INTERACT FORUM

More => Old Versions => Media Center 17 => Topic started by: luckyluke on June 30, 2012, 05:01:51 am

Title: Equalizer parameters
Post by: luckyluke on June 30, 2012, 05:01:51 am

Does anybody could explain High/low shelf filters parameters ? Especially Bandwith...

I have eletrostatic panels and I need to set-up some high shelf filters from 20hz up-to 400 hz with a theorical slop of 3db per octave, how can I calculate Bandwith ?

Thanks !

Title: Re: Equalizer parameters
Post by: Scolex on June 30, 2012, 12:35:34 pm

Bandwidth (Q) is just how steep the slope is as it moves away from the center frequency.
For example a Q of 1.4 has a bandwidth of one octave so if you set a 6db boost at 30Hz the boost would be gone by the time in got to 15Hz on the low side and 60Hz on the high side.
Just in case you don't know what an octave is it is the doubling of a frequency.
(20-40, 40-80, 80-160, 160-320, 320-640, 640-1280, 1280-2560, 2560-5120, 5120-10240, 10240-20480)
This might help.
http://www.sengpielaudio.com/calculator-bandwidth.htm

Title: Re: Equalizer parameters
Post by: luckyluke on July 03, 2012, 02:23:34 pm

Thank you Scolex,

I've set-up a high-shelf with 20Hz frequency 0.18 Q factor (5 octave  bandwith from 20 to 640 Hz) and -15 dB slope and it seems to sound fine;

I suppose that for shelving filter "Frequency" stands for cut-off frequency not center frequency... Am I right ?

Title: Re: Equalizer parameters
Post by: Scolex on July 03, 2012, 03:34:01 pm

Quote from: luckyluke on July 03, 2012, 02:23:34 pm

Thank you Scolex,
I suppose that for shelving filter "Frequency" stands for cut-off frequency not center frequency... Am I right ?

Yes you are correct.
I think of them as being like a crossover only they attenuate consistently above/below the frequency instead of a continuous downward slope.
Make sense?

Title: Re: Equalizer parameters
Post by: dean70 on July 03, 2012, 08:43:34 pm

I could not get a wide shelf filter to show properly in the RTA - it appeared as though it "shelved" at about 2 octaves (tested using the tone function in DSP Room Correction).

Title: Re: Equalizer parameters
Post by: luckyluke on July 04, 2012, 04:17:12 pm

Thanks to you Dean70 ! It's a really good idea to test equlization using tone (pink noise ?) and analyser view; Even if it could have been more accurate, it gives some ideas about the real effect of filters...

As a result, shelving filters seems to work like that :

Frequency = central frequency (not like crossover cut-off frequency as I was wondering before)
Bandwidth = not used ( constant filter slope )
Gain = total gain/attenuation between lowest and highest frequency

Actually filter slope is 3 dB per octave, so you could adjust the real band width by setting the correct gain value; For instance a gain value of 12 dB will give a four octave band width

Example : F= 140, B=NA, G=-12 => sheving filters with 3 dB slope from 35 Hz to 560 hz, -12db after 560 hz

Could anyone from dev team confirm or not ?
 

Title: Re: Equalizer parameters
Post by: dean70 on July 04, 2012, 05:52:31 pm

That explains it then! I had a -6db high shelf from 4k & wanted in down -6db by 8k for movies and a second one for music from 2k -6db down by 16k, but couldnt get a wide enough slope - want to create X curve eqs for both movies & music).

Might be better to create a target curve as part of DRC & use to convolution engine to create the response (which brings a whole new set of challenges).