IIR audio filterbank

I am looking for a way to design an audio IIR filterbank. I need to
split an audio signal into roughly 1/3 octave bands with 6th-order or
8th-order IIR bandpass filters and then sum them back together again
with a ripple of +/- 1 dB. I can do a "seat-of-the-pants" design that
works well until I approach Nyquist where it kind of falls apart. I
have very limited MIPs so I can't do anything very fancy. Any
pointers?


Bob

Robert Adams wrote:

> I am looking for a way to design an audio IIR filterbank. I need to
> split an audio signal into roughly 1/3 octave bands with 6th-order or
> 8th-order IIR bandpass filters and then sum them back together again
> with a ripple of +/- 1 dB. I can do a "seat-of-the-pants" design that
> works well until I approach Nyquist where it kind of falls apart. I
> have very limited MIPs so I can't do anything very fancy. Any
> pointers?

Constant Q transform?


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

On Oct 12, 9:37=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> Robert Adams wrote:
> > I am looking for a way to design an audio IIR filterbank. I need to
> > split an audio signal into roughly 1/3 octave bands with 6th-order or
> > 8th-order IIR bandpass filters and then sum them back together again
> > with a ripple of +/- 1 dB. I can do a "seat-of-the-pants" design that
> > works well until I approach Nyquist where it kind of falls apart. I
> > have very limited MIPs so I can't do anything very fancy. Any
> > pointers?
>
> Constant Q transform?
>
> Vladimir Vassilevsky
> DSP and Mixed Signal Design Consultanthttp://www.abvolt.com

Sounds right, but it needs to sum directly to create an approximation
of the input; that is, I can't afford a "synthesis filterbank".

Robert Adams wrote:

> On Oct 12, 9:37 pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> 
>>Robert Adams wrote:
>>
>>>I am looking for a way to design an audio IIR filterbank. I need to
>>>split an audio signal into roughly 1/3 octave bands with 6th-order or
>>>8th-order IIR bandpass filters and then sum them back together again
>>>with a ripple of +/- 1 dB. I can do a "seat-of-the-pants" design that
>>>works well until I approach Nyquist where it kind of falls apart. I
>>>have very limited MIPs so I can't do anything very fancy. Any
>>>pointers?
>>
>>Constant Q transform?
>>
> Sounds right, but it needs to sum directly to create an approximation
> of the input; that is, I can't afford a "synthesis filterbank".

What is the application ? I.e. if this is supposed to be a graphic 
equalizer, there are many more efficient ways to accomplish that.


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

Robert Adams wrote:

> On Oct 12, 9:37 pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> 
>>Robert Adams wrote:
>>
>>>I am looking for a way to design an audio IIR filterbank. I need to
>>>split an audio signal into roughly 1/3 octave bands with 6th-order or
>>>8th-order IIR bandpass filters and then sum them back together again
>>>with a ripple of +/- 1 dB. I can do a "seat-of-the-pants" design that
>>>works well until I approach Nyquist where it kind of falls apart. I
>>>have very limited MIPs so I can't do anything very fancy. Any
>>>pointers?
>>
>>Constant Q transform?

> Sounds right, but it needs to sum directly to create an approximation
> of the input; that is, I can't afford a "synthesis filterbank".

P.S. You do know of Linkwitz-Riley filters, do you?

VLV

On Oct 12, 11:59=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>
> P.S. You do know of Linkwitz-Riley filters, do you?
>


you might find both Bob's name and Siegfried Linkwitz listed here:
http://www.aes.org/awards/ .

(i think Bob knows about L-R).

r b-j

On Oct 13, 12:10=A0am, robert bristow-johnson
<r...@audioimagination.com> wrote:
> On Oct 12, 11:59=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>
>
>
> > P.S. You do know of Linkwitz-Riley filters, do you?
>
> you might find both Bob's name and Siegfried Linkwitz listed here:http://=
www.aes.org/awards/.
>

fuck!  i can't believe it.  i *knew* i would see Bob's name on the
list because i know a couple of times he got AES awards.  but i cannot
believe that Linkwitz's name is not on the list.  unbelievable!  the
AES never awarded Linkwitz and Riley a fellowship or, at least, a
publication award???!!

