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Variable low pass filtering?

Standard audio low pass filters tend to work by adjusting the corner instead of the roll off or in some sense a one sided Q. So your standard treble control is a simple RC low pass filter with R being a pot. We have been conditioned by years of use to understand how these filters work but they are not the only ones.

What about changing the roll off rate instead or as a combination with the corner? Something that shifts the corner and increases the roll off? I suppose this is hard to realize in hardware because it requires a way to vary between a large number of poles smoothly? At least in the analog domain.

I wonder what such filters would look like and sound like?

Reply to
Bobby Joe
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On Aug 9, 11:48=A0am, Bobby Joe

I guess you can simulate such filters with a DSP, and listen to the audio result while playing with the parameters.

Reply to
Jean-Christophe

A standard PC should do it, too, if you don't want to do it for 6 channels and 96 kHz in parallel and you don't care about some 100 ms latency.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de
Reply to
Frank Buss

Yeah, it's not hard to implement digitally. Take the fourier transform, Multiply by the transform and take the inverse fft. Just wondering if anyone had any hands on experience so I wouldn't have to open matlab.

Reply to
Bobby Joe

Bobby Joe (him again!) writes

I noticed recently that Maxim, Linear Tech and maybe others do filters where you can shift the corner frequencies just by changing a resistor. Maxim favour switched-capacitor types, which I suspect have odd effects round their switching frequency(?) whilst Linear Tech have some truly magic looking ones based on clever op amp arrangements inside them. Perhaps the most extreme of these is the Linear Tech LTC1569 which is a

10th order(!) linear phase filter, you alter the cutoff freq by varying a resistor on one pin. Very pricey but good for specialist apps I imagine. A simple 8 pin device which looks easy to use. 
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Nemo
Reply to
Nemo

h
l
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I've listened to music that has gone through a sharp filter. It sounds kind of bad. As the music went up and down the scale, it sounded like the instruments where changed on the fly.

Reply to
MooseFET

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