Convolution EQ

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sharke
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2017/12/20 06:14:22 (permalink)

Convolution EQ

Anyone used it? I watched a Groove3 tutorial recently in which they used an EQ that had fixed bands, and each one was based upon a convolution of the EQ bands on an analog console. Seems like a great idea on paper, but are they anything like they're cracked up to be? 

James
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    drewfx1
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    Re: Convolution EQ 2017/12/20 17:55:11 (permalink)
    sharke
    based upon a convolution of the EQ bands on an analog console 




    This just means it will match the frequency and phase response of whatever it was based on.
     
    But it's just a matching EQ curve - there's no distortion/saturation or anything that people often consider to be desirable analog processing.
     
    So if you think a given console has a "special" EQ curve, well OK. But it's just a particular EQ curve.

     In order, then, to discover the limit of deepest tones, it is necessary not only to produce very violent agitations in the air but to give these the form of simple pendular vibrations. - Hermann von Helmholtz, predicting the role of the electric bassist in 1877.
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    dmbaer
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    Re: Convolution EQ 2017/12/20 21:00:02 (permalink)
    As I understand it, a FIR (finite impulse response) filter is basically a convolution operation that stays in the time domain.  Convolution usually employs FFT conversions for efficiency's sake and FIR filtering does not, but either way it's convolution.  You can have a much longer set of samples involved when you go the FFT route, which is what is needed in convolution reverbs where there are sample lengths in the thousands.  Another way to put this is: convolution is essentially a filtering operation in the first place.
     
    There's a bit of snake oil on sale here it would appear.
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    drewfx1
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    Re: Convolution EQ 2017/12/20 23:17:09 (permalink)
    dmbaer
    As I understand it, a FIR (finite impulse response) filter is basically a convolution operation that stays in the time domain.  Convolution usually employs FFT conversions for efficiency's sake and FIR filtering does not, but either way it's convolution.  You can have a much longer set of samples involved when you go the FFT route, which is what is needed in convolution reverbs where there are sample lengths in the thousands.  Another way to put this is: convolution is essentially a filtering operation in the first place.
     
    There's a bit of snake oil on sale here it would appear.




    Yes, an FIR filter does straight convolution in the time domain (or something mathematically equivalent). And an IIR (infinite impulse response) filter - like an analog EQ - can be implemented as an FIR filter just by taking the impulse response and convolving it with your signal (because in the real world the impulse response isn't infinite), though FIR filters are less efficient. 
     
     
    But personally I wouldn't call it "snake oil" unless they are misleading people by implying it's magically more than accurate reproduction of EQ curves (and I haven't actually seen what their marketing says). But then I also grade on a curve and sort of give a pass to companies that rely on their audience to read things into their marketing that they never actually explicitly say.

     In order, then, to discover the limit of deepest tones, it is necessary not only to produce very violent agitations in the air but to give these the form of simple pendular vibrations. - Hermann von Helmholtz, predicting the role of the electric bassist in 1877.
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    sharke
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    Re: Convolution EQ 2017/12/21 00:12:58 (permalink)
    I don't think anyone's suggesting it's anything more than a way to accurately reproduce an EQ curve. I just find it interesting that we can do that now, and wonder whether the results are good. 
     
    Here's an example of what I was talking about - I've heard people raving about it and then saw it used in a mixing video the other day. http://www.acustica-audio...tuemart&Itemid=189

    James
    Windows 10, Sonar SPlat (64-bit), Intel i7-4930K, 32GB RAM, RME Babyface, AKAI MPK Mini, Roland A-800 Pro, Focusrite VRM Box, Komplete 10 Ultimate, 2012 American Telecaster!
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    drewfx1
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    Re: Convolution EQ 2017/12/21 01:07:32 (permalink)
    sharke
    I don't think anyone's suggesting it's anything more than a way to accurately reproduce an EQ curve. I just find it interesting that we can do that now, and wonder whether the results are good.

     
    Reproducing an EQ curve accurately is easy - you take the impulse response and convolve it with your signal. The only downside is convolution is relatively costly in terms of processing power. Linear phase EQ's are FIR = convolution = more CPU intensive vs. typical EQ's which are generally IIR.


     
     
    The Acustica stuff is different though and is not what we were talking about. They have been doing a non-linear variant of convolution:
     
    http://www.acustica-audio.com/index.php?option=com_content&view=article&id=14&Itemid=2471
     
    That allows for stuff other than just the frequency and phase response to be recreated. It is CPU heavy though.

     In order, then, to discover the limit of deepest tones, it is necessary not only to produce very violent agitations in the air but to give these the form of simple pendular vibrations. - Hermann von Helmholtz, predicting the role of the electric bassist in 1877.
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