Re: Drawing an EQ curve
Re: Drawing an EQ curve
- Subject: Re: Drawing an EQ curve
- From: James Chandler Jr <email@hidden>
- Date: Thu, 4 Sep 2003 10:43:41 -0400
On Thursday, September 4, 2003, at 02:53 AM, Urs Heckmann wrote:
In that case, you could make a "hidden", minimal mixer channel that you
- set Settings of currently edited channel
- reset();
- feed IR (i.e. only cos part of all the bins you want to display,
zero padded to end of buffer)
<snip>
this looks quite expensive, but an asynchronus calculation might be
sufficient (limitted to 5 times per second or so)
Yes it would have to be a separate offline test module, because most
EQ's have memory, and would glitch if taken offline internally and
rerouted long enough to do a test.
When Robert asked the question, I thought he was talking about a plugin
of his own, where he has access to the innards. Inside a plugin, it
would be pretty cheap to keep a duplicate test EQ object, and very fast
(considering all the other stuff the computer is doing) to occasionally
test the freq response for screen display. IIR EQ's are typically very
efficient, and a test loop would be fast and easy inside a plugin.
Just yesterday on music-dsp, Roman Katzer posted a link to a good,
appropriate paper about freq response measurement--
http://iem.at/~noisternig/iem/bt2003/literature/Mueller_sweep
Another approach that might be made to work, not requiring a dummy
offline EQ (one of the methods described in that paper)...
As long as the EQ is passing signal, one could FFT both the input and
output of the "black box" EQ, and derive the frequency response from
the difference.
But if the "black box" EQ is sitting idle, when playback is not
happening, it might get trickier figuring out the right way to test it.
James Chandler Jr.
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