My BFD - ETF5 experience (1 Viewer)

[brucek]

I think most participants here know what a BFD is, and if you don't, then you can read all about it on this web site first.
Link Removed edit new site URL
A low frequency response test for the purpose of monitoring the effect of entering equalization data into a parametric equalizer for a lot of us involves the so called "manual method".
This involves burning a CD with a sequential set of several second 1/6th octave tones, and then playing these tones through our sub(s), and measuring and recording the resultant SPL level at the listening position.
These readings are entered into an Excel chart that compensates for the deficiencies of the Radio Shack SPL meter, and then by observing the created frequency response graph we can determine what filter adjustments need to be made to make the graph behave the way we want.
This "manual method" generally works well, and no matter how easy and inexpensive it is, it has the disadvantage of taking an enormous amount of time.
Enter the ETF5 acoustic measurement software. This is a PC based software program that allows you to enjoy instantaneous readouts of your frequency response on your PC combined with a RS SPL meter. The company allows you to download a demo version that is surprisingly complete, but you can't save any of your files, although you can do a windows screen save to preserve your results. I thought it would be interesting to test this method, since there have been so many posts on this forum praising ETF5. Their web site, for further reading and understanding this software is at:
http://www.etfacoustic.com/
When I initially downloaded this software it would not work on my computer, but a subsequent reload of my soundcard drivers fixed that problem - duh. There is a nice web site from a member on this forum that is quite good regarding the hookup and use of this software at the site below, although it would be nice if there was a little more detail. I don't think he's finished...
http://www27.brinkster.com/jmag999/
Anyway, if you think the BFD has a large learning curve, well it's a walk in the park compared to this software and its full use. There is a lot to understand with this software and I decided to restrict my use to low frequency response tests to compare the resultant graphs to my "manual method" graphs. I was also interested in comparing a set of filters created using ETF5 with my set of filters created with the manual method.
Once you've mastered the hookup and use of this software, it's a joy to adjust a BFD filter and see the frequency response curve change accordingly in pseudo real time. The software has a sequential mode, where once its all set up and parameters and levels set, you can one-shot or take a reading automatically every 1.5 seconds while you watch your frequency response in essentially real time on the computer monitor while you adjust your filters. It also allows you to walk around your room with your SPL mic with its cable attached and see the effects on your response.
The ETF5 program corrects for soundcard deficiencies because one of the stereo channels of the sound card is shorted from input to output for correction. You can read about this on their web site.
One of the debatable points about the use of ETF5 is the use of a calibration file for the Radio Shack SPL meter. There is a calibration file on the ETF site, but it only calibrates above 500Hz. Not much use for what I want to do. I've read that ETF support has said, this is because the microphones they use (and sell) possess flat response down to 20Hz and that ETF won't work with values less than 500Hz. Well, this hasn't been my experience. It works just fine with all the low frequency values.
The "brinkster" ETF site mentioned above says to use the standard RS SPL correction values we normally use and even provides the file on the site for download. I feel the file on that site is actually backwards as far as its correction values are concerned. I'll explain....
I have reprinted the rs.cal correction file from the http://www27.brinkster.com/jmag999/ site. It is listed below for reference. This matches what I normally use for the "manual method" and is quite correct for that use. The rs.cal file is tabled in the order of frequency, then correction value, then phase. For example, when using the manual method, I take a reading at 20Hz, I add +7.5dBSPL to the reading because that's how much the RS SPL meter needs to be corrected at that frequency.
*****************************
10.000 20.000 0.000
12.500 16.500 0.000
16.000 11.500 0.000
20.000 7.500 0.000
25.000 5.000 0.000
31.500 3.000 0.000
40.000 2.500 0.000
50.000 1.500 0.000
63.000 1.500 0.000
80.000 1.500 0.000
100.000 2.000 0.000
125.000 0.500 0.000
160.000 -0.500 0.000
200.000 -0.500 0.000
250.000 0.500 0.000
315.000 -0.500 0.000
400.000 0.000 0.000
****************************
But, my observation is that this file above is completely backwards for ETF use and that the ETF program uses a negative logic on the compensation value numbers. And so if I have a compensation factor at 20Hz of +7.5, the entry in the rs.cal file should be 20.000 -7.500 0.000 and not 20.000 7.500 0.000
I come to this conclusion three ways. One is by observing the low frequency response graph, (while the rs.cal is loaded), during the initial setup level check of ETF5 to correct for your sound card deficiencies with the "both sound card channels shorted". The corrected sound card graph seemed exactly backwards if I entered the values as in the chart above. The corrected "perfect sound card" with rs.cal calibration should show 7.5dB high at 20Hz to correct for the SPL meter at that frequency. It showed exactly opposite this at -7.5dB low.
