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Technical discussions related to Audio Signal Processing (digital effects, acoustics, noise reduction, musical signal processing, etc).

  

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Equalizers - sham...@gmail.com - Feb 27 10:49:33 2008

Hi Group,
Please tell can we connect filters in equalizers in parallel instead of
connecting them in cascade. Because we can achieve same effect in both the
case(|| or cascade) with adjusting gains of individual filters. Different gains
for parallel and cascade.





Re:Equalizers - Gene Goff - Feb 28 16:36:30 2008

Shamail,

Yes, you can connect equalizer filters in parallel instead of cascaded; however,
the boost/cut (gain/attenuation) filter responses will not be reciprocal as
viewed on a log-log scale (dB vs. log of frequency).  To get reciprocal
boost/cut responses with parallel filters, you must put the filter in a
feedforward path for a boost filter, but in a feedback path and subtract for a
cut filter.  I hope this helps.

Gene Goff
Ashly Audio, Inc.




Re: Re:Equalizers - Jeff Brower - Feb 29 7:23:05 2008

Gene-

> Yes, you can connect equalizer filters in parallel instead of cascaded;
> however, the boost/cut (gain/attenuation) filter responses will not be
> reciprocal as viewed on a log-log scale (dB vs. log of frequency).  To
> get reciprocal boost/cut responses with parallel filters, you must put
> the filter in a feedforward path for a boost filter, but in a feedback
> path and subtract for a cut filter.  I hope this helps.

What is the advantage of the parallel architecture?  Potentially faster
processing
time depending on the device architecture?  Is there an SNR or other signal
integrity
disadvantage in the add/sub stages?

-Jeff





Re: Equalizers - Gene Goff - Mar 2 8:45:00 2008

Jeff,

The advantage of the parallel architecture is that it will give you the same
filter combining response as an analog graphic EQ; that is, adjacent filters
will interact somewhat because you are *summing* filters rather than
multiplying.  Imagine that a given frequency, each filter's response can be
viewed as a vector having a magnitude and angle.  Adjacent filters will interact
by summing to a composite vector response.  This may seem bad, but people are
used to hearing most analog graphic EQ's which do this.

Cascaded filters on the other hand just multiply their transfer functions so
there is no filter interaction - the total response magnitude is simply the
product of the individual filter magnitudes.  This will give a response like
that of analog parametric EQ's.  Computationally, cascaded is a little more
efficient than parallel filters (because the parallel cut {feedback} filters
have to be handled differently than the boost {feedforward} filters), but could
be noisier because any recursive truncation noise can only get worse as you add
more cascaded stages.  For summing parallel filters, any recursive truncation
noise will add basically geometrically so there is some "cancellation"
of noise.

In the end, the main reason to use parallel filters is to get something that
behaves like a conventional analog graphic EQ and use cascaded filters to get
something that behaves like a conventional parametric EQ.

Gene




Re: Re: Equalizers - Jeff Brower - Mar 3 6:48:05 2008

Gene-

> The advantage of the parallel architecture is that it will give you the
same filter combining response as an analog
> graphic EQ; that is, adjacent filters will interact somewhat because you
are *summing* filters rather than
> multiplying.  Imagine that a given frequency, each filter's response can be
viewed as a vector having a magnitude and
> angle.  Adjacent filters will interact by summing to a composite vector
response.  This may seem bad, but people are
> used to hearing most analog graphic EQ's which do this.
>
> Cascaded filters on the other hand just multiply their transfer functions
so there is no filter interaction - the
> total response magnitude is simply the product of the individual filter
magnitudes.  This will give a response like
> that of analog parametric EQ's.  Computationally, cascaded is a little more
efficient than parallel filters (because
> the parallel cut {feedback} filters have to be handled differently than the
boost {feedforward} filters), but could
> be
> noisier because any recursive truncation noise can only get worse as you
add more cascaded stages.  For summing
> parallel filters, any recursive truncation noise will add basically
geometrically so there is some "cancellation" of
> noise.
>
> In the end, the main reason to use parallel filters is to get something
that behaves like a conventional analog
> graphic EQ and use cascaded filters to get something that behaves like a
conventional parametric EQ.

Thanks very much for that explanation.  We did a TI 5510 based stereo audio
equalizer implementation in 2005-2006 for
a customer who wanted to match "analog parametric EQ" performance. 
Accurate and stable parametric filter frequency
responses were required down to 10 Hz using a 48 kHz sampling rate, so we ended
up with 64-bit precision in our IIR
implementation of the parametric filters.  After that experience I thought I
knew something about audio equalizers,
but clearly it's a deep subject, one you appear to have mastered.  Thanks
again.

-Jeff





Re: Equalizers - sham...@gmail.com - Mar 28 15:47:40 2008

Hi Group
I am having say 10 filters for equalizer and I want to process audio through
these. How should I do it ?

1) First convolve all the filters nums and dens coeffs and find a single
filter's Num and Den and then process audio through this single filter or 

2) process the audio through 1st filter get resultant audio and then process
this audio through 2nd filter and so on.

Please guide me what to follow.
I think 2nd approach is batter because convolving all the filters coefficients
may make resultant filter unstable. I am I right?
also tell me what is professional approach.
Tx
Shamail

Hi Group,
>Please tell can we connect filters in equalizers in parallel instead of
connecting them in cascade. Because we can achieve same effect in both the
case(|| or cascade) with adjusting gains of individual filters. Different gains
for parallel and cascade.






Re: Re: Equalizers - Prajakt Kulkarni - Apr 2 15:24:51 2008

I am assuming this was for audio application? Why would you require a
reponse down to 10 Hz? Human ears cannot hear anything below 20 Hz.
Prajakt.
-----------------
Thanks very much for that explanation. We did a TI 5510 based stereo audio
equalizer implementation in 2005-2006 for 
a customer who wanted to match "analog parametric EQ" performance.
Accurate and stable parametric filter frequency 
responses were required down to 10 Hz using a 48 kHz sampling rate, so we ended
up with 64-bit precision in our IIR 
implementation of the parametric filters. After that experience I thought I knew
something about audio equalizers, 
but clearly it's a deep subject, one you appear to have mastered. Thanks again.


-Jeff






Re: Re: Equalizers - Jeff Brower - Apr 2 15:25:06 2008

Prajakt-

> I am assuming this was for audio application? Why would you require a
reponse
> down to 10 Hz? Human ears cannot hear anything below 20 Hz.

Yes I agree, but nevertheless that was the spec we were given.  I put it in the
same
category as 24-bit A/D converters -- you can't hear the difference between 20
and 24
bit in a circuit designed for a consumer audio product, but there is a
marketing
aspect to it.

-Jeff

> -----------------
> Thanks very much for that explanation. We did a TI 5510 based stereo audio
equalizer implementation in 2005-2006 for
> a customer who wanted to match "analog parametric EQ"
performance. Accurate and stable parametric filter frequency
> responses were required down to 10 Hz using a 48 kHz sampling rate, so we
ended up with 64-bit precision in our IIR
> implementation of the parametric filters. After that experience I thought I
knew something about audio equalizers,
> but clearly it's a deep subject, one you appear to have mastered. Thanks
again.
> 
> -Jeff