SynthMaker

Linear Phase EQ (bidirectional IIR)

Archive · 2013 4 old posts

From the original SynthMaker forum (2004–2014), with its members’ names and dates.

J.riddell ·

Hi there, I've inverted some biquad coeficients like interchanging the "0" by the "2" and the a by the b...and one resulted on a amplitude invertion and the other in a phase invertion (I saw it in the tool for graphing the response of a biquad filte included in synthmaker). So I got exited because theorically one can put on series two equal amplitude response but inverted phase will give a linear phase filter. Unfortunately it didn't work when introduced those coeficients to a band of the param eq component that comes with synthmaker. And then I went to google to investigate and found this topic. And you did it!.

Now I made a gui for this. I hope I have not done anything bad doing that 😕 .

I added a control for each band to have a normal (Fwd), inverted (Bwd) or flat (Fwd&Bwd) phase response...every sounds diferent and can play combining them.

And problems I had: -I don't know well how works the inverter so I could not enlarge the buffer more than 16384. -Seems that in some hosts is problematic to change the delay compensation so it would be needed to send a fixed static buffer in the vst. -When I move the controls fast sometimes sound a loud dangerous and unpleasant sound, that happen because of the desynchronization between the coefficients, and that causes that the eq have by a momet a strange curve and add a lot of gain to a certain frequency (like 30dB). By that y put clearing audio when moving controls...but that didn't solve the problem entirely, and by that I put a panic button that cleares audio.

Now the Links to the material made by others in the forum

Knobs And switches [old link]

The display/drag/edit box (Drag Horizontally) to control the frequency is a modification of the display edit here [old link]

And the Slider for the buffer were in this topic AyePedro! (now for 1.7 as well)

Well...is the first time I do something like this. I hope you like or find useful.

Xtinct ·

Nice gui and nice combining of all the topics mentioned. No you have not done anything bad this is how the forum works, some one puts forward an idea and then others either refine it or take it a step further as you have done good work keep it up. P.S. you don't have to show where everything came from just a thanks to the original authors will suffice.

MegaHurtz ·

This looks in the direction, but how much is the delay and stuff? Suposedly infinite right. "Not going to say It's not really iir and such" well a little 😉

Been thinking if its possible to track the impulse comming from the top down, turn the impulse response inside out so to say. But in this scenario it does raise the possibility to reverse the sample and get a neat filter as well, may try it one day. Mindless to say your ears probbably cant do this trick.

Oh and suspended between logarithm liniar filters can do this as well. But thats kind of a hard stopping fir as well. well 😉

MegaHurtz ·

Oh I see.. Hahah 2012.. These diggers dig deep diggers they are.

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