Re: [LAU] Wah update

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To: <linux-audio-user@...>
Date: Monday, July 20, 2009 - 9:57 am

On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken Restivo wrote:

> Just a quick update on the wah research.

AFAICS this is a resonant (which is not the same as bandpass) filter.
If the response near Fs/2 bcomes flat, that does not mean it is a
highpass.

Remember that any digital filter is 'mirrored' to the other side
of Fs/2. Also the magnitude of the response must be continuous or
zero at all points (for finite order).

The result of all this is that at Fs/2 the response must be either
zero or have a zero derivative, i.e. be horizontal.

In a high order filter you can make the 'roundoff' region near
Fs/2 very small, but it's always there, unless the response is
zero at that frequency.

You can probably get this type of response using the MOOG VCF
by taking the output at a different point in the algorithm.

The MOOG VCF is 4th order, this is overkill as the analog
circuit is very likely to be just 2nd order.

Ciao,

--
FA

Io lo dico sempre: l'Italia รจ troppo stretta e lunga.

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Messages in current thread:
[LAU] Wah update, Ken Restivo, (Mon Jul 20, 3:11 am)
Re: [LAU] Wah update, Andres Cabrera, (Mon Jul 20, 1:07 pm)
Re: [LAU] Wah update, Fons Adriaensen, (Mon Jul 20, 10:59 pm)
Re: [LAU] Wah update, Fons Adriaensen, (Mon Jul 20, 9:57 am)
Re: [LAU] Wah update, Ken Restivo, (Tue Jul 21, 12:12 am)
Re: [LAU] Wah update, Bill Allen, (Thu Jul 23, 10:21 pm)
Re: [LAU] Wah update, Carlos Sanchiavedraz, (Tue Jul 21, 3:56 pm)
Re: [LAU] Wah update, Ken Restivo, (Fri Aug 14, 8:00 pm)
Re: [LAU] Wah update, hermann, (Sat Aug 15, 12:14 pm)
Re: [LAU] Wah update, Arnold Krille, (Fri Aug 14, 8:43 pm)
Re: [LAU] Wah update, Folderol, (Fri Aug 14, 9:19 pm)
Re: [LAU] Wah update, Ken Restivo, (Fri Aug 21, 12:22 am)
Re: [LAU] Wah update, Folderol, (Fri Aug 21, 10:12 pm)
Re: [LAU] Wah update, James Cameron, (Fri Aug 21, 12:29 am)
Re: [LAU] Wah update, Fons Adriaensen, (Tue Jul 21, 1:44 pm)
Re: [LAU] Wah update, Paul Coccoli, (Wed Jul 22, 8:18 pm)
Re: [LAU] Wah update, Julien Claassen, (Mon Jul 20, 6:11 am)
Re: [LAU] Wah update, Ken Restivo, (Mon Jul 20, 6:48 am)
Re: [LAU] Wah update, Julien Claassen, (Mon Jul 20, 7:46 am)
Re: [LAU] Wah update, Justin Smith, (Mon Jul 20, 4:32 am)
Re: [LAU] Wah update, Ken Restivo, (Mon Jul 20, 5:25 am)
Re: [LAU] Wah update, Justin Smith, (Mon Jul 20, 5:33 am)
Re: [LAU] Wah update, Justin Smith, (Mon Jul 20, 5:37 am)