More > JRiver Media Center 29 for Windows
DSP Change Requests
BryanC:
Now that I don't have to convert Q->S I'm more likely to play around with custom parametric EQs. Could it be possible to add more than two and to rename them in the sidebar? I know this is somewhat possible with preset files, but it's way nicer just selecting/de-selecting them for AB.
mwillems:
--- Quote from: Matt on March 11, 2022, 12:43:36 pm ---Could you expound on this a bit? A new Low-pass is set to 12 dB/octave and 1 for Q. Are you saying it should be 12 dB/octave and .7071?
You can change the slope, but that doesn't change the Q.
Thanks.
--- End quote ---
So a first order butterworth (6db/octave) has a Q of .5, a 2nd order butterworth (12db/octave) has a Q of .7071. But higher order filters will have multiple poles and not all filters that have the same product Q have the same shape. I think the two poles of the 4th order butterworth are a Q of .541 and Q of 1.31, which make the product Q .7071. But if you change the poles you can wind up with the same product Q and a different slope instead.
To see more info, mattkhan linked a code example above from his beqdesigner program that shows how he modelled/calculated the Q factor for various pass filters: https://github.com/3ll3d00d/beqdesigner/blob/f2991ac3b78669ec237826ef18ca4f2afa885648/src/main/python/model/iir.py#L1208
This complexity was part of why I think mattkhan suggested offering presets for different filter shapes and orders. As it stands getting things right for higher order filters requires cascading several and setting the Q's just so.
Matt:
So what should we change the default to?
mattkhan:
--- Quote from: BryanC on March 11, 2022, 12:32:00 pm ---Aside, I was under the impression that Q is actually S in MC? https://wiki.jriver.com/index.php/Parametric_Equalizer#Q_or_S
--- End quote ---
Note that that only ever applied to shelf filters
mwillems:
--- Quote from: Matt on March 11, 2022, 01:08:32 pm ---So what should we change the default to?
--- End quote ---
I'd be interested to hear mattkhan's thoughts on this, but if we have to pick only one default (rather than defaults that shift by order), I think .7071 is the sanest default (i.e. least likely to result in surprising behavior).
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