Rockbox General > Rockbox General Discussion

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

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Chronon:
The bandwidth should correspond to the FWHM (full width at half maximum).  For a given peak, take the difference of the two frequencies where the height is half of the maximum.  Looking at the image you posted, 700 Hz looks much too low for the lower frequency at half-maximum.  Also, the frequency at the peak looks to be greater than 3000 Hz to me.

Datman:
It's very hard to equalize mechanical/acoustical resonances using an electrical filter. Earphones have to be chosen for the right sound. Strong resonances also produce distortion. It isn't simple, I know, but it is the same as for microphones: every singer chose his brand and model. No one thinks he could by a cheap microphone, then ask to the sound engineer to equalize it...

I've tried Shure E2 and E3 and Etymotic ER-4s (I've found good prices for new or used ones): ER4s are the best. Much better and cheaper are AKG K518LE foldable headphones, if you modify them with glass wool, resistor and capacitor. Now I use them outdoors with my Rockboxed Sansa Fuze.

cpu98:
I did flatten my etymotic mc5 with 2 shelving filters and 11(!) peaking filters.
Now I'm with a 20~20KHz-within-1dB earphone for mere 79 bucks.
I hear neglectable ringing, phase issue and group delay at sub bass and near ultrasonic region but it is comparable to a studio mointor.

I used electri-q equalizer(Bandwidth based) to get necessary values for filters.
(They are compatible with rockbox after you convert bw to q factor. Confirmed with a FFT analyzer)

First I made equalizer window transparent and let 'upside down response graph' below it and scaled the image.
And I fine-tuned equalizer so that those graph look like only one graph.
After correcting that get those value.
There is a q factor<-> bw converter (http://www.sengpielaudio.com/calculator-bandwidth.htm) you can use to determine q factor.

High range >= 8KHz needs care because filters become asymmetric.(Highs need broader q and lower cutoff than expected)

After that you measure that monster dap thing.
And say 'shit there is a line not a mountain on the monitor'

Extremely flat earphone is ultrabright as if it is made for dolphins so introduce gentle roll off after final correction.

Datman:
How did you get 11 peaking filters in Rockbox???

cpu98:
15band patch I used to equalize mine.

http://pastebin.com/vAXRd1zy

13band enabled + meier crossfeed eats 70+MHz on ipod video.
Luckily mine overclocks to 100MHz.
See #8668 if you use ipod video.

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