All pass filter/ phase rotator frequency selection

Hi Guys,

  I am looking to play around with a phase rotator circuit to see how much it affects things such as a vocal, and a whole mix. I see that Orban use an allpass at 200Hz. I was kindly led to this in an earlier thread.


    http://www.w3am.com/8poleapf.html


  they use a frequency of 340Hz. DOes the frequency matter that much? Or, How do I re-calculate for 200Hz? How many poles - 4?


    Kindest regards, Any help most appreciated!



        ANdyP

The frequency is simply the -3dB frequency of the 10k/47n low-pass. To recalculate for 200 Hz you only have to change these values.
36k and 22n would give you about 200 Hz for example.

Can't give you any advice about the number of poles or how well that works. I think this is used in the final processing for broadcasting but I don't know any further.


Chris

Hi Chris,



  thank you very much! Simply explained too. I am keen to find out how this would screwup the sound of a vocal, and whether it is worth Phase-rotating elements of a mix which might cause problems in a radio mix. I would rather have this under MY control . . .


    Kindest regards,



      ANdyP

yes....very intresting for me too....have u ever seen this?

http://www.adt-audio.de/V700/Mastering/U790_Phasenschieber.html

I would change the capacitor value than the resistor. 10K is a standard value and makes it easier to scale it, beside the noise factor.

This is a good calculator site. http://www.sengpielaudio.com/calculator-RCpad.htm

If you want to do more detailed playing around I would highly recommend Don Lancaster's Active Filter Cookbook. It explains everything you ever wanted to know about filters in practical terms. It goes through scaling of each filter type. Very good book.