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lovingdvd 05-31-15 11:27 AM

Tweaking filters after an initial filter set
 

I've long wonder about this and was once again trying to figure out what the right way is to tweak a filter set after an initial filter set is sent. I am using the BFD 1124.

Here's what I do now:

1. Take measure
2. Go to EQ window
3. Click Set Target Level
4. Click Send Filter Settings to Equalizer

Question 1: Is the above right so far?

5. Take new measure and review results.

OK at this point let's say I wanted to tweak something that REW didn't attempt to adjust or didn't adjust enough. I go back to the EQ window, but when I click the EQ Filters button at the top, all the filters are gone - its reset.

So at this point it seems I cannot tweak anything, because REW has lost track of what is already set in the BFD on that channel. And I guess retrieving the filters from the BFD is not an option because that is grayed out in REW (I'm using the Midi Uno if that matters).

What I'd like to do is tell REW "OK that was a good start but let's tweak this and retry" but not sure how to do that.

I have tried saving the Filters to a file after clicking Send Filter Settings to Equalizer, and then the next time opening that file so REW has a starting point. Is that on the right track? If so, couldn't REW just remember the last filters it did? It would save a lot of steps and help me when I forget to save the filters.

OK so let's say I do remember to save the filters. After step 5 I then:

6. Open saved filters in EQ window
7. Add a Manual filter to address a small dip or peak.
8. Click on Optimize Gains, Qs, and Frequencies - not much changes (is this right? if not when are you supposed to use this?)
9. Send filters back to BFD.
10. Remeasure latest results. At this point I notice that the large peak I have at 30 Hz, which was corrected by the initial REW EQ filters, is back like the peak wasn't treated, even though all the same filters were sent back to the BDF. The lights on the BFD seem to indicate the right number of filters are set.

Confused. Thank you.

JohnM 05-31-15 11:40 AM

Re: Tweaking filters after an initial filter set
 

I guess there is a 3b "Match response to target" step, otherwise 1-4 look fine.

Filter sets are associated with specific measurements, so if you go back to the measurement you made when you set the filters you should see them there. Making a new measurement means starting with the filter set empty. Saving and loading filters from file is the only way to transfer a set of filters between measurements, but it wouldn't usually be a good thing to do with a post-EQ measurement as the features REW was trying to correct first time around (e.g. your 30 Hz peak) won't be present in the post-EQ measurement, so re-optimising will remove the corrections that were being applied for those features. Probably better off going back to the original measurement and adding an extra filter there.

lovingdvd 05-31-15 12:26 PM

Re: Tweaking filters after an initial filter set
 

Quote:

JohnM wrote: (Post 1219346)
I guess there is a 3b "Match response to target" step, otherwise 1-4 look fine.

Filter sets are associated with specific measurements, so if you go back to the measurement you made when you set the filters you should see them there. Making a new measurement means starting with the filter set empty. Saving and loading filters from file is the only way to transfer a set of filters between measurements, but it wouldn't usually be a good thing to do with a post-EQ measurement as the features REW was trying to correct first time around (e.g. your 30 Hz peak) won't be present in the post-EQ measurement, so re-optimising will remove the corrections that were being applied for those features. Probably better off going back to the original measurement and adding an extra filter there.

3b. Yes meant to add that.

I'm a little confused about the process. Let's say I take measurement 1 as a baseline and blank filter set in BFD. I go to EQ window and go through the above steps, sending the filters to the BFD.

OK so now I want to see how the filters did. I take a new measure (right?). Now on measure 2 I see a lot of improvement but a few tweaks still needed.

You say "Probably better off going back to the original measurement and adding an extra filter there". So then I click on Measure 1 and when I go back to EQ I will see the filters that are in the BFD post measurement 1? Add manual filter(s) there but do NOT click on any of the "Optimize" options. Upload that back to the BFD and take a new measure, and at this point the new measure will give me the baseline combined with the original filters REW set plus my manual tweaks.

Do I have this right?

JohnM 05-31-15 01:32 PM

Re: Tweaking filters after an initial filter set
 

You can re-optimise the original set after you add your manual filters, the important thing is not to try optimising an existing filter set against a measurement that already has filtering applied to it.

lovingdvd 05-31-15 08:21 PM

Re: Tweaking filters after an initial filter set
 

Quote:

JohnM wrote: (Post 1219466)
You can re-optimise the original set after you add your manual filters, the important thing is not to try optimising an existing filter set against a measurement that already has filtering applied to it.

