;version 1
;type generate
;name "Guitar_1..."
;action "Generating sounds..."
;control p "Pitch" real "Frequency" 60 10 100
;control t "duration" real "Seconds" 1.5 0.5 10
(setf f ( step-to-hz p ) )
(stretch t
(lp
(sim
(osc-tri (* f 1) )
(scale .5 (osc-tri ( * f 2)))
(scale .75 (osc-tri (* f 3)))
(scale .25 (osc-tri (* f 4)))
(scale .125 (osc-tri (* f 5)))
)
(mult (exp-dec 0 (+ .1 ( / 15.0 f )) 1 ) f )
)
)
On Thu, 20 Aug 2009 23:30:26 -0700 (PDT), "David R. Sky"
<
[hidden email]> said:
> Hi,
>
> A few weeks back Paul posted a question about higher-order filters such
> as
> lowpass2 etc. not being able to do filtering when the cutoff frequency is
> a signal such as an LFO - I showed how to do this with nested or layered
> lp filters. But Roger's response seemed to indicate that higher-order
> filters _should_ be able to do this in Audacity - at least the latest
> version 1.3.8 beta with the newer Nyquist functions. (Sorry if I
> misinterpreted your response Roger.)
>
> I just tried this with lowpass2, as it has the optional resonant q
> argument, which I want to implement in a plug I started working on.
>
> And I had the same problem as Paul - using a signal to change the cutoff
> freq only works with the lowest-order lp function in Audacity 1.3.8 -
> despite even making sure the LFO signal I was using for filtering was
> above the zero line, which the lp filter accepted without complaint (and
> it even accepts a signal which _does_ cross the zero line).
>
> Is there a way I can solve this? - even adding something to an lp defun
> so
> that I get the resonant quality? Without fakery such as adding an
> fm-induced signal...
>
> Thanks
>
> David
>
> --
> David R. Sky
>
http://www.shellworld.net/~davidsky/>
>
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