The second most telling indication is through experimentation with a single value to see what happens when I change it in the rs.cal file. For example, if I set the compensation value for 20Hz at 0.0000 and take a reading and observe the resultant value on the low frequency response graph, I could say, "the value on the low frequency response graph is too low because at 20Hz the RS meter is weak by a value of 7.5dBSPL". I want to compensate and "raise" the value on the low frequency response graph by 7.5dBSPL. If I enter the value in the rs.cal graph of 20.000 -7.500 000 it does indeed raise it correctly.
A third reason to verify that this is correct thinking is that if you look at the rs.cal file on the ETF web site that starts at 500Hz, I notice that as the frequency gets higher and higher, the chart values get progressively more and more negative. That would seem reasonable to compensate for the SPL meter since the higher the frequency, the worst the response.
Anyway, below are the values I used for my rs.cal file. Seemed to work pretty well. You could just use this file alone if you only care about low frequencies or simply preface the rs.cal from the ETF web site which starts at 500Hz. The ETF program evenly extrapolates the values missing between the entered values.
***************************
correct rs.cal file I use..
***************************
10.000 -20.000 0.000
12.500 -16.500 0.000
16.000 -11.500 0.000
20.000 -7.500 0.000
25.000 -5.000 0.000
31.500 -3.000 0.000
40.000 -2.500 0.000
50.000 -1.500 0.000
63.000 -1.500 0.000
80.000 -1.500 0.000
100.000 -2.000 0.000
125.000 -0.500 0.000
160.000 0.500 0.000
200.000 0.500 0.000
250.000 -0.500 0.000
315.000 0.500 0.000
400.000 0.000 0.000
****************************
One of the problems with using ETF5 of course, (besides the number of cables and special plugs required) is hauling your computer out to your HT area and setting it up. This could be enough to stop a lot of people from even considering using this method. I also ignored the fact that perhaps my room acoustics would be affected by my computer and monitor being in the middle of the room.
I fed the output of my computer soundcard into my processor using a "Y" cable and set the system to my usual crossover of 60Hz and shut my main power amp off. The managed sub signal then feeds my BFD and then my X-30 and Servo-15 sub.
Anyway, without any filters, the low frequency response graph produced by ETF5 was quite close to my manual method graph. This was encouraging. I paid special attention to my graph scaling of both methods so that I was comparing apples and apples. There was an anomaly in my ETF graph which was a very narrow negative spike up at 83Hz that I attribute to a small consistent tick sound in the ETF MLS signal that I attribute to my challenged sound card and computer. I ignored the small tick and resultant spike. You also have to be careful about the level setting of your record and volume control settings because you can get into a regenerative feedback situation and your system will break into oscillation. Careful setup of the record and playback levels is important.
I placed the ETF5 in automatic RTA Sequential Data Acquisition mode and entered a new set of filters to tame the peaks, just as I had done when using the manual method except now in about a tenth of the amount of time to do the job. This is where ETF5 shines. While you make the adjustment to any filter parameter, the response graph changes. The interesting thing here is that it gives you "eyes" to see how a filter at one frequency affects other frequencies around it, allowing you to "try" different filter parameters to get the smoothest response. I admit the manual method doesn't give you this insight or instant feedback control. It was interesting when I was using ETF5 and entering filters, particularly at one frequency, it wasn't the frequency at the top of the peak on the response graph that was the most effective center filter frequency to use. When using the manual method I always chose the frequency at the top of a peak.
Once I had completed my filters and the response was equalized to my satisfaction, I then changed the BFD program to the filters I had been using from the manual method to see what the response looked like using the ETF5 program. Well, the frequency response indicated by ETF5 while using my manual method filters wasn't quite as good as the set of filters I had just created using the ETF5 method. Both the ETF5 and the manual method ended up needing 4 filters to produce an equalized response. When I compare the 4 filters I created using the ETF5 against the 4 filters from the manual method they are fairly close, but different enough to make the ETF5 frequency response look much better using the filters I created with EFT5.
Now here's the interesting thing. If I then do a frequency response using the manual method and use the filters I created with ETF5, the resultant Excel graph looks poor, but looks great when I use my old filters I created earlier with the manual method.
So, I guess my question is, which method is correct and what set of filters do you use. ETF5 filters look great when I use ETF and the manual method filters look great when I use the manual method, but not vise-versa for each case. I'm not saying it's that far off, but different enough to make you wonder.
So for me, there's no clear winner. The problem with ETF5 is that it has a steep learning curve, and also requires a move of your computer system into your HT room. If you can overcome these two hurdles and can come up with the price of the full version and perhaps a better quality microphone, it would be a nice thing to own. I always advocate buying software rather than getting frustrated with partial functionality. It's nice of ETF to allow people to evaluate ETF5. Certainly the program is far more capable than just doing simple low frequency response tests.
For myself, I don't do this sort of measurement enough to justify the cost. I'm fairly quick with the manual method and it seems effective enough.
brucek

