I found this value from REW website.
I understand about LR4 filter. If i want LR4 Lowpass, If applied double, it was LR4.
LowPass 90hz Q 0.707
LowPass 90hz Q 0.707
However, there is no information about BU1. Does anyone have any information about this? I was able to make a Bu1 filter with a fir filter in the Release, but I want to make the most of the functions in the Equalizer APO.
(Btw, The reason why I do this is that I have to make it manually because EQ APO does not apply even if I apply crossover LR, BU, etc. from REW and export it to Txt.)
I use EQ_APO for both XO and phase corrections, I may be able to answer a few of your questions.
As you've discovered, the default filters types are BW2 (BU2?), so to create LR4 = BW2 * BW2. I use this and measured and compared it to an ideal LR4 from RePhase. You can also check this using the "analysis" panel at the bottom of EQ_APO. Select the channel and look at the curve, you'll see 12dB/octave slope and flat response (Q=0.5) on the graph.
If you want arbitrary IIR digital filter forms, you'll need to calculate the coefficients. There are lots of tools like this one Digital IIR Calculator (or Octave) to do that and then use EQ_APO "custom filter like "Filter <n>: ON IIR Order <m> Coefficients <b0> <b1> ... <bm> <a0> <a1> ... <am>" The calculator I referenced provides you the [a,b] coefficient vectors in the auto code generator at the page bottom :
As you've discovered, the default filters types are BW2 (BU2?), so to create LR4 = BW2 * BW2. I use this and measured and compared it to an ideal LR4 from RePhase. You can also check this using the "analysis" panel at the bottom of EQ_APO. Select the channel and look at the curve, you'll see 12dB/octave slope and flat response (Q=0.5) on the graph.
If you want arbitrary IIR digital filter forms, you'll need to calculate the coefficients. There are lots of tools like this one Digital IIR Calculator (or Octave) to do that and then use EQ_APO "custom filter like "Filter <n>: ON IIR Order <m> Coefficients <b0> <b1> ... <bm> <a0> <a1> ... <am>" The calculator I referenced provides you the [a,b] coefficient vectors in the auto code generator at the page bottom :
REAL biquada[]={-0.931184116890369};
REAL biquadb[]={1};
REAL gain=29.063057968954443;
A first order filter only has a frequency parameter. Therefore there is only one possible alignment, and it doesn't make sense to talk about Butterwort etc. They are all the same.
That table is showing you the Q factor for each second order stage of the various filters listed. A filter of Nth order is constructed from N/2 second order filters when N is even, and (N-1)/2 second order filters plus a first order filter when N is odd. Like Henrik mentioned, there is only one type of first order filter. When a first order section is required, the table shows LP1 (low pass first order) / HP1 (high pass first order).
Side not: For all the filters listed (Butterworth and Linkwitz-Riley) the filter corner frequency and the corner frequency of any and all first and second order stages that make up that filter is the same. This is not always the case, but true for BUT and LR filters.
Side not: For all the filters listed (Butterworth and Linkwitz-Riley) the filter corner frequency and the corner frequency of any and all first and second order stages that make up that filter is the same. This is not always the case, but true for BUT and LR filters.
@Frabor I'm currently using an Asus Xonar AE 7.1, with Windows 10pro. The measurements are at Xonar AE Loopback