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Topic: Digital filters - quality value limits (Read 6420 times) previous topic - next topic
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Digital filters - quality value limits

Are there some "standards" for max/min of Q and bw values when used in EQ.

Would 0.001-100.000 for Q and 0.010 - 20.000 for BW be reasonable ranges?


Juha

Digital filters - quality value limits

Reply #1 –
I think 0.1 to 10 is pretty standard for Q.

BTW, Q is the width of the filter, with Q=1 having  bandwidth equal to the center frequency (so quite broad already). A Q of .001 would be so broad it would essentially just be a really complex way of doing a volume adjustment

Digital filters - quality value limits

Reply #2 –
Quote from: saratoga on
I think 0.1 to 10 is pretty standard for Q.
...


I was 'bout to select that range but, then checked the Electri-Q implementation which uses range 0.010-20.000.

As shown in the image (graph is for peak type filter), bw=20.000 corresponds Q=0.001:





In my EQ implementation, it's possible to switch the quality "type" to either Q or bw (or none (if not needed)).

In this implementation, the Notch type filter without given quality value corresponds a Notch filter with bw value set to ~0.048

(i.e. Q = 30.055) so if I select bw as min = 0.100 and max = 20.000 there's area left between those 2 type options that I can't control if needed.

I wouldn't want to set the Q/bw min/max by the filter type.


Juha

Digital filters - quality value limits

Reply #3 –
I'm not sure I understand what you mean?

Digital filters - quality value limits

Reply #5 –
I mean I don't understand what you're asking.  Did you still have a question?

Digital filters - quality value limits

Reply #6 –
Quote from: Juha on
Are there some "standards" for max/min of Q and bw values when used in EQ.


Look at commercial parametric equalizers implemented in the analog domain for guidance in that area.  The most recent implementations of real-world equalizers are parts of digital consoles.

Some software implementations are way beyond anything that anyone would actually use or need in real world recording, etc.

Quote
Would 0.001-100.000 for Q and 0.010 - 20.000 for BW be reasonable ranges?


Ne Plus Ultra, man.

Digital filters - quality value limits

Reply #7 –
In my experience, Q=0.01-40 are sufficient. There's no real reason to constrain it too badly - the main issue is numerical precision in the coefficients, especially at low frequencies.
ruxvilti'a

Digital filters - quality value limits

Reply #8 –
Above Q10 it's more of a phase effect than an EQ.
 

Digital filters - quality value limits

Reply #9 –
Yeah, the  phase shift can increase with Q (assuming minimum phase eq).
And it's preferable to use use smooth curves in your eq anyways.
Unless you use a linear phase eq, but I think you'd hear other artifacts with big  Q values.
Notice that  the Q value can have  different impact from a digital eq, to an other (not necessarily standard values are used).

Digital filters - quality value limits

Reply #10 –
High Q filters are almost necessary at high frequencies for precision, but I didn't find any use for Q=40 to be honest. Highest I've ever needed was 24 when equalizing headphones. Blame the darn s-plane for being so skewed.
ruxvilti'a