 

[Rick Radford]

Brucek,
>I've read that ETF support has said, this is because the microphones they use (and sell) possess flat response down to 20Hz and that ETF won't work with values less than 500Hz<
I'm guessing that probably came from me. I hope folks didn't misunderstand what I was trying to say.. which was (as I understand it) that the RS cal file and ETF do nothing for each other for LF response info. But ETF still works fine.. you just have uncalibrated LF response curves.
So it's not that ETF won't work below 500 Hz (or are you saying calibration values below 500 Hz?).. just that the program is not setup to utilize cal numbers below what is offered in the RS cal file on their site (I think the bottom number is around 315 Hz).
I ran a sample check both with and without the ETF RS cal file and couldn't differentiate the two graphs. ('course after I saw that and took a peek at the RS cal file correction numbers, I discovered the minimum value was 315Hz!) Thus, all my measurements come from uncalibrated RS mic input.
I figure that if I EQ the response curve flat with uncalibrated numbers, I end up with a nice house curve with about 6 dB gain as the freq drops.
Otherwise, if I want a truly flat curve, I need to manually plug in the RS correction values and plan from there. (BTW, do we know that the RS spl meters all operate reliably within some narrow dB range of each other for this correction file to be useful?) Does my logic sound reasonable?
Your manual vs ETF results are... interesting.

 

[brucek]

Rick,

You'll find if you enter the rs.cal file that I have labelled as "correct", that it does indeed properly compensate for the low frequency range.

brucek

 

[Sonnie Parker]

Great informational post brucek....as always.

I bet there a several ETF users out there that will find this helpful.

Rick, have you tried these values that brucek has posted to see how your response would look? I'd be interested in seeing the 2 compared.

