| "There is a tradeoff between steepness and stability,
so in certain designs too steep a shelf can make a filter
that will "blow up" with some inputs"---
If recall,... that is a result of the Gain-Bandwidth product
of a filter circuit. And I think Barkhausen's criteria played
a part in it as well. They "blow up" or they turn into very
noisy oscillators.
I've built hardware versions back in the day, and when a filter-Q
or resonance gets too high and breaks into oscillation, it sounds
awful. Could be functionally useful in rare circumstances to add
color by adding noise, but only in small and controlled amounts.
Cheers,
-Partev
============================================================
--- noisesmith@gmail.com wrote:
From: Justin Glenn Smith
To: csound@lists.bath.ac.uk
Subject: Re: [Csnd] using parametric EQ
Date: Fri, 30 Dec 2011 13:18:00 -0800
The standard behavior of Q on a shelving filter is to control the steepness of the shelf. There is a tradeoff between steepness and stability, so in certain designs too steep a shelf can make a filter that will "blow up" with some inputs. Also it can be useful aesthetically to have a gradual cutoff rather than a steep pass band on a filter.
richard duckworth wrote:
> peaking mode appears to work like a normal parametric eq, as you say, it boosts/cuts a range of frequencies around a centre frequency - the 'width' of the range is determined by the value of Q.
>
> 'shelving' mode appears to implement low & hi shelf filters. Your description of low shelving is correct, though a plot of the frequency response of a euphonic shelf filter would appear to curve gently between the boosted ( or cut) portion and the area above Fc.
>
> I implemented a demo of pareq in QuteCsound with an fft display and widgets to vary the parameters: Fc seems to exhibit strange behaviour towards the extremities of the 20-20kHz frequency span. I'll try the others next.
> All the best, Rich
>
>
>
> ________________________________
> From: Dennis Raddle
> To: csound@lists.bath.ac.uk
> Sent: Monday, 26 December 2011, 22:55
> Subject: [Csnd] using parametric EQ
>
>
> Can someone explain the parametric EQ opcode to me (pareq).
>
> Does "peaking" mode mean that it boosts (or cuts) frequencies around a center frequency and leaves the rest of the spectrum intact?
>
> What does "low shelving" and "high shelving" mean?
>
> I'm guessing that low shelving means it boost or cuts everything below the corner frequency and leaves everything above it alone. And the shape of the boost or cut is flat. So the response would look like a stairstep. Is this right?
>
> What does Q mean in the shelving mode?
>
> Thanks,
> Dennis
> Send bugs reports to the Sourceforge bug tracker
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>
>
Send bugs reports to the Sourceforge bug tracker
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_____________________________________________________________
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