can't figger that one out.

r b-j

On Oct 13, 12:12=A0am, robert bristow-johnson
<r...@audioimagination.com> wrote:
> On Oct 13, 12:10=A0am, robert bristow-johnson
>
> <r...@audioimagination.com> wrote:
> > On Oct 12, 11:59=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>
> > > P.S. You do know of Linkwitz-Riley filters, do you?
>
> > you might find both Bob's name and Siegfried Linkwitz listed here:http:=
//www.aes.org/awards/.
>
> fuck! =A0i can't believe it. =A0i *knew* i would see Bob's name on the
> list because i know a couple of times he got AES awards. =A0but i cannot
> believe that Linkwitz's name is not on the list. =A0unbelievable! =A0the
> AES never awarded Linkwitz and Riley a fellowship or, at least, a
> publication award???!!
>
> can't figger that one out.
>
> r b-j

Yes I know about L-R, but I am looking for something with > 30
bandpass filters, not sure L-R can be extended to that case?

Bob

On Oct 13, 4:37=A0am, Robert Adams <robert.ad...@analog.com> wrote:
> On Oct 13, 12:12=A0am, robert bristow-johnson
>
>
>
>
>
> <r...@audioimagination.com> wrote:
> > On Oct 13, 12:10=A0am, robert bristow-johnson
>
> > <r...@audioimagination.com> wrote:
> > > On Oct 12, 11:59=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrot=
e:
>
> > > > P.S. You do know of Linkwitz-Riley filters, do you?
>
> > > you might find both Bob's name and Siegfried Linkwitz listed here:htt=
p://www.aes.org/awards/.
>
> > fuck! =A0i can't believe it. =A0i *knew* i would see Bob's name on the
> > list because i know a couple of times he got AES awards. =A0but i canno=
t
> > believe that Linkwitz's name is not on the list. =A0unbelievable! =A0th=
e
> > AES never awarded Linkwitz and Riley a fellowship or, at least, a
> > publication award???!!
>
> > can't figger that one out.
>
> > r b-j
>
> Yes I know about L-R, but I am looking for something with > 30
> bandpass filters, not sure L-R can be extended to that case?
>
> Bob- Hide quoted text -
>
> - Show quoted text -

Application is a bit like a graphic EQ but I need to measure the
energy in each band with pretty good selectivity, and my MIPs are so
limited that I wanted to use the same filters for energy estimation as
for the graphic EQ, which means I need to use the "parallel-sum" form
of graphic EQ instead of the "cascade-of-peaking-filters" form.
Unfortunately this means you get all the messy phase effects when each
filter crosses over with its upper and lower neighbors.

Bob

On Oct 13, 4:42=A0am, Robert Adams <robert.ad...@analog.com> wrote:
...
> Application is a bit like a graphic EQ but I need to measure the
> energy in each band with pretty good selectivity, and my MIPs are so
> limited that I wanted to use the same filters for energy estimation as
> for the graphic EQ, which means I need to use the "parallel-sum" form
> of graphic EQ instead of the "cascade-of-peaking-filters" form.
> Unfortunately this means you get all the messy phase effects when each
> filter crosses over with its upper and lower neighbors.

Bob, i might have mentioned this to you one of those times we were
having lunch at the Green Papaya, but an idea for a paper that i had
but have done little about is an automated way of turning that
"cascade-of-peaking-filters" form into an equivalent parallel-sum
form:

a graphic EQ with 3 sliders per octave, and a pretty constant 1/3
octave bandwidth on each peaking filter.  but then apply
(automagically) the Heaviside partial fraction expansion to this thing
and come out with a bunch of parallel 2nd-order filters (each with 2
coefs in the numerator) and one feedforward path of the dry input.  i
sorta think this would be a good thing for an EE grad student to do.

the reason i liked it this way is because the double-precision word
that results from every parallel filter need not be truncated, but
summed in a big accumulator with that result truncated (and noise-
shaped).  being parallel, it might be cleaner than 25 peaking-EQs in
series, each quantizing its output.  but being the same transfer
function as the 25 peaking-EQs in a row, it wouldn't have the phase
cancellation problem of the side skirts of adjacent bands typical in
the parallel context.

r b-j