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All Forums  Cool Edit  Parametric EQ Low/high Shelf

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Mark T Location: Norway Posts: 890	Posted - Tue Apr 22, 2003 3:58 am  While fiddling with the parametric eq just the other day (a new blues song?) I was looking at the low shelf cut off. I have a couple of questions I hope one of you guys can answer: My understanding is that the slider decides at what point the high pass filter starts cutting the bass, and that the slider on the left decides how sharp the bass roll off is. How am I doing so far? When I lower the left slider it doesn't create the kind of slope that I expect (the way it does in Ozones eq for example), so I can't create a sharp convex slope from 50 Hz, instead it creates a shallow concave slope and if I try to decrease it very much it starts pulling down the curve to the right of the shelf point (sorry if I am getting any terminology wrong here). Is this how it is supposed to work? _________________ Mark nil desperandum - nunc est bibendum
Syntrillium M.D. Location: USA Posts: 5124	Posted - Tue Apr 22, 2003 9:08 am  Though the slopes of a shelving filter can vary slightly, this is a pretty standard shelving curve. It sounds to me like you're looking to do a sharp cut-off, ie, hi-pass or low-pass. These filters (and their characteristics) are not the same (nor, obviously, the same sound) as a shelving filter. For that, you'd probably be best suited using the FFT filter, and if need be, you can visually (and easily) adjust the slope of the cut-off. ---Syntrillium, M.D. _________________
Mark T Location: Norway Posts: 890	Posted - Tue Apr 22, 2003 11:51 pm  Hi, Thanks for the response, if you take a look at the help for the parametric eq for Low Shelf Cutoff you will see why I got confused as it mentions low-pass filtering. I believe in Ozone there is a low-pass and high-pass filter included in their Parametric EQ so I guess I just assumed this was standard. Thanks for clearing it up.:) I have never used FFT filtering as I seemed to get what I needed from Pram. But I shall go and try it out. New toys:D _________________ Mark nil desperandum - nunc est bibendum
David Johnston Location: USA Posts: 39	Posted - Wed Apr 23, 2003 9:03 am  You can increase the low filtering steepness by putting the mid band there, and adjust it's Q setting... and even further by pressing the 'Band' button for the High Pass band (turning it from a high shelf to a band) and also moving it to the 40Hz area, and adjusting it's Q as well. You can get a very steep curve this way, if you have no need for the mid and high bands otherwise.
MusicConductor Location: USA Posts: 1524	Posted - Wed Apr 23, 2003 12:29 pm  I am guessing that Mark is asking about Parametric EQ in Effects/Filters/Parametric EQ and David is referring to the track EQ (which is also parametric) in Multitrack View. But the principle works well in both versions. I've created some powerful HPF / LPF configurations in track EQ in just the manner he's describing. The same will work in the Effect menu version as well. Use some of your bands--that's plural, as you can see--with a very narrow Q in the range you're wishing to cut, and it will give you a much sharper knife than the LFP/HPF sliders will. In some respects the FFT filter is less transparent to the sound, I presume? The parametric tools seem more accurate.
Mark T Location: Norway Posts: 890	Posted - Mon Apr 28, 2003 12:24 am  MusicConductor wrote: I am guessing that Mark is asking about Parametric EQ in Effects/Filters/Parametric EQ and David is referring to the track EQ (which is also parametric) in Multitrack View. But the principle works well in both versions. I've created some powerful HPF / LPF configurations in track EQ in just the manner he's describing. The same will work in the Effect menu version as well. Use some of your bands--that's plural, as you can see--with a very narrow Q in the range you're wishing to cut, and it will give you a much sharper knife than the LFP/HPF sliders will. In some respects the FFT filter is less transparent to the sound, I presume? The parametric tools seem more accurate. Hi Maestro, I am not quite sure what you mean by transparent to the sound, I was looking to boost the mid on a bass track and lose all the subsonics but when I dropped the low end on the param eq enough to get rid of the subs, it also lost some of the frequencies above. I did the job in the FFT filter and got a good clean result:D _________________ Mark nil desperandum - nunc est bibendum
MusicConductor Location: USA Posts: 1524	Posted - Mon Apr 28, 2003 3:37 pm  Believe me, the FFT filter is a great tool. What I mean by transparency is that a little phase shifting and ringing can be introduced into your audio, especially if the contour has any steep slopes. The Graphic Equalizer and Parametric Equalizer use a different approach (impulse response, I believe) that avoids these problems--but the filters are not as flexible. Everything involves tradeoffs!
