Re: Drawing an EQ curve
Re: Drawing an EQ curve
- Subject: Re: Drawing an EQ curve
- From: James Chandler Jr <email@hidden>
- Date: Wed, 3 Sep 2003 16:44:45 -0400
Hi Robert
A couple of years ago, somebody posted on the music-dsp list, a big
hairy long multi-line formula that purportedly plots a filter response.
Perhaps an "empirical" approach would give the most accurate freq
response? Accurately measure the actual freq response of the specific
imperfect EQ, rather than the theoretical response of a perfect EQ?
I like the idea of seeing the actual response rather than a theoretical
response.
You could feed an impulse into your EQ, then FFT the result, and plot
the FFT amplitude bins.
Alternately, feed a sine wave sweep thru the EQ, and plot the amplitude
of the returned sweep.
Since this does not have to be done repetitively, but only in response
to a screen refresh update or user interaction with the EQ UI, perhaps
such a brute force method wouldn't be completely crazy?
To avoid having to take your EQ offline in order to measure it, you
could make an internal "dummy" EQ object dedicated to calculating the
freq response display. When a draw is required, initialize the dummy EQ
object with the same coefficients as your actual on-line EQ object,
then pump a signal block thru the dummy EQ object and draw its freq
response? That ought not be exorbitantly expensive or slow.
James Chandler Jr.
On Wednesday, September 3, 2003, at 02:33 PM, Robert Grant wrote:
If I wanted to show a graphical representation of an EQ curve with
Freq, Gain and Q is there a cheap way to do it?
I've checked musicdsp.org but only found a detailed paper on
parametric EQing in general. Should I use the equations in that paper
or is there something simpler than can be a good approximation for
display purposes?
Thanks,
Robert.
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