 

[Rick Radford]

Interesting, Brucek. Then I am confused as to what the author of ETF was trying to tell me about ETF and LF corrections for the RS meter.
A while back I noted the same thing you did about the sign being inverted on those RS correction numbers... but didn't pursue it.
Let me do a little research and I'll be back.
BTW, you are right about the 500 Hz value.. I should have looked before I typed. 515 Hz, to be exact. Sorry!
Edit: Sonnie, you posted as I was typing. Glad to see you found this thread. No, I haven't had a chance to work with this new info yet.
I thought I'd get Doug Plumb's input on this to see if it's worthwhile breaking down the computer and lugging it into the HT room again.
Brucek, I really appreciate your indepth analysis as provided above. I'll be interested to see BruceD's comments should he decide to weigh in. He's been using ETF for about 2 years, iirc. And Guy Kuo has mentioned that he uses ETF as well. But I haven't seen him around here lately.
I haven't got past the LF response area yet. RE the ETF help file: as you can see, I still have much to learn about ETF. I don't know that I can add a whole lot more (at this point) to the existing site than Jon set up.
It appears the caveat I posted about the RS correction file may need to be amended.

 

[Steve Morgan]

Say, guys I don't know if you saw my post about getting hum from my sub with the BFD in the path but this is getting frustrating.I am using a cheater on the BFd and a cheater on the sub.What kind of innerconnects are you using from pre/pro to the BFD? BruceK when you connected the ETF5 software from you're soundcard to your pre/pro did you connect to the sub out or did you run to the line in on the sub? Thanks for the help,once I can play with the BFD I know this will get easier,but first I have to eliminate the loud hum.
Later,
Steve M.

 

[Rick Radford]

Steve, I saw your earlier post about the hum but didn't have any ideas for you. Sorry.
I use an AudioQuest Copperhead from the Onk989 to the BFD and a RS Gold A/V cable from the BFD to the Samson with 3 gold mono rca to 1/4 adapters.
I had a subwoofer hum but it was related to my cable TV input. I temporarily fixed it with a dual transformer setup from RS and replaced it with a Holland isolator that Ron Reda kindly sent me.
RS fix:
15-1253c 75 to 300 ohm transformer
15-1140b 75 to 300 ohm transformer
Holland isolator:
contacted Electrotex and ordered one of their Holland "Ground Loop Isolators"
See this thread.
However, I'm not sure that my solution will fix your problem.
>when you connected the ETF5 software from you're soundcard to your pre/pro did you connect to the sub out or did you run to the line in on the sub<
I know you didn't ask me, (I never let a little thing like that stop me!) but, fwiw, I ran my sound card line out to my CD input on my receiver and used stereo mode for testing. Since the left channels of the input and output on the soundcard were interconnected, I could only connect the right channel.

 

[Steve Morgan]

Rick,

Thanks for the help. I do not have cable just DSS and it is grounded.Funny, I have 2 large amps Parasound 2205a and a 2003a with no hum and the Paradigm Servo has never had a bit of hum.I am going to try different innerconnects from the Ref 30 to the BFd and see if that helps.If it does be ready for more questions about setting the BFd up and ETF 5.

Thanks,

Steve M.

 

[brucek]

Steve,

I connected the soundcard the same basic way that Rick did.

From the soundcard into an RCA "Y" splitter and into my CD input. This allowed me to check the sub with the mains at the crossover point for fun. Generally I was just testing my sub, so I had my mains amplifier turned off.

I use balanced cable input from my processor to my BFD, but RCA single ended works just as well..

Rick,

It's easy to see the effect of the rs.cal file without hauling your computer out of position. Just hook up the two channels of loopback on the soundcard that you would use in the initial testing. First do this with the low frequency signal without the rs.cal file and see the "perfect corrected response" flat line once you analyze the signal and display low frequency response.Then load the rs.cal file and observe the low frequency response and you'll see a perfect inverted RS SPL meters response curve instead of the flat line response. This shows the rs.cal file is applied. You can now adjust values in the file and retest and see the effect.

brucek

 

[Rick Radford]

