>On Mon, 18 Feb 2008 16:35:31 -0600, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:
>
>>> You know, Vlad, you are the only one who picked up on carleeto's 
>>> fundamental misconception. The rest of read "Linkwitz-Riley" and just

>>> assumed he _meant_ crossover. Good catch!
>
>I have actually designed multiband dynamics processors using crossover
topologies.  Extension of the concept to EQ was not
>difficult.  I figured the OP wanted something akin to the
Bass/Presence/Treble controls on old-time preamplifiers.

That is exactly what I was looking for. In fact, that is also what I was
designing - a simple set of Bass/Presence/Treble controls for use during
playback in the auditorium. 

I found a lot of useful info here :
http://www.planetanalog.com/article/printableArticle.jhtml?articleID=12802683

I was able to use a Linkwitz-Riley crossover topology to achieve this. I
believe the result would be a shelving EQ. 

Thank you for all your help. 

>On Tue, 19 Feb 2008 16:15:09 -0600, "carleeto" <carleeto@gmail.com>
wrote:
>
>>However, if I do split it, could I use two LR crossovers to split the
>>input stream, then sum their outputs and apply boosts/cuts to
effectively
>>synthesize a 3 band EQ?
>
>Only if you also include the allpass compensation detailed in the
>D'Appolito paper that I referenced in an earlier reply.
>
>Greg
>

Thanks Greg. Will have a look at it. 

On Tue, 19 Feb 2008 16:15:09 -0600, "carleeto" <carleeto@gmail.com> wrote:

>However, if I do split it, could I use two LR crossovers to split the
>input stream, then sum their outputs and apply boosts/cuts to effectively
>synthesize a 3 band EQ?

Only if you also include the allpass compensation detailed in the
D'Appolito paper that I referenced in an earlier reply.

Greg

>Thank you. I would like to be able to boost and cut. Would the Audio EQ
>Cookbook (http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt) be of any
>help in this case? I guess I would be looking for a shelving EQ. Is
there
>a better candidate I could use? At present, I'm not thinking about
>splitting the sound stream, just processing it.
>
>However, if I do split it, could I use two LR crossovers to split the
>input stream, then sum their outputs and apply boosts/cuts to
effectively
>synthesize a 3 band EQ?
>
I do realize there might be a few things wrong with my understanding.
Please do let me know what they are so I could learn. Thank you so much
for all your responses. They have really helped a lot. 

Thank you. I would like to be able to boost and cut. Would the Audio EQ
Cookbook (http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt) be of any
help in this case? I guess I would be looking for a shelving EQ. Is there
a better candidate I could use? At present, I'm not thinking about
splitting the sound stream, just processing it.

However, if I do split it, could I use two LR crossovers to split the
input stream, then sum their outputs and apply boosts/cuts to effectively
synthesize a 3 band EQ?

On Mon, 18 Feb 2008 16:35:31 -0600, Vladimir Vassilevsky <antispam_bogus@hotmail.com> wrote:

>> You know, Vlad, you are the only one who picked up on carleeto's 
>> fundamental misconception. The rest of read "Linkwitz-Riley" and just 
>> assumed he _meant_ crossover. Good catch!

I have actually designed multiband dynamics processors using crossover topologies.  Extension of the concept to EQ was not
difficult.  I figured the OP wanted something akin to the Bass/Presence/Treble controls on old-time preamplifiers.

>> The important fearure od LR crossovers is that there is no cancellation 
>> of frequencies in the crossover region anywhere in a typical auditorium. 
>> Although a LY is allpass for voltage, it has a 3 dB power dip,
>
>Yes! Although it took me a minute to figure out why :)

I had never thought of it that way before, Jerry.  For those who haven't figured out why:

Power output from lowpass section (limiting case; assume highpass output = 0):  
V&#4294967295;/R.

Power output from highpass section (limiting case; assume lowpass output = 0):  
V&#4294967295;/R.

