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## audacity-nyquist

 [Audacity-nyquist] Higher-order filters cannot use a signal for the cutoff frequency From: David R. Sky - 2009-08-21 06:30:43 ```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/ ```
 Re: [Audacity-nyquist] Higher-order filters cannot use a signal for the cutoff frequency From: paul beach - 2009-08-21 13:02:46 ```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" 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/ > > > ------------------------------------------------------------------------------ > Let Crystal Reports handle the reporting - Free Crystal Reports 2008 > 30-Day > trial. Simplify your report design, integration and deployment - and > focus on > what you do best, core application coding. Discover what's new with > Crystal Reports now. http://p.sf.net/sfu/bobj-july > _______________________________________________ > Audacity-nyquist mailing list > Audacity-nyquist@... > https://lists.sourceforge.net/lists/listinfo/audacity-nyquist -- paul beach sniffyraven@... ```
 Re: [Audacity-nyquist] Higher-order filters cannot use a signal for the cutoff frequency From: Roger Dannenberg - 2009-08-24 18:54:31 ```Hi David, It looks like the higher-order filter functions cannot be modulated with signals. I can put this on my list of things to extend in the future. The reason for using higher-order filters instead of a cascade of lower-order filters is that you can make filters better-behaved, e.g. a flatter frequency response in the pass-band, by optimizing the filter coefficients. For now, I guess you are stuck with the cascade approach. -Roger ```
 Re: [Audacity-nyquist] Higher-order filters cannot use a signal for the cutoff frequency From: David R. Sky - 2009-08-24 20:29:06 ```Thanks Roger, Paul had responded about using the reson filter, which I'd used years ago but forgotten about - it works much better than what I had been looking for. :-) David -- David R. Sky http://www.shellworld.net/~davidsky/ On Mon, 24 Aug 2009, Roger Dannenberg wrote: > Hi David, > It looks like the higher-order filter functions cannot be modulated with > signals. I can put this on my list of things to extend in the future. The > reason for using higher-order filters instead of a cascade of lower-order > filters is that you can make filters better-behaved, e.g. a flatter frequency > response in the pass-band, by optimizing the filter coefficients. For now, I > guess you are stuck with the cascade approach. > > -Roger > > > ```
 [Audacity-nyquist] Convert MP3 to wave/midi From: paul beach - 2009-08-28 06:10:09 ```Does Audacity have to record midi files in real time? My wave file has clicks. MP3 phrase of Hildegard of Bingen(1098-1179) http://www.climatehoax.ca/image/hildegard.mp3 -- paul beach sniffyraven@... ```