Brucek,
For some strange reason, I woke up thinking about this thread today.
Those RS corrections you came up with.. reminded me that I had queried Doug Plumb about this when I first started working with ETF. That's when he told me:
"It probably looks like an easy task to add this calibration data - it isn't... The problem is that the internal processing works at only 500 Hz and above."
Now I have no clue as to how ETF is designed. But unless I misunderstood him or taken his reply out of context, you can't simply create the calibration file and make it work properly. I can't explain why; I can only take the author's word for it.
>ETF5 filters look great when I use ETF and the manual method filters look great when I use the manual method, but not vise-versa for each case.<
I wonder if the differences you see between the ETF and manual filters and lack of interchangeability has to do with your cal file you used.
You method of analysis to determine the cal file sure looks valid to me. I hope the ETF author will be able to provide some feedback.
It would be nice if this was a $50 program instead of $150. But as you said, the learning curve is steep.. and I doubt the support required could justify the lower price.
For anyone needing justification to buy a laptop, maybe this is a good reason! (get one with a full duplex soundcard) It would sure beat lugging that pc into the HT room.

 

[brucek]

Rick,

Now I have no clue as to how ETF is designed. But unless I misunderstood him or taken his reply out of context, you can't simply create the calibration file and make it work properly. I can't explain why; I can only take the author's word for it.

I guess what I'm saying is that if I remove all other variables except the rs.cal entries, then by changing the rs.cal file and seeing a resultant change in the low frequency response curve convinced me that the cause and effect is there and working.
Without any rs.cal file I get a perfect flat response when hooked up in the double loopback mode. If I load the rs.cal file and go to an extreme and for example change 50Hz to a compensation value of -25.000, then the effect is that the low frequency response changes by that much at 50Hz. This kinda proved to me that the rs.cal file I enter has the appropriate effect.
I could certainly be wrong about this. I just thought it would be easier to have the program adjust the weakness in the RS meter rather than me playing with the graph after the fact. This is why I thought you might play around with it a little bit. Maybe give it a try in the double cable loopback mode and see the effects of the rs.cal file in my original thread....
brucek

 

[Rick Radford]

>If I load the rs.cal file and go to an extreme and for example change 50Hz to a compensation value of -25.000, then the effect is that the low frequency response changes by that much at 50Hz. This kinda proved to me that the rs.cal file I enter has the appropriate effect. <
That sure is a convincing arguement to me!
I do not know how to reconcile your results with the info Doug gave me. I hope he'll jump in here and clarify the issue.
I'll try to play with it some next chance I have. (it'll give me another excuse to put off doing my taxes)
Edit:
>You also have to be careful about the level setting of your record and volume control settings because you can get into a regenerative feedback situation and your system will break into oscillation. Careful setup of the record and playback levels is important.<
Good point! Doug says he has re-written the mixer setup in the help file. He says:
>The mixer output needs to have all muted except the wave out. The mixer record input needs to have all muted except the line input. If this is done, it is not possible to have ETF give feedback.<
HTH.

 

[BruceD]

Some interesting points to consider:
The PC in the listening room is a problem, as ETF is sensitive to any background noise, especially that from the PC power supply fans, hard disk whine, CPU fan, etc. I think the program says it is sensitive to background noise as quiet as 50dB (a normal room during the day I think). I would recommend somehow keeping the PC in another room and using long cables or using a notebook PC on batteries (what I do).
The RS SPL meter when used in the "C" weighting mode is actually a custom response curve designed to respond to a frequency range that includes bass, but is weighted more toward the midrange. This means there is nothing wrong with the SPL meter's mic-response per se, just that the meter's needle is designed to respond to the "C" or "A" weighting scheme (both custom frequency response curves).
There is information somewhere here on the web that shows how to mod the SPL meter for flatter response (modify that "C" weighting curve).
Because of this I went to a calibrated mic-preamp instead. Actually I didn't buy the ETF setup, but instead bought a calibrated mic-wand and preamp kit. With the mic I got a printout of the calibration curve and a floppy diskette with the calibration table that I loaded into the ETF software. The mic and preamp I built Link Removed
That being the case, I never seriously used the RS meter for frequency plots, except originally to confirm that I could get the program working while I finished the preamp.
One of these days I will do a side by side comparison of my calibrated mic with the RS meter using the same SPL calibrated levels and compare the graphs. Now I'm still looking for a job.