Thanks. The part I was not understanding was that the EQ window was relative to the selected measure. So I would take measure 1, apply filters, then look at measure 2, and go back to filters to try tweaking further - but since measure 2 was highlighted when I went back into the EQ window all the filters were reset, of course. If I highlight measure 1 and then go to the EQ window then I can tweak and reapply new filters. So I am all set there.

Two questions on the subject of filters... When I first use REW and measure and set filters and apply them, when I do the 2nd measurement the measure is the same as the first, even though the filters were applied in the BFD. I have to go through the same steps a second time before the filters take effect. Have you seen anything like this?

Here's an example:
Start fresh with BFD channel 1, no filters
Using house curve 20: 4.0, 80 0.0
Disconnect Front Left speaker so only sub will output sound.
Output on Soundcard tab set to HD Audio HDMI out 1
Run Check Levels from Preferences Sound Card screen, with use Subwoofer to set/check levels selected.
Adjust sub gain to 75 dB
Measure with start 0, end 300 Hz, level -12, length 512k, sweeps 2
Headroom 8.6 dB green shown
Measurement is labeled "Baseline". Large peak (about +20 dB at 30 Hz).
With Baseline selected (only measure at this point), click on EQ button to open EQ window
Click on Set Target Level, it sets it to 67.9.
Click Match Response to Target.
Predictive curve shows peak at 30 Hz will be gone.
Send updated filters to BFD. Completes successfully.

So far would you say those steps all seem accurate and I haven't skipped anything?

OK so to continue...
Switch back to Measure screen and remeasure. Results labeled Calibrated 1.
Large peak at 30 Hz was unchanged - why? BFD on channel 1 shows all 12 filters are set (12 LEDs)
Select Baseline measure. Return to EQ window.
Click Reset Filters for current measurement. Sent to BFD. Verified all 12 LEDs for filters are now off.
Take a new measure, labeled as Baseline Try 2
Go to EQ window. Set Target Level. It chooses 68.
Choose Match Response to Target.
Send to BFD. Verify 12 LEDs are lit for 12 filters (I have it set to try and get within 1dB).
THIS TIME IT WORKS. Results labeled as Calibrated 2.

Any idea why filters didn't "take" the first time? I seem to have recall seeing this before - like each time I start a new REW session and try to start from scratch. Maybe it is the way I am resetting the BFD channel to begin with? Before the first measure I go to the EQ window and say Reset Filters and send them to the BFD just to black them out. So that I am taking the first measure without any calibration applies by the BFD.


Question 2:
After auto filters were applied the results were very good. I had a -4 dB dip at 21.5 Hz compared to 20 Hz and 25 Hz. Why didn't REW attempt to fix this? I have the filter settings at their defaults so its allowed to apply an individual max boost of 9 dB (the default for overall boost seems to be 0 dB, so how could default for individual be 9 dB?) but it didn't attempt to fix it.

Thanks!

JohnM 06-01-15 04:31 PM

Re: Tweaking filters after an initial filter set
 

Quote:

lovingdvd wrote: (Post 1219770)
I have to go through the same steps a second time before the filters take effect. Have you seen anything like this?

No. Perhaps the midi interface isn't working reliably? Could try just sending the filters again, and view the filter settings on the BFD to see what has been transferred.

Quote:

After auto filters were applied the results were very good. I had a -4 dB dip at 21.5 Hz compared to 20 Hz and 25 Hz. Why didn't REW attempt to fix this? I have the filter settings at their defaults so its allowed to apply an individual max boost of 9 dB (the default for overall boost seems to be 0 dB, so how could default for individual be 9 dB?) but it didn't attempt to fix it.
Can't really make any sensible comment without having the response and the target and filter settings and seeing what filters are generated.

lovingdvd 06-02-15 01:22 PM

Re: Tweaking filters after an initial filter set
 

Quote:

JohnM wrote: (Post 1221034)
No. Perhaps the midi interface isn't working reliably? Could try just sending the filters again, and view the filter settings on the BFD to see what has been transferred.

I did try resending the filters a second time after this happened and it didn't make any difference. I had to remeasure and then send the filters. I've seen this happen several times before on the very first measure.

I don't think its a communication / MIDI issue because when I first start I see the LED filter lights are lit. Then after I reset the filters and send an empty set (to erase all filters at the current BFD channel) I then see all the filter LED lights go out on that channel as it should. When I send the initial set of the real EQ filters, I see the comm working (lights flashing on cable and BFD) and when its done I see the 12 filter LED lights show back up representing data in each filter.

