TOPIC:

POS,

In post 393 

i overlayed a minimum phase lr4 

then turned on a linear phase LR 4 


different attenuation 


andrew 

The Q of a 2nd order LR is indeed 0.5, but a 4th order LR is the sum of two 2nd order filters with a Q of 0.707.

So that linear phase overlay is something else ? 

Andrew, I addressed this post of yours in my first response here .

Ah ha

yes it was cascading it!!!

it works fine 


sorry I was so worried about the APF thing…  


okay!!! It’s settled !!


thank you sooo much for helping us!! 

andrew 


 

So DevTeam 

I can’t get spreadsheet to work 

it would be so much simpler if AP1 was added to peq 

I tune “ a lot” of car dsps , I have my clients buy 8x12DLs and I tune them.  Almost all 8x12DLs sold in Colorado were probably tuned by me. 


it would really streamline things and for the hundreds of ppl I help online set there dsp up, would be easy if AP1 was added as this tuning method with DL is the choice way and 2nd order slopes have superior advantages in a car where drivers are not mounted close together. 

thank you ,

Andrew 

pos wrote:

The Q of a 2nd order LR is indeed 0.5, but a 4th order LR is the sum of two 2nd order filters with a Q of 0.707.

 

Careful.  Summing is different than cascading.

Originally, when the LR24 crossover was devised, two second-order Butterworth sections (-3db, Q=.707) were 'cascaded.'  The net result is -6db, Q=0.5.
Two adjacent (summed) filters with that characteristic create an amplitude response that is flat, but with a phase response equivalent to each filter section.
This is an important distinction.

Now that I look at rePhase further, I think it is depicting the correct phase response associated with the Q setting of a second-order all-pass filter.
Notably, and appropriately so, you don't label the second-order all-pass settings with either BW or LR24, but only with a user-defined Q setting.

I can't seem to recreate what I was seeing last night when fiddling with the program.  I must have had something effed up in the settings because it was showing me a completely flat (linear) phase response when viewing a second-order all-pass filter on the minimum-phase filter tab.  I was not in the 'compensate' mode or anything.  Puzzling.

I'm not sure how the topic of linear-phase entered (from denver) this conversation.  Nothing about Linkwitz-Riley filtering is linear-phase.

Dave.

Careful.  Summing is different than cascading.

Originally, when the LR24 crossover was devised, two second-order Butterworth sections (-3db, Q=.707) were 'cascaded.'  The net result is -6db, Q=0.5.

Nitpicking on words? 
Then let me emphasis that a single Q has no meaning for a 4th order filter 
Anyway, the fact remains that the corresponding 2nd order all-pass filter has a Q of 0.707 and not 0.5, and that is what is implemented in rephase.

To be clear, I am not saying rephase is free of potential bugs, but I don't think such blatant errors as the ones described here (wrong Q, wrong magnitude) would have stayed unnoticed for 10 years. 

Nitpicking?  No, I'm being precise.
And we're not talking about any 4th-order filter.  We're talking about a specific one, which can indeed be characterized by a single Q value defining the phase response.
Your own program demonstrates that! 

I just got through telling you that rePhase IS portraying the phase-response of an all-pass filter correctly....and that the issue must have been pilot error on my part!!
And please spare me the rhetoric regarding blatant errors that went unnoticed for 10 years.
You've created a great utility here.  There's no need to get defensive for no reason.

Dave.

Dave ,

no offense, but you opened your response with the phrase “be careful” lol 

it was a little bit nit picking ish 

Cascading two filters and summing two filters are different (duh) 

I was cascading two filters , that’s why I got double the attenuation, and thought it was an error….. I was wrong 


anyway…… don’t feel bad you’re not the only one that tried thinking that the Q was .5 , i’ve been confronted about that on other forms. I suppose it’s a easy one to think would be different.
 

I'm not feeling bad at all. 

I think you should be careful too. 
When cascading two identical filter sections you do indeed get double the attenuation, out of band.  (As an example.....this is what gets you from a 12db/octave slope to a 24db/octave slope.)

Summing and cascading are two different things.
When you say "Cascading two filters and summing two filters are different (duh)", I'm wondering what your "duh" means.  If you "got it" or if you didn't?

An example:
If I take two identical filters and sum them I get the blue response.
If I take two identical filters and cascade them I get the black response.

The essence of creating various LR filters was/is cascading of second-order filter blocks.

I'm not trying to get in the weeds on this, but the terminology is important.

Dave.
 

Dave as I said 

and I know the difference, 


i  cascaded Two filters , a linear phase LR4 and a minimum phase LR4 (that was my mistake in thinking there was a bug ) 

my terminology was correct , is correct , and I won’t “be careful” as that is basics……( your nit picking and trying to make me feel like I used the wrong terminology when in fact I did not)

and I almost never use the term “summing” unless I’m in the acoustical arena…. With extra emphasis on the word almost


I learned my terminology from the MECP master tech study guide , where I got certified. I’ll continue to use that terminology. 

'Next time you think I might be feeling bad, rest assured, I'm not.
You're welcome to speak for yourself to other forum posters, but don't speak for me.

Keep those two things in mind, and we'll be fine.

Dave.

That works 

I’ll never speaker for you ever ever ever 


I hope to speak with you tho (dam dood your wikked smart I don’t want to loose a online friend over something silly) 

Here you go:

Dave.