 

[Sonnie Parker]

BruceD,

I've been told that you are da man with ETF. I was wondering if you might so kindly write up a detailed instruction guide for us. From setting up the various screens/options to using it.

It has been recommended by several that you are a good ole feller and probably wouldn't mind doing it for us.

If necessary I can input the info onto a page and upload it. I have plenty of webspace. I'd like to link to it from my BFD page.

Thanks is advance, if you don't have time, I respectfully understand.

 

[BruceD]

nt

 

[BruceD]

Sonnie,

If one takes the time to carefully read and understand the demo room files on the ETF site, it is a really great tutorial for the program.

Is there something missing from the ETF5 help, setup, and demo files that you think might be useful? Could you describe it?

I'd be happy to put some of my thoughts down.

Just be aware, I've been without a job for awhile and need to spend most of my effort on job searching.

By the way, great job on the BFD info.

 

[Sonnie Parker]

Thanks BruceD,
Let's see......if every member pitched in $1......lol...that still wouldn't get you where you need to be would it? heheh
What kind of work do you normally do? What field? Maybe I got some pull somewhere, yeah, right. I'm sure you believe this huh? On a serious note, I hope you do find a job soon. With your knowledge I wouldn't think it would take you long. Edit: VP Networking? No?
Actually I couldn't tell you if the ETF tutorial is missing anything or not, but I'd guess it is since there are several people asking questions about it and always needing help with it. (Not everyone, but I've seen several posts.) I suppose the ETF program can be used for several different things....similarly to Spectra Plus. I know there are several settings I had the dickens with on Spectra Plus. Finally someone spelled it out for me on what to input in the different setting screens and how to get my sound card setup properly. So, if we could get a step by step setup guide for beginners (for someone just learning about electronics and such) that would explain what you need to do to set it up just for measuring test tones or sweeps, I believe that would be nice. I really don't know squat about it so if I read the ETF info on their site, it wouldn't mean much to me. I struggled with the BFD forever before I figured it out, and I'm not sure I got it down yet. I'm really close though.

 

[Rick Radford]

Brucek,

I believe you are correct in your assessment of the ability of ETF to use the RS cal file you posted earlier.

I pointed out this thread to the author of ETF and requested that he join in if possible. I hope he will. I think ETF and Doug's input would be a valuable tool in the HT toolchest and feel that we'd all benefit from his presence.

IAC, Doug told me today that, "I was wrong, I think it will take data below the 500 Hz. It will not

calibrate a mic for you below about 500 Hz. My error."

I look forward to trying it out next chance I have to move the Pc into the HT room.

Thanks for your good work. For me, this issue would have remained a cloud over ETF had you not done the legwork to check it out.

But even so, I value the program enough that I'd still use it anyway. It's just much better now!

 

[Sonnie Parker]

Just in case I miss it Rick, I'd like to see your dual graph of before and after equalization (with the corrections). Please e-mail me when you post it, if you do or will that is. Or give me your raw readings and I'll stick them in my workbook and post a graph for ya. It's interesting to me to see others graphs.

Good investigating and clarifications from all you guys.

Thanks!

 

[Rick Radford]

Sonnie,
I've already done that. Here's a link to a jpg of the Excel graph. Compare the yellow and cyan (no RS correction) and the dark blue and magenta lines (with RS correction).
I'd post it here but have trouble with the GeoCities link.
In fact, you'll probably have to hit the "Go" button beside the address window after you click the above link to make it go there.
Here's the url for an ETF graph of the same thing. There is no RS correction applied here. Yet.