Generic/DCX2496 shelving filters center frequency - Home Theater Forum and Systems - HomeTheaterShack.com

Old 05-13-13, 01:20 PM Thread Starter
Shackster
Jonas Thedering (jt)

Join Date: Apr 2007
Posts: 42
Generic/DCX2496 shelving filters center frequency

Hello,
I'm the developer of Equalizer APO and I'm currently working on support for filter types other than peaking filters. I would like to support all filters types the "Generic" equalizer supports and stumbled over the LS/HS 6 dB/12 dB filters (which seem to be copied from the DCX2496). These look like regular shelving filters but the frequency entered into REW is not the center frequency, more like the cutoff frequency of a lowpass/highpass filter. I could not figure out what the exact meaning of the frequency is. To implement the filter as a biquad I need to know the center frequency of the shelving filter.

Does anybody know the meaning of the frequency or better, how to calculate the center frequency from it? Here are some sample values I read from Room EQ Wizard for the LS 12 dB filter with frequency 10000 Hz:

 Gain (dB) -2,5 -5 -7,5 -10 -12,5 -15 -17,5 -20 Center frequency (Hz) 10741 11546 12405 13333 14330 15395 16548 17777

Last edited by Matrix86; 05-13-13 at 01:22 PM. Reason: Added link to EQ APO thread
Matrix86 is offline

Old 05-13-13, 03:22 PM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,306
Re: Generic/DCX2496 shelving filters center frequency

To correspond to the definitions used by the DCX the frequency needs to vary with square root of gain (or square root of that for the 12 dB filters). This code fragment should convey the gist:
Code:
```            case LS6:
gainFactor = Math.pow(10.0, Math.abs(gain)/40.0);
omega = fc*gainFactor *norm;
break;

case HS6:
gainFactor = Math.pow(10.0, Math.abs(gain)/40.0);
omega = fc*norm/gainFactor ;
break;

case LS12:
gainFactor = Math.pow(10.0, Math.abs(gain)/80.0);
omega = fc*gainFactor *norm;
break;

case HS12:
gainFactor = Math.pow(10.0, Math.abs(gain)/80.0);
omega = fc*norm/gainFactor ;
break;```
The shelf slope is 0.5 for the 6 dB filters and 1.0 for the 12 dB.
JohnM is offline
Old 05-14-13, 02:26 PM Thread Starter
Shackster
Jonas Thedering (jt)

Join Date: Apr 2007
Posts: 42
Re: Generic/DCX2496 shelving filters center frequency

Thank you very much! Your answer, especially the code, was really helpful. This thread can be closed.
Matrix86 is offline

 Bookmarks

 Tags center , filters , frequency , generic or dcx2496 , shelving

Message:
Options

## Register Now

Random Question
Random Question #2

User Name:
OR

## Log-in

 User Name Password Remember Me?
Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.