Syntrillium M.D. Location: USA Posts: 5124	Posted - Mon Apr 28, 2003 4:09 pm  Mark T wrote: I did the job in the FFT filter and got a good clean result:D And that's why I initially suggested it, just from reading your initial inquiry. :) ---Syntrillium, M.D. _________________
DeluXMan Location: Canada Posts: 330	Posted - Mon Apr 28, 2003 4:12 pm  can you confirm that?... just to be sure i thought the following was the case: IIR [infinite impulse response] can have resonance and phase errors. FIR [finite impulse response] no phase errors Also: what transform(s) FIR? IIR? does the CEP FFT use, just for the record? I have been using the "scientific" low-pass, hi-pass functions for band limiting as it provides complete cutoff in the cut zone. There is a small boost at the cutoff frequency with high order settings though but sometimes this is good.
SteveG Location: United Kingdom Posts: 6695	Posted - Mon Apr 28, 2003 5:22 pm  DeluXMan wrote: can you confirm that?... just to be sure i thought the following was the case: IIR [infinite impulse response] can have resonance and phase errors. FIR [finite impulse response] no phase errors FIR filters can be constructed to be linear phase or not - usually they are, but it's not obligatory. IIR filters (ie using feedback techniques) can be made to ring, and there are also techniques for reducing the amount of non-linearity in them. Calling them phase 'errors' is a little misleading. All filters will have a phase shift, or delay associated with them - they wouldn't work otherwise. The critical part is the linearity of the shift, and that is where FIR filters are more likely to give a good 'musical' result. There is a little more info about FIR filters here. AFAIK, the CEP parametric filter is definitely IIR - it can ring. _________________
DeluXMan Location: Canada Posts: 330	Posted - Mon Apr 28, 2003 6:14 pm  Thanks SteveG. That link is excellent!! Ya phase error is a bad word! sorry. i guess phase shift is neither good nor bad, it's just there... The FIR has no phase "distortion" as descibed by the dspGURU though so a FIR filter might be usefull in the CEP toolbox.
David Johnston Location: USA Posts: 39	Posted - Mon Apr 28, 2003 11:55 pm  Cool Edit's FIR filters (FFT Filter, Graphic Equalizer, Resampling, Dynamics (Band Limiting) and Frequency Band Splitter) do not induce any phase shift, so you could think of them as more accurate in that respect. But, because they are FFT based, you need higher FFT sizes to get more resolution in the lower frequencies. The usefulness of zero-phase filters like this is that you can overlap a filtered signal with the original and not get any unwanted frequency notching or flanging. The IIR filters (Dynamic EQ, Notch Filter, Parametric Eqs and Scientific Filters) do have non-linear frequency-dependent phase shifting going on. Scientific Filters however does give the most control over the amount of phase shift. The IIR filters have the same resolution no matter what frequency you are working with, so the advantage over FIR is that you have more accuracy in working with very low frequencies. Also, with IIR you can get interesting ringing effects and edge-band boosting which might be useful for whatever reason (see the Notch Filter-Ice Cream Truck preset).
Mark T Location: Norway Posts: 890	Posted - Tue Apr 29, 2003 4:09 am  Thanks to all for your help and explanations:D _________________ Mark nil desperandum - nunc est bibendum
MusicConductor Location: USA Posts: 1524	Posted - Tue Apr 29, 2003 10:53 am  David (and Steve as well), thank you for that clarification. That ought to go in the help file!!! (Or is it already there? )
SteveG Location: United Kingdom Posts: 6695	Posted - Tue Apr 29, 2003 11:34 am  Somewhere there is another thread with the same info in it - I daresay that if you do a search for FIR using just David's name, you will find it. It has the same info in, I believe... _________________
MusicConductor Location: USA Posts: 1524	Posted - Tue Apr 29, 2003 11:59 pm  Well, sorry to say that "FFT," "IIR," and "FIR" searches don't yield such a post. (Thanks anyway, Steve.) So, this thread is now bookmarked!
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