Re: [SoX-users] SoX plot coefficients

[Sergei S. <ser...@ya...>]

----- Original Message -----
> From: Ulrich Klauer <ul...@ch...>
> To: sox...@li...
> Cc: 
> Sent: Saturday, December 15, 2012 3:29 AM
> Subject: Re: [SoX-users] SoX plot coefficients
> 
> Marco Bandiera <mar...@gm...>:
> 
>>  Where could I find the formulas for coefficients a1, a2, b0, b1, b2?
> 
> I'm not sure what you are looking for, but if you want to calculate a*/b* 
> from the filter frequency and bandwidth etc., the description is here: 
> http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
> 
> Ulrich
> 

SoX assums B(z)/A(z) (_not_ A(z)/B(z)) form:

"
       biquad b0 b1 b2 a0 a1 a2
              Apply a biquad IIR filter with the given coefficients. Where b* and a* are the numerator and denominator coefficients respectively.

              See http://en.wikipedia.org/wiki/Digital_biquad_filter (where a0 = 1).

              This effect supports the --plot global option.
".

Both B(z)/A(z) and A(z)/B(z) can be seen in different textbooks.

Regards,
  Sergei.