BTW, what's the quickest/easiest way to reset a BFD filter black - like I am doing it (sending an empty set)? I'm not sure if this causes the issue so I wonder if there's an alternative way to reset a channel other than that or manually deleting each filter in the BFD with the job wheel.

Quote:

Can't really make any sensible comment without having the response and the target and filter settings and seeing what filters are generated.
Here's a screenshot of the filters: https://drive.google.com/open?id=0Bz...RW8&authuser=0

And here's the MDAT file: https://drive.google.com/open?id=0Bz...NjQ&authuser=0

You can see these same filters by clicking on the first measure and going to the EQ window. When looking at this you can see the dip between 20 and 25 Hz that it didn't try to correct. Note that the Manual filters that show up in that EQ window are a few things I added after the fact.

Please let me know if this is helpful and why you think REW didn't try to improve the dip around 21.5 Hz. Thank you.

JohnM 06-02-15 04:07 PM

Re: Tweaking filters after an initial filter set
 

1 Attachment(s)
Quickest way to reset is send an empty set of filters.

You have very wide SPL spans on those plots, about 150 dB for the EQ window - any reason for that? Generally better using about 60 dB or so.

Individual filter boost can be much higher than the overall boost since the overall includes the cuts of other overlapping filters.

Main reason REW didn't do anything about the dip at 21.3 Hz is that it is very small, not worth doing anything to it, but boosting dips is generally not a good thing to do as that can create peaks when measured at other locations.

This is what I got running match response to target, after removing the manual filters. Results can vary slightly run to run as a random perturbation optimiser is used with the BFD.

Attachment 94226

lovingdvd 06-02-15 05:55 PM

Re: Tweaking filters after an initial filter set
 

Quote:

JohnM wrote: (Post 1222130)
Quickest way to reset is send an empty set of filters.

OK thanks that is what I have been doing.

Quote:

You have very wide SPL spans on those plots, about 150 dB for the EQ window - any reason for that? Generally better using about 60 dB or so.
Sorry I do not understand what you mean by "very wide SPL spans". What span and SPL are you referring to?

Quote:

Individual filter boost can be much higher than the overall boost since the overall includes the cuts of other overlapping filters.

Main reason REW didn't do anything about the dip at 21.3 Hz is that it is very small, not worth doing anything to it, but boosting dips is generally not a good thing to do as that can create peaks when measured at other locations.
Right. I understand what generally its not a good idea to apply boost. However in my case I do not listen any where near reference level and figure that 2 dB would be ok at 21.7 Hz. Where I'm confused is that I have the setting set to try and get it as flat as it can to 1dB, and adding a couple dB boost there should fall within the parameters on the Filters screen (less than 9 dB overall). So I'm surprised it didn't try it. Is there an option or what I can tell REW that I want it to be more aggressive with filling in gaps (without adding too much gain, which is what I thought the point of the individual max boost is - in this case don't boost anything more than 9dB, which is a lot less than the 2dB needed to flatten out around 21-22Hz?


Quote:

This is what I got running match response to target, after removing the manual filters. Results can vary slightly run to run as a random perturbation optimiser is used with the BFD.

Attachment 94226
Thank you.

JohnM 06-04-15 04:07 PM

Re: Tweaking filters after an initial filter set
 

Quote:

lovingdvd wrote: (Post 1222226)
Sorry I do not understand what you mean by "very wide SPL spans". What span and SPL are you referring to?

The span of the SPL axis, i.e. the difference between the top and bottom of the graph. On your EQ graph the top was set to 150 dB and the bottom looked to be about 10 dB, giving a 140 dB span. That makes everything look quite squashed. The recommended 45 dB to 105 dB range would provide a better view.

Quote:

Right. I understand what generally its not a good idea to apply boost. However in my case I do not listen any where near reference level and figure that 2 dB would be ok at 21.7 Hz. Where I'm confused is that I have the setting set to try and get it as flat as it can to 1dB, and adding a couple dB boost there should fall within the parameters on the Filters screen (less than 9 dB overall). So I'm surprised it didn't try it. Is there an option or what I can tell REW that I want it to be more aggressive with filling in gaps (without adding too much gain, which is what I thought the point of the individual max boost is - in this case don't boost anything more than 9dB, which is a lot less than the 2dB needed to flatten out around 21-22Hz?
REW assigns filters according to the area (roughly speaking the height of the peak/dip times its width), it doesn't bother assigning filters to tiny wrinkles in the response because there really isn't any point. Don't obsess over small features, the change in response when your head moves a couple of inches will be much larger.


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