TOPIC:

Can we get 1st order all pass added to multichannel Dirac boxes in PEQ 

We need 1st and 2nd order all pass to simulate crossover phase shift when running Dirac with crossovers off for multi-way 

then after Dirac calibration, we turn crossovers on and turn off the all pass filter to get perfect summation and linear phase behavior..

I’ve been using 2nd order all pass with Q.7 at crossover frequency to simulate a LR4 and it works perfect. 

Q1 for BW18 also

would be nice to get a 1st order all pass to do 2nd order slopes 

please add this to peq for all multi channel Dirac boxes 

thank you 

First-order all-pass can be added to the PEQ section of any miniDSP unit since day one.

Use this arrangement:

b0=-0.788336413521521
b1=1
b2=0
a1=0.788336413521521
a2=0

BTW, a second-order all-pass to simulate an LR24 crossover would be Q=0.5, not 0.7

Dave.

Thanks Dave , 

yeah I could never get the calculator to work off the spreadsheet 


it would be way easier if it was added as a PEQ option….. what frequencie center is that bi-quad ?


And , that’s strange , when I run the sim in rephase Q.7 lines up perfectly….
so is rephase wrong ? 

or , are you thinking of the Q of the magnitude characteristic? 

andrew 

You can modify the APF tab on the spreadsheet to generate a first-order coefficient.  This is not a bi-quadratic, so that's why it wasn't included, I guess.
That particular coefficient corresponds to a 1800Hz APF filter for 48khz.

I'm not sure about the rePhase computation.  I will check.
This is a totally flat magnitude response.  There isn't any Q to that. 

Dave.

Thank you 

yeah I just tried again

my excel is not cooperating 
it’s the online version (cooperate version)


please do verify 

yeah in rephase Q.7 overlay is exact to LR4 phase shift 


I meant the Q of the rolloff of the magnitude of a LR4 (which is .5) not the phase response 

I don’t know anything about Hilbert transform but you don’t want any maybe there’s a difference?

I’ll await your answer and verification!!!


Andrew 

Are you using the Minimum-Phase filters tab in rePhase???  Version 1.4.3?

When I select "2nd order All-pass" the phase response depiction is in error.  It shows a flat phase response for a Q=0.707, which is clearly incorrect.  It's incorrect for other Q settings as well.
This appears to be a bug in the rePhase program I hadn't noticed previously.  This needs to be reported to the author.

Anyways, to generate 1st-order all-pass coefficients use the bi-linear transform:
g = tan(pi*(Fc/Fs));  Where "Fc" is the cutoff frequency and "Fs" is the sampling rate.

b0 = (g-1)/(g+1);
b1 = 1;
b2 = 0;
a1 = b0;
a2 = 0;

You can invert polarity by flipping the sign in b0 and b1.

Dave.
 

dreite wrote:

Are you using the Minimum-Phase filters tab in rePhase???  Version 1.4.3?

When I select "2nd order All-pass" the phase response depiction is in error.  It shows a flat phase response for a Q=0.707, which is clearly incorrect.  It's incorrect for other Q settings as well.
This appears to be a bug in the rePhase program I hadn't noticed previously.  This needs to be reported to the author.

Anyways, to generate 1st-order all-pass coefficients use the bi-linear transform:
g = tan(pi*(Fc/Fs));  Where "Fc" is the cutoff frequency and "Fs" is the sampling rate.

b0 = (g-1)/(g+1);
b1 = 1;
b2 = 0;
a1 = b0;
a2 = 0;

You can invert polarity by flipping the sign in b0 and b1.

Dave.
Dave.


 

Dave, your the best I will try that!!! thank you


on the APF thing , no bug here... Ill just show you were your wrong. lol 

The magnitude has a Q of 0.5 and phase a Q of .7

Three pics, one is a overlay two others are single filters 




 

or snap you might be right 


look!!!

the LR4 in minimum phase then an overlay of linear phase....different shape!

I'll tell Thomas

WTH!!!!

Andrew

There's an intermittent idiosyncrasy in the rePhase program when displaying all-pass filter phase responses.  (I will characterize it further when I get a chance.)

Anyways, a first-order all-pass is easily applied in any of the miniDSP GUI schemes.  I've shown you how to do it.  Have fun.

Cheers,

Dave.

Thank you Dave !!!

as always amazing input 

(you did see my 2nd post?) I’m assuming your right for now until Thomas explains this bug I found / we found. 

thanks again Dave 

the LR4 in minimum phase then an overlay of linear phase....different shape!

I was not able to reproduce this behavior.
You probably forgot to disable the linear phase LR in your example.

BTW, a second-order all-pass to simulate an LR24 crossover would be Q=0.5, not 0.7

Why would it be 0.5?

pos wrote:

BTW, a second-order all-pass to simulate an LR24 crossover would be Q=0.5, not 0.7

Why would it be 0.5?
 

Because that's what the design objective was back in 1976 when Linkwitz and Riley came up with the scheme.
www.linkwitzlab.com/JAES/jaes_papers76.htm

Dave.

Dave, the paper does not describe an all-pass filter.

Please let me know exactly what you think is wrong with rephase's behavior.
 

If the two filter outputs are summed you'd create an all-pass filter.  The phase response of that filter should be equivalent to the system phase response of an LR24 crossover.  (for a second-order all-pass filter.)
Maybe we're just talking crossed-paths and this is a definition thing??
A practical experiment might illustrate this better??

Let me fiddle with rePhase more please.  I managed to get it in a very confusing state last night, but I may have had a setting in the wrong position.
Regardless, the Q-definition thing is not rePhase specific.

Dave.