Filter different orders?

Discussion in 'Effects and the DSP' started by emigrante, Apr 23, 2009.

  1. emigrante

    emigrante New Member

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    hi

    i'm new @ using the kx-software. my english is not very good, so
    i hope everyone understands my problem.

    i would like to put a subsonic filter to my subwoofer.
    unfortunately there are only 2 types of filters.
    the crossover 2th und 4th order, which is not practical, because
    you only can choose 40 hz @ 12/24dB. the other one is the eq-filter
    with this "Q-factor" which does not make sense to me. by the way you can
    only choose 20hz which is sometimes a bit to high.
    i do not understand how this Q-factor works.

    so my question is: is it so difficult to programm
    a filter in which you can choose a frequenz from 10 to 20.000 hz,
    an choose the slope from 6 to 24 dB?
    does somebody work on it? does it make sense to wait for it?
    or should i look for other solutions ?

    i hope somebody can help me.
    thanks for your time and reading !

    greez,
    tim
     
  2. stylus02

    stylus02 New Member

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    the eq- lowpass works well. you should split the signal into 2 pathes. give one path into the lowpass (to subwoofer) and the other into a eq- highpass (to mid/high speakers). set both frequencies to same value. the q- factor means the amplification of the frequency you have choosen. you can boost the bass extremely, when q is high.

    stylus
     
  3. emigrante

    emigrante New Member

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    AW: Filter different orders?

    danke/thanks ;)
    but this was not my question.
    a need a highpass for my subwoofer, so it works like a subsonic.

    ( gerne in german per pn :D )
     
  4. stylus02

    stylus02 New Member

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    Re: AW: Filter different orders?

    let's try in english again (could interest all kx- users in the world ;) ). i had to read about a subsonic- filter: it's a highpass with preferable high slope. the kill of lowest frequencies should protect the subwoofer from high ampitudes. i knew the term "rumble filter" or "lowcut filter". you can use the eq- highpass with low setting the cutoff. if i'm right it's a second order biquad. this is good enough. also try the q- factor to boost or cut the amplitude of cutoff- frequency. (it virtual changes the slope of the filter)
    if you want cut high frequencies too, because your subwoofer has no build-in lowpass, you have to put the eq- lowpass after the highpass. all in all you get a bandpass- structure with a great variable range (better that a fixed bandpass)

    stylus
     
    Last edited: Apr 24, 2009
  5. emigrante

    emigrante New Member

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    AW: Filter different orders?

    yes i know, but the lowest frequenz, which you can choose is 20hz, i think.
    thats too high. and this q-factor is a horror.:rolleyes:

    by the way: i need 6 dB filters also.
     
  6. stylus02

    stylus02 New Member

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    Re: AW: Filter different orders?

    i think this could help you. (german tread)

    Subsonic Filter- was macht er genau? - Hifi Basiswissen / Fachwissen - CarHifi Forum / Autohifi Forum / Hifi Forum

    also take a look at earlier treads. some people have made plugins for multi-speaker setups with crossover filters, latency compensation and more.

    again, the cutoff- frequency means the frequency, where the signal amplitude goes down -3db. of course lower frequencies have more loss on amplitude, if we look at the highpass. you can imagine the slope as a rise of a mountain. (there are no real filters with infinite slopes.) the mountains body is the frequency- range which can pass. everthing around it you will not hear.

    and here we have a nice rendering of a 12 db highpass.
    http://www.beis.de/Elektronik/AudioMeasure/Images/FRHighPass.GIF

    to come back to your wish to set lower cutoff- frequencies than 20 hz. it's not really useful to to this, because the effect becomes smaller and smaller, if we stay on a 12 db highpass. the effect on 6db highpass would be smaller again.

    conclusion: we need more than 2 orders to have higher slope. you can try to attach more highpass- filters in series to increase the order of the filter- structure.

    stylus
     
    Last edited: Apr 24, 2009
  7. emigrante

    emigrante New Member

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    AW: Filter different orders?

    ähm. i know what a subsonic filter does.
    and thats the point. a subsonic @ 40 or 20 Hz does not make sense, becuase
    it cutts to much from the higher frequenzes.

