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Author Topic: Active Filtering  (Read 2199 times)

rlebrette

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Active Filtering
« on: June 26, 2012, 02:26:56 pm »

I'm not expert in the domain, so please, don't shoot me :)
I've a friend of mine (a recent MC user) who owns a stereo system based on 2x4 horn loudspeakers. He would like to do active filtering via MC.
We have started to implement the solution based on the features provided by MC.
In the Parametric Equalizer (PE) we have separated the stereo channels on 2x4 channels.
Next, we have started to filter each channel with the integrated filters. But he find that the available filters are not enough satisfying, he would like to apply linkwitz-riley with a 18dB slope.
Is there any way to achieve this kind of filtering with MC? Is there any plugin that he can use to integrate in the DSP chain?
Any help or walk-through is welcome.
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Matt

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Re: Active Filtering
« Reply #1 on: June 26, 2012, 02:41:41 pm »

Linkwitz is available in Parametric Equalizer.

I've considered adding a way to add a generic biquad (a0, a1, a2, b0, b1, b2), but it's so advanced I don't know if it's a good idea.

You can use tools like this to build those biquads:
http://www.minidsp.com/images/fbfiles/files/All_digital_coefs_v1-20101026.zip
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Matt Ashland, JRiver Media Center

mojave

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Re: Active Filtering
« Reply #2 on: June 26, 2012, 03:31:17 pm »

Is there any way to achieve this kind of filtering with MC? Is there any plugin that he can use to integrate in the DSP chain?
Any help or walk-through is welcome.
The filters in JRiver are Butterworth filters. You can cascade two Butterworth filters to make a Linkwitz-Riley filter by adding two identical high or low pass filters. However, you won't be able to get an exact 18 dB filter.

Voxengo's GlissEQ is a VST plugin that lets you approximate several filter types by changing the Q of the filter. It used a 64-bit audio path like JRiver and also allows for multiple channels.

A more automated method would be to use Audiolense and the convolution engine in JRiver. 

Quote from: Matt
Linkwitz is available in Parametric Equalizer.
The Linkwitz Transform isn't the same as a Linkwitz-Riley 18 dB filter that rlebrette inquired about.
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rlebrette

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Re: Active Filtering
« Reply #3 on: June 27, 2012, 08:15:05 am »

The filters in JRiver are Butterworth filters. You can cascade two Butterworth filters to make a Linkwitz-Riley filter by adding two identical high or low pass filters. However, you won't be able to get an exact 18 dB filter.

Voxengo's GlissEQ is a VST plugin that lets you approximate several filter types by changing the Q of the filter. It used a 64-bit audio path like JRiver and also allows for multiple channels.

Thanks I've downloaded the VST and it works fine in MC, we are going to check if it's satisfying the requirements.

A more automated method would be to use Audiolense and the convolution engine in JRiver. 

I know that, and I'm also an Audiolense user, but my friend would like to test other solutions before investing in it.

The Linkwitz Transform isn't the same as a Linkwitz-Riley 18 dB filter that rlebrette inquired about.

Indeed, that's what I've discovered, the Linkwitz Transform is more targeted to improve bass on systems.
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natehansen66

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Re: Active Filtering
« Reply #4 on: June 27, 2012, 01:33:44 pm »

But 3rd order LR type filters don't exist  ?

A 3rd order BW could be had using the 2nd order BW filter and a shelving filter. Don't be afraid to use peaks/notches as well to get the desired output.
 
A 1st order hp/lp filter as well as hp/lp filters with user definable Q values would make MC's PEQ about perfect  ;)
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