Hi ! Thanks a lot for all your replies. Yes it helps a lot to get started on the right track. It also gives me good direction to dig to improve the basic results and achieve a "personal sound design" (something different than the ready-made filters that I have). At least to try something with low level building blocks.
> But it is having the resonance in parralel to a dry sound that bothers me; but may be that's the only way to do ? >>> > I'm not sure what you mean but I think you need some study in filter design Sorry about that : I was refering to a lowpass+bandpass in parallel, but only the band pass would resonate. But in fact I know the result sounds like two parralel filters :-) and is not the right way to do it. Thanks. Mehdi 2018-07-21 4:33 GMT+02:00 Andrew Simper <a...@cytomic.com>: > Resonance is just delay with feedback. Resonance occurs when you delay a > signal and then feed it back with some gain to the input of the delay "in > phase" with the original input, which means the delayed signal adds > together and boosts the input level to the delay. If you use a normal > digital delay line you get what is called a linear phase delay, so each > frequency is delayed by the same amount. If you use an IIR filter to delay > the signal you get what is called a non-linear phase delay, so each > frequency is delayed by a different amount. The particular arrangement of > multiple stages of delays and how the feedback is arranged both around > individual stages and globally all determine the structure of the filter, > and the type of filtering achieved. > > Most synth filters use IIR filters. The amount of non-linear phase delay > is typically referred to in terms of degrees, as this is usually more > useful for filter design. When the signal has been delayed 360 degrees at a > particular frequency, if you add this to the input signal you get a boost > in amplitude of that frequency since it is back in phase with the input, > which is called constructive interference. With enough feedback gain a > resonant peak will form as the constructive interference is in a feedback > loop with itself. Most resonant filter designs use the fact that taking the > negative of a signal actually changes the phase by 180 degrees at all > frequencies. So most filters delay the phase of the signal by 180 degrees > somehow, then subtract this from the input with some gain (negative > feedback) and so form a resonant peak. > > Many people have spent a lot of time forming many types of low pass > resonant filter structures. In synths it is mostly the non-linear > properties that very between different filters, there are actually only 3 > structures typically used to form low pass resonant filters: multiple IIR > one pole integrators with feedback (svf) or multiple IIR one pole low pass > filters with feedback (sallen key, cascade). > > Andy > > > On Sat, 21 Jul 2018 at 01:29, Spencer Jackson <ssjackso...@gmail.com> > wrote: > >> Resonance is the characteristic of some systems to store and release >> energy at particular frequencies. It's not limited to filters, mechanical >> systems like springs or pendulums have resonance (get on a swing at the >> park and try to change your frequency and you'll feel the effects of >> resonance). >> >> In an electrical system, a minimal passive resonant circuit would be one >> with 2 capacitors and 2 resistors. Selecting the values of the components >> determines the frequency, but what happens is that at a certain frequency >> the energy gets stored and passed back and forth between the capacitors, >> like the swing going back and forth. This storage and energy swapping >> emphasizes that frequency. Depending on the "Quality factor" or amount of >> resonance that frequency can become much more apparent than the other >> frequencies in the signal even if the input is wide-band. >> >> When you are talking about delay and feedback, you are creating a digital >> filter, but I think it is worthwhile to spend some time understanding the >> theoretical concept and think in terms of energy and frequency. Your >> feedback delay becomes the storage and certain frequencies will resonate >> with that system. >> >> > But it is having the resonance in parralel to a dry sound that bothers >> me; but may be that's the only way to do ? >> >> I'm not sure what you mean but I think you need some study in filter >> design, because a single feedback delay causes comb filtering but its not a >> classical lowpass. Is that what you are trying to achieve? Digital filters >> are almost universally combinations of short delays (typically 1 sample) >> placed in different patterns and fed back in different amounts (e.g. >> https://en.wikipedia.org/wiki/Digital_filter#Filter_realization). >> >> Here are some resources that may help you: >> http://www.dspguide.com/ch14.htm >> https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/ >> VAFilterDesign_2.0.0a.pdf >> >> That first one is a book that can help you more with the fundamentals in >> the early chapters as well. I hope this is somewhat helpful, if not perhaps >> I need to understand better specifically what you are trying to achieve. >> _Spencer >> >> >> On Fri, Jul 20, 2018 at 10:13 AM, Mehdi Touzani <mehdi.touz...@gmail.com> >> wrote: >> >>> Hi all, >>> I follow the llist for a while, but I am not a DSP programmer, I do DSP >>> audio apps for about 20 years now, for sonic core plateform "Scope" and >>> Xite". I begin with other things like juce or flowstone, but so far, >>> scope is still far superior in terms of sound results. Too bad there is no >>> scripting tool for it (well there is but it is not available to me). >>> >>> My question is probably weird for you - like super noob - , because i >>> am NOT looking for math or codes, but hints about a general >>> design/architecture. >>> >>> So... how do you do a resonance in a lowpass circuit? :-) not the >>> math, not the code, just the architecture. >>> >>> Personnally, i came to the conslusion that some kind of very short >>> delay with feedback, mixed in parallel with the non resonance low pass >>> sound, could do the trick. . The more feedback, the more resonance, and >>> with feedback over -6dB, it would begin to self resonate. >>> >>> But it is having the resonance in parralel to a dry sound that bothers >>> me; but may be that's the only way to do ? >>> >>> I have read about hardware filters and ok, there is math, but there is >>> also the effect of the hardware components. Some articles even suggest that >>> a bandpass in parralel could do the trick : or more exactly, a bandpass >>> fonction is created after the resonance, to remove frequencies that would >>> overlap with the cutoff. >>> >>> >>> So, any hints that could help me improve the process etc would be very >>> welcome. >>> >>> Thanks >>> >>> Mehdi >>> >>> _______________________________________________ >>> dupswapdrop: music-dsp mailing list >>> music-dsp@music.columbia.edu >>> https://lists.columbia.edu/mailman/listinfo/music-dsp >>> >> >> _______________________________________________ >> dupswapdrop: music-dsp mailing list >> music-dsp@music.columbia.edu >> https://lists.columbia.edu/mailman/listinfo/music-dsp > > > _______________________________________________ > dupswapdrop: music-dsp mailing list > music-dsp@music.columbia.edu > https://lists.columbia.edu/mailman/listinfo/music-dsp >
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