## Topic: 31 band Graphic EQ: Q factor values (Read 7809 times)previous topic - next topic

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• Juha
31 band Graphic EQ: Q factor values
##### 28 September, 2013, 03:05:42 PM
I'm preparing a 31 band Graphic EQ for Windows (Vista/7/8/?). It's gonna be based on biquad (peak) filters.

As being new (noob) with EQ design, I was wondering if the Q factor for each band "needs" to be equally set (lets say 4.318 for all 31 bands) and constant ?

There are lots of reading but, looks like I'm a bit lost there.

http://en.wikipedia.org/wiki/Equalization_(audio)
http://en.wikipedia.org/wiki/Filter_design#Digital_filters
http://www.rane.com/note101.html
http://www.sengpielaudio.com/calculator-bandwidth.htm
http://www.dummies.com/how-to/content/how-...or-an-audi.html
http://www.dafx.ca/proceedings/papers/p_037.pdf

Juha

• saratoga
31 band Graphic EQ: Q factor values
##### Reply #1 – 28 September, 2013, 04:03:55 PM
Generally the Q factor is a parameter that the user sets.  Its not usually constant per band, although it can be if the user wants each band to have the same fractional width.

31 band Graphic EQ: Q factor values
##### Reply #2 – 29 September, 2013, 06:19:12 AM
I'm preparing a 31 band Graphic EQ for Windows (Vista/7/8/?). It's gonna be based on biquad (peak) filters.

As being new (noob) with EQ design, I was wondering if the Q factor for each band "needs" to be equally set (lets say 4.318 for all 31 bands) and constant ?

There are lots of reading but, looks like I'm a bit lost there.

http://en.wikipedia.org/wiki/Equalization_(audio)
http://en.wikipedia.org/wiki/Filter_design#Digital_filters
http://www.rane.com/note101.html
http://www.sengpielaudio.com/calculator-bandwidth.htm
http://www.dummies.com/how-to/content/how-...or-an-audi.html
http://www.dafx.ca/proceedings/papers/p_037.pdf

Juha

Traditional Graphic equalizers with 30 +/- bands are always fixed constant Q.  Working with real world coils, capacitors, and resistors fixed parameters was the only practical way. This was almost always carried over into digital implementations of the same.

The basic idea was to approximate critical bands, which were not so well understood when the traditions started. The traditions carried over even when we understood critical bands better.

Graphic equalizers with smaller numbers of bands were mostly based on constant Q and constant bandwidth as well but there were some exceptions.

You can check this out with real world pro audio products. Leaders in this field include Behringer, Rane, Ashley, DBX, etc,

http://www.sweetwater.com/c468--Graphic_EQ

• Artcore87
Re: 31 band Graphic EQ: Q factor values
##### Reply #3 – 04 January, 2017, 02:47:53 AM
Traditional Graphic equalizers with 30 +/- bands are always fixed constant Q.  Working with real world coils, capacitors, and resistors fixed parameters was the only practical way. This was almost always carried over into digital implementations of the same.

Constant Q EQ's are great tools, far more useful than regular EQ's for making corrections (as opposed to mere wide-bandwidth tonal preferences... bass boost, mid cut, treble boost, stuff like that).  Parametric EQ's (as many bands as are needed) are the ultimate.  Nothing else matters but either the quality of the circuits and components, or for DSPs, the quality of the processing... bit depth/resolution/sample rate... the digital audio variables) in an equalizer.  Linear-phase EQ is mere marketing hype and offers no benefit, though i've played around with them.  Reading actual data however shows them to be worthless.  "minimum phase shift" is also a meaningless marketing term, since it applies to literally all equalizers by design.  complementary phase shift is another marketing term out there that's virtually meaningless.  For DSP, you want a high FFT... 65553 samples is what i use.  This determines the accuracy/resolution of the applied curve... how closely the digitally implemented curve matches up with the chosen settings.  Lower the FFT and you'll see the curve eventually become straight lines... it's literally just the resolution of the curve, it doesn't directly affect the fundamental quality of the audio signal, just the accuracy of the EQ effect.

Maybe someone will find this useful, cheers.

• saratoga
Re: 31 band Graphic EQ: Q factor values
##### Reply #4 – 04 January, 2017, 12:36:13 PM
Quote
While a traditional EQ's "Q" is not adjustable, it is only effectively constant when at full boost or full cut... key word effective.  A typical 1/3 octave EQ only has a 1/3 octave Q in practice when the adjustment is at full boost or full cut, as the boost or cut is lowered the actual Q becomes wider, this is simply a consequence of traditional designs, whether passive or active, or digital (most of which simply digitally mimic analog filters).

What?  Q is just the ratio the center frequency to the  bandwidth of an oscillator. It does not depend on amplitude.

Re: 31 band Graphic EQ: Q factor values
##### Reply #5 – 08 January, 2017, 10:32:40 PM
Traditional Graphic equalizers with 30 +/- bands are always fixed constant Q.  Working with real world coils, capacitors, and resistors fixed parameters was the only practical way. This was almost always carried over into digital implementations of the same.

I know this is an old thread, but I was searching for a constant Q dsp and found this thread.  The above information is incorrect,

What is incorrect is your interpretation of what I said. When I mentioned  "real world coils, capacitors, and resistors " I was obviously discussing the bandwidth of the actual filters that are inside the equalizer, not its external measured performance.  You must not know that when adjustments of height and depth of the peak or notch to be adjusted and allow low peaks and/or shallow dips, the effective bandwidth of the filter is naturally widened, and thus the Q is naturally broadened.

You further compounded this error by apparently suggesting that parametric eqs are somehow immune to this effect, which they are not.

For example, consider an equalizer of any kind that is set to create a 1 dB peak. The definition of Q is based on the points where the response fall 3 dB from the peak value, but this never happens since the peak is only 1 dB high.

The lesson is that comments like mine have a natural domain of validity which I stated in way that was relevant to the original context. Taking a comment out of its original context (in this case the actual individual filters) and putting it into a different context  (measured performance) to falsify it  is one of Schoepnhauer's 38 false tricks for winning every argument. This information is over 100 years old (originally written in German by someone who died in 1860 and translated to English in 1896) and is well known among well-educated people who are serious about the discussions that they are involved with.

Schopenhauer's 38 Stategems

Just to ensure that Schopenhauer's actual meaning is not missed, please let me point out that he was not trying to train people in methods for winning every argument by adding additional fallacies to the discussion.  He was trying to point out how to avoid getting hung up on ideas that may seem valid when looked at superficially, but fail to be reasonable when properly understood. Context is very important!

In the process of trying to make my correct statement appear false you made additional errors, one of which I just showed above. But the biggest error was taking my comment out of its natural context.

• andy_c
Re: 31 band Graphic EQ: Q factor values
##### Reply #6 – 16 January, 2017, 03:49:53 AM
Though I'm hesitant to dive into this thread, I thought I''d chime in anyway, just to try to clarify some things.  Unlike, say, bandpass filters, there is no single, commonly agreed upon definition for Q of PEQ filters.  I've summarized the mathematical relationships between a few of them here.