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what is the width of the "q" parameter in Rockbox EQ?

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shady_slim:
I have Sansa Clip+ with RB v. 3.7.1 and Phonak PFEs with green and gray filters.

Knowing the characteristics of Phonak`s gray filters (the diagram is available on many sites) I would like to make it as linear (or rather sloping a bit down as the frequency goes up) using the advanced/graphical EQ. Actually - I have already done some EQing, but am not sure how accurate it was - just because I do not know how the "q" parameter works at different frequencies...

My guess is the width of the "q" changes with frequency - e.g. q=1 at 100 Hz means 100 Hz +/- 10Hz (so we can @ 100 Hz it is 20 Hz "wide"), while q=1 at 4000 Hz means 4000 Hz +/- 400 Hz (so we can say @ 4 kHz it is 800 Hz wide).

In the example above q=1 width is equal to 20% of the frequency it is applied at both for the frequency of 100 Hz and 4 kHz. So we could say it is a constant ratio parameter. Of course - it is just my assumption - it does not need to be constant and it may be calculated in a totally different way. But even if it is constant - the original question returns - how wide is it?

I will appreciate your help!

Multiplex:
I'm no expert but there's an article on Wikipedia about  Q http://en.wikipedia.org/wiki/Q_factor

shady_slim:

--- Quote from: Multiplex on February 26, 2011, 09:33:14 AM ---I'm no expert but there's an article on Wikipedia about  Q http://en.wikipedia.org/wiki/Q_factor

--- End quote ---

thanks a lot! I will try to "digest" it - it seems quite complex....

Datman:

--- Quote from: shady_slim on February 26, 2011, 07:54:25 AM ---Knowing the characteristics of Phonak`s gray filters (the diagram is available on many sites)
--- End quote ---
I haven't found it. Where is it?
Post Merge: February 28, 2011, 07:20:43 AM
--- Quote from: shady_slim on February 26, 2011, 07:54:25 AM ---My guess is the width of the "q" changes with frequency
e.g. q=1 at 100 Hz means 100 Hz +/- 10Hz (so we can @ 100 Hz it is 20 Hz "wide"),
while q=1 at 4000 Hz means 4000 Hz +/- 400 Hz (so we can say @ 4 kHz it is 800 Hz wide).
--- End quote ---
No. Q=f/B, where f=frequency and B=bandwidth, then B=f/Q. In your examples Q=5:
100+/-10Hz@-3dB => B=20Hz; Q=100/20=5
4000+/-400Hz@-3dB => B=800Hz; Q=4000/800=5.
Keep in mind that -3dB points are valid for a high gain or attenuation filter; if gain/attenuation is only a few dB you can't consider -3dB points...

E.g.: if you have a 4dB gain you have to consider the -3db of the 4dB over the unity-gain: 4dB=1.585, -3dB are 0.707 then 0.585*0.707=0.414; 1+0.414=3dB!

If you have a 2dB gain:
2dB=1.259 then 0.259*0.707=0.183; 1+0.183=1.46dB.

In few words it's similar to multiply dBs to 0.7:
4*0.7=2.8
2*0.7=1.4

shady_slim:

--- Quote from: Datman on February 28, 2011, 07:07:40 AM ---I haven't found it. Where is it?
--- End quote ---

e.g. here: http://sonusmobile.pl/data/include/cms/Phonak/Audeo_PFE_Bass_-_Frequency_Response_550.jpg


as you can see there are 3 peaks which need to be flattened:
1. @ about 2550 Hz which occupies fairly wide bandwidth and which needs to be reduced by some 8-9  dB (just by guessing I applied q = 0,7),
2. @ about 9600 Hz - very narrow, needs to be reduced by some 7-8 dB (similarly as above, I applied q = 5,5),
3. @ about 15 kHz - also narrow, needs to be reduced by some 4-5 dB (q = 5).

Sorry, but I am not sure if I understand your maths ???

You wrote Q = f/B

Assuming the first peak is @ 2550 Hz and it starts @ about 700 Hz I have calculated  B/2 = 2550 - 700 = 1850. this needs to be multiplied by 2  - i.e. B = 3700.

Does it mean Q = 2550/3700? It makes 0,69 - and this would means I was very close in my guessing  :D - provided you will confirm my calculation

Similarly f = 9600 Hz, B estimated at 2200 --> Q = 4,36

Am I right?

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