In a project I am working on I am using a [bp~] to mimic a helmholtz resonator. The difficult part is that this cilinder I am modeling is constantly changing its volume, thereby changing its resonant frequency and Q.
This works well at lower speeds but the trouble is that the cycles go up to once every 30 milliseconds. This means that the frequency and Q go up and down again 33 times per second. Long before these frequencies this setup tends to explode and create feedback.
My thoughts about my problem tend to point at the Nyquist frequency of control signal sample time. Is this true and can I change the sampling speed of control signals? Of course I thought about sending the data in audio signal but [bp~] does not accept that of course.
Is there another filter out there that I can control with audio signals if I cannot change the control signal sample speed?
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Þurstan Skallagrimsson wrote:
Is there another filter out there that I can control with audio signals if I cannot change the control signal sample speed?
[block] can be used to control the blocksize, which affects the control rate. For controlling filters at audio rate, check out [vcf~] or better check out the iem filter abstractions, for example [lp2~] or any of the other filter abstractions using the [filter~] object. They should be in the iemlib or iemabs folder in CVS or in the extended installers.
That said, I've found that filters are not exactly PD's strong point. They tend to "blow up" much more easily that in other DSP programs I've used or seen (Reaktor, SuperCollider, etc).
Good luck, d.
On Tue, 2006-10-31 at 18:55 +0100, derek holzer wrote:
That said, I've found that filters are not exactly PD's strong point. They tend to "blow up" much more easily that in other DSP programs I've used or seen (Reaktor, SuperCollider, etc).
is that related to the 'system' pd, or is that just, because no 'good' filters have been implemented yet? i just want to add, that i never noticed that the filters in standard pd or from iemlib tend 'to blow up'. this might be, because i never seriously worked with reaktor nor supercollider and have no comparison... so i just wonder about the quality of the mentioned filters in pd.
btw: is [vcf~] the only known filter with a signal-frequency-inlet?
roman
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On Tue, 31 Oct 2006 23:33:23 +0100 Roman Haefeli reduzierer@yahoo.de wrote:
On Tue, 2006-10-31 at 18:55 +0100, derek holzer wrote:
That said, I've found that filters are not exactly PD's strong point. They tend to "blow up" much more easily that in other DSP programs I've used or seen (Reaktor, SuperCollider, etc).
is that related to the 'system' pd, or is that just, because no 'good' filters have been implemented yet? i just want to add, that i never noticed that the filters in standard pd or from iemlib tend 'to blow up'. this might be, because i never seriously worked with reaktor nor supercollider and have no comparison... so i just wonder about the quality of the mentioned filters in pd.
I've never noticed any instability in Pd standard filters either, and I've certainly punished them enough. The only time I've really seen the sharp end of Pd filters is messing with [biquad~] and [pole~] designing my own, but if you play with fire...
btw: is [vcf~] the only known filter with a signal-frequency-inlet?
Actually I forgot [moog~], which also allows a-rate Q control afair, which kinda answers the OPs question.
roman
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Roman Haefeli wrote:
btw: is [vcf~] the only known filter with a signal-frequency-inlet?
No, as I wrote there is also [filter~] and all the IEM abstractions that use it.
More details on my own PD filter issues forthcoming ;-)
d.
derek holzer ::: http://www.umatic.nl ---Oblique Strategy # 91: "Infinitesimal gradations"
Yes, convert your control signals to audio rate with [sig~] (maybe interpolate them too using [line~]) and then use [vcf~] which has an audio rate Cf
I'm not sure about a-rate control od Q though.
On Tue, 31 Oct 2006 17:22:47 +0000 "Þurstan Skallagrimsson" thurstan666@hotmail.com wrote:
In a project I am working on I am using a [bp~] to mimic a helmholtz resonator. The difficult part is that this cilinder I am modeling is constantly changing its volume, thereby changing its resonant frequency and Q.
This works well at lower speeds but the trouble is that the cycles go up to once every 30 milliseconds. This means that the frequency and Q go up and down again 33 times per second. Long before these frequencies this setup tends to explode and create feedback.
My thoughts about my problem tend to point at the Nyquist frequency of control signal sample time. Is this true and can I change the sampling speed of control signals? Of course I thought about sending the data in audio signal but [bp~] does not accept that of course.
Is there another filter out there that I can control with audio signals if I cannot change the control signal sample speed?
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derek holzer -
padawan12 -
Roman Haefeli -
Þurstan Skallagrimsson