    36 dB @ 10 or 15 hz would be the optimum. anyway, the 6db and 18db filter
    is also missing.
    and i knwo the point with the -3db. it is the piont where the maximum
    signal-power goes down by a factor (in german) "wurzel2".


    so to clarify the situation:
    i do not want to set a 6db subsonic!
    the 20hz is to high for me. i would like to set it @ 10 or (max) 15hz but
    with 24 or 36dB.

    but a 6db HP crossover would be in some situations very good for the
    tweeter e.g.

    thanks for your help !

    greez,
    tim
     
  8. GnuBeatz!

    GnuBeatz! New Member

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    AW: Filter different orders?

    Hi!

    I am also searching for a plugin with 6dB/octave and 18dB/octave crossovers.
    Could it be possible that there is one available meanwhile?

    Thanks in advance, Fabian!
     
  9. WxMan1

    WxMan1 Active Member

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    Q= f_ctr / (f2 - f1), where f2 & f1 are -3db corner freq.

    EDIT: Its come to my attention that I must revise and extend my previsou answer; the notch filter I previously [now redacted] is actually a quite poor choice for sub-sonic filtering (based on the freq response of notch filters). Its much better to use a high-pass filter for sub-sonic filters. Unfortunately on is dependent on the 2nd order nature of such filters (12 dB/ octave). While one can implement a 4th-order cross-over, the increased roll-off at the -3 dB gain at the cross-over is offset by progressive gain attenuation to 1.7 of corner frequency. This may be an unacceptbable frequency response. To counteract the roll-off leading up to the corner frequency 50% power level (i.e., -3 dB gain), one has to implement a EQ peaking plug-in in series post the 4th-order cross-over and customize the center freq and associated -3 dB corner freq via Q setting of the EQ peak filter. The EQ peaking filter allows one to define the gain + / - between the corner frequencies F1 & F2.

    The formula to define Q is per the above description. One can solve algebraicaly for any of the unknown values. The resonant frequency for band-pass filters - including EQ peak - is obtained by SQR( F1 * F2). The difference of F1 & F2 is the bandwidth. So to offset the -3 dB rolloff leading up to the 4th order cross-over cut-off transition region, one has to define the precise corner frequencies and the specific gain required to augment the overall freq response.

    To get a handle on this implement the Wave generator feeding signal of desired freq and gain into the plug-in of interest. Output should then be to a peaking plug-in. I've found that's its much easier to run high-pass filters in series w/ Q = 0.75 to accomplish that.

    FWIW: -96 dB is CD quality signal to noise ratio (about as quiet as one can hope to accomplish). Futhermore, -3 dB is 50% of maximum amplitude power. So a -20 dB gain at some arbitrary cut-off freq should be fairly satisfactory (given subsequent 2nd (or even 4th) order roll-off from there; if necessary, use EQ peaking as a filtering adjunct to boost gain precisely in the bandwidth required.

    Here's a link to some information about Q:

    http://www.beis.de/Elektronik/AudioMeasure/UniversalFilter.html

    http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm
     
    Last edited: Jul 23, 2010
  10. Kermet

    Kermet New Member

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    AW: Filter different orders?

    ist there now a solution for 1st order crossovers (6 dB filter)?
     
  11. WxMan1

    WxMan1 Active Member

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    There aren't any 1st order plug-ins. Although I believe that can be accomplished via bandpass filter, in that the 2nd order roll-off rate must be shared by both skirts of the pass-band.

    ALSO, I'm drawing attention to the fact that I've radically revised my orginal post on tnis thread.
     
  12. Kermet

    Kermet New Member

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    AW: Re: Filter different orders?

    you could also use RMAA to plot the frequency response:
    RightMark Audio Analyzer. Products. Audio Rightmark
     
  13. Russ

    Russ Well-Known Member

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    That is not really practical to do in the DSP. Slope is determined by the order of the filter, and different order filters require a different number of registers and a different number of instructions.

    e.g.
    Using such a plugin set to 12 dB/Ocatve (for example), would be basically the same as loading EQ Lowpass (for example) twice in the DSP, but only using one of them (while still consuming the (limited) DSP resources of both).
     

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