Combined power output at crossover, LP and HP section each receiving V/2:  
(V/2)&#4294967295;/R + (V/2)&#4294967295;/R = V&#4294967295;/4R + V&#4294967295;/4R = V&#4294967295;/2R.

>I'd say the crossover filter response is not very important. The 
>arrangement and the response of the speakers and the acoustics of the 
>room have much higher influence. As for the crossover, Bessel, 
>Butterworth, LR or any other kind of filter with the slope of ~24dB/oct 
>will do about equally as good.

In the living room the differences are not nearly as important as they are in the auditorium, where phase differences between LP
and HP sections lead to very audible lobing problems.

Greg

Jerry Avins wrote:

> Vladimir Vassilevsky wrote:
>> carleeto wrote:
>>
>>> I have read a lot about the good phase response of the Linkwitz-Riley
>>> filter and would like to design a 3 band equalizer using it.
>>
>>
>> ????
>> LR as equalizer does not make sense.
>>
>> LR is a hipass/lopass crossover arrangement made of four Butterworth 
>> stages (two as lowpass, another two as highpass). There is nothing 
>> particularly good about the phase response. The feature of LR is that 
>> the sum of the highpass and the lowpass channels makes for the perfect 
>> allpass; although it is largely unimportant in practice.
> 
> 
> You know, Vlad, you are the only one who picked up on carleeto's 
> fundamental misconception. The rest of read "Linkwitz-Riley" and just 
> assumed he _meant_ crossover. Good catch!

Actually, Greg made a good point about the in-phase addition of the 
different bands. If the equalizer is made as the parallel combination of 
the bandpass filters, the LR-like arrangement avoids the possible dips 
in the areas of overlap.

> The important fearure od LR crossovers is that there is no cancellation 
> of frequencies in the crossover region anywhere in a typical auditorium. 
> Although a LY is allpass for voltage, it has a 3 dB power dip,

Yes! Although it took me a minute to figure out why :)

> which I 
> think is more important -- as a defect -- in a typical living room.

I'd say the crossover filter response is not very important. The 
arrangement and the response of the speakers and the acoustics of the 
room have much higher influence. As for the crossover, Bessel, 
Butterworth, LR or any other kind of filter with the slope of ~24dB/oct 
will do about equally as good.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Vladimir Vassilevsky wrote:
> 
> 
> carleeto wrote:
> 
>> Hi Everyone,
>>
>> I have read a lot about the good phase response of the Linkwitz-Riley
>> filter and would like to design a 3 band equalizer using it.
> 
> ????
> LR as equalizer does not make sense.
> 
> LR is a hipass/lopass crossover arrangement made of four Butterworth 
> stages (two as lowpass, another two as highpass). There is nothing 
> particularly good about the phase response. The feature of LR is that 
> the sum of the highpass and the lowpass channels makes for the perfect 
> allpass; although it is largely unimportant in practice.

You know, Vlad, you are the only one who picked up on carleeto's 
fundamental misconception. The rest of read "Linkwitz-Riley" and just 
assumed he _meant_ crossover. Good catch!

The important fearure od LR crossovers is that there is no cancellation 
of frequencies in the crossover region anywhere in a typical auditorium. 
Although a LY is allpass for voltage, it has a 3 dB power dip, which I 
think is more important -- as a defect -- in a typical living room.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

>>A Linkwitz-Riley crossover is an analog filter whose phase response can 
>>be only approximated by a digital model, and the approximation is
likely
>>to be poor unless the sampling frequency is up around 80 KHz or more.

I guess what I'm looking for is to design an equalizer that gracefully
transitions from an all-pass (EQ set to not do anything) to something
where the response is controller by the EQ parameters and I was under the
impression that an EQ based on LR filters would be the best one for the
job. Is there something better I could use? 

Thanks.

>A Linkwitz-Riley crossover is an analog filter whose phase response can 
>be only approximated by a digital model, and the approximation is likely

>to be poor unless the sampling frequency is up around 80 KHz or more.

Could you please explain further?