REW and BFD FBQ2496

[Dwight Angus]

I finally received FBQ2496 and re ran REW to make sure I was getting the same results. I then loaded the BFD manually with the filters in PEQ mode. I removed bypass mode and PEQ mode so the bfd indicates "RUN". I then ran REW engaging bfd to see the results expecting to see a graph that looks like the optimzed graph in REW with spl close to the target line. The first graph is the optimized graph before bfd filters applied and graph 2 is after bfd filters applied.As you can see the graphs are completely different. I reloaded the filters several times with the same results.

Can anyone tell me what the problem is?

cheers
Dwight

[thsmith]

Dwight, I am by no means a REW expert but it looks like you are running a lot of filters. Not sure if that helps or not as I do not have the same BFD as you.

I did the same thing when I setup my 1124P the last couple of days.

Quote below from weverb that provided a lot of help.

Obviously read the whole thread, but read this section a few times:

http://www.hometheatershack.com/foru...html#post55656


Tips for those who use REW’s auto-equalizing function

[Dwight Angus]

Thanks Tracy

Yeah I loaded the filters that REW recommended when optimizing the graph. My latest version has reduced the # of filters to 4 due to the graph results keep changing. Not sure if this is too many of not. The problem is probably due to me changing the avr volume.

I will check out the thread you mentioned

cheers
Dwight

[thsmith]

You need to do this before applying filters.

Optimize REW filters for response smoothing...
First, REW calibrate for the standard 75 dB Target in the Settings panel. Take your measurement sweep, then adjust your viewing window for a 20-130 dB setting, using the Graph Limits box (top right of screen), so that your response curve doesn’t look so scary. (NOTE: This is mainly for your benefit – REW will recommend its filters irrespective of widow resolution.)

Next, re-adjust the Target Level to a good midway point between your response peaks and depressions - or if your particular curve permits, align the Target to where it most closely tracks the bulk of your response curve.

Under Trace Adjustments, set the Smoothing option to 1/3-octave, which will help induce REW to focus more on the most serious problems instead of the minor ones. Then under Filter Tasks, limit the Find Peaks range to a bit below your crossover point. The response you’re seeing close to the crossover frequency is most likely duplicated by the mains, so it’s to no effect to equalize up there. (Of course, this needs to be verified by comparing graphs for sub only, mains only, and both together.)

Next run the Find Peaks, Assign Filters, Optimize PK Gain, and Adjust PK Gain functions.

[Dwight Angus]

Thanks Tracy

Good input

I will rerun later today and post some graphs

[Wayne A. Pflughaupt]

I removed bypass mode and PEQ mode so the bfd indicates "RUN". I then ran REW engaging bfd to see the results expecting to see a graph that looks like the optimzed graph in REW with spl close to the target line. The first graph is the optimized graph before bfd filters applied and graph 2 is after bfd filters applied.As you can see the graphs are completely different.

If I understand, you expected the response in the bottom graph to look like the dotted line in the top graph?

Keep in mind that the dotted line in the first graph is merely a prediction. You might want to try taking readings adding one filter at a time and adjusting them as needed. Better yet, use REW's RTA function and you can tweak the filters in real time.

Regards,
Wayne

[DrWho]

Dwight Angus wrote:

Can anyone tell me what the problem is?

Well that would be one tell tale sign of EQ being applied to frequency aberrations that aren't minimum phase...I don't think mangling filters to achieve a flat response is going to be the best sounding solution either.

[Dwight Angus]

Thanks Wayne
I have not yet used the rta function but I will give it a go.

I have another REW question. When in the measure screen and I check levels it tells me the levels are too low ie in the 40 db range. Not sure what this is about when I have already calibrated the sbl meter to 75 db and all VU levels are within range. If I increase levels then I clip. What am I doing wrong?

cheers
Dwight

[brucek]

Keep in mind that the Check Levels routine in the Measurement screen and the Check Levels routine in the Settings screen use different values to generate the pink noise level setup test signal.

The Check Levels routine in the the Settings screen uses the fact that you have the Check/Set levels with Subwoofer pull-down selected to generate its test noise (this a band limited signal with a low and high cut of 30Hz - 80Hz).

REW double checks and verifys that the end frequency of the sweep that you have selected in the Measurement panel roughly matches the test signal setting (for sanity), so its Check Level routine uses the end frequency as the test pink noise hi-limit cutoff, resulting sometimes in a low or high warning.

brucek

[Dwight Angus]

Brucek

Thanks for the input.

In the measurement screen check levels I am usually too low by ~35db and when I attempt to increase levels it remains low. REW does allow me to continue measuring when I ignore the low levels message but does that create an inaccurate or distorted response and if so is there something else I should be doing to increase these low levels?

cheers
Dwight

[brucek]

when I attempt to increase levels it remains low.

How do you increase levels? What are you adjusting?

Also, what is your start and end frequency when this occurs - 0Hz-200Hz?

brucek

[Dwight Angus]

Brucek

You are right it was the start/end frequency points that were incorrect. I have set them to show 0hz to 200hz. Measurement check levels are working .

Thanks
Dwight