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Need help with ETF and feedback into system...


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#1 of 51 OFFLINE   Dave Dahl

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Posted September 18 2004 - 06:00 PM

Hi all,

Lately I've been experimenting with the ETF software with my Radio Shack level meter.

I keep running into the same problem; the radio shack meter and my speakers (ML Ascenti's) keep getting into some hidious feedback loop. Nothing I do in the computer's mixer seems to help.

Any ideas? Also should the meter be set on 'A' or 'C' weighting?

Thanks!

Dave Dahl

#2 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 01:34 AM

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#3 of 51 OFFLINE   Dave Dahl

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Posted September 19 2004 - 03:33 AM

I appreciate the reply. Money's pretty tight nowadays and getting a new microphone right now is not an option. Hopefully I will be able to swing one by January.

Any other ideas?

-Dave

#4 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 03:44 AM

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#5 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 06:31 AM

Quote:
Quoted bt Craig
Dave - The Rad Shack is not near accurate enough for the ETF software... nor is the internal soundcard in your computer likely to be.
That is simply not true.

Point 1:
The soundcard has little to do with the measurement sequence, because the ETF program adjust's itself to the audio card response curve (i.e. even cheap soundcards perform to high tolerance specs with ETF).

Craig, you should verify the facts before making such inaccurate statements.

Point 2:
Yes, the RS SPL meter is not the epitome of a calibrated mic, but then neither is Craig's recommendation (the Behringer). Both use generic mic calibration files within the ETF software.

Personally, I prefer a professionally calibrated mic (with it's own specific calibrated file) to either the RS or Behringer, but either one is still useful.

Now to your problem:

A number of items to check and verify:
1) Is your soundcard a full-duplex soundcard?

2) You are using the LINE-IN on the PC from the RS SPL meter's RCA output (and NOT the MIC-IN)?

3) Is your mixer set up correctly?
-- Mic input turned off (i.e. MUTE)

Set the meter to the "C" weighting scale.

#6 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 07:37 AM

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#7 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 08:00 AM

Craig,

I agree, manners are important, but so is accuracy regarding the use of high-end sound cards with ETF (the expensive sound cards simply aren't required to get accurate results).

Those sound cards may well give more pleasing rsults when playing music, but they have no effect on the MLS-based signal manipulation of the ETF program.

I don't make unsubstantiated claims.

I've been using ETF for more than 5 years, since version 4, and have a very good understanding of it's fundamental capabilites.

What you handed out as advice didn't address the issues Dave was having and simply isn't accurate, that's all I'm trying to say.

#8 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 08:06 AM

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#9 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 08:21 AM

I have a mic compensation file for my system that includes both SPL and phase adjustments that ETF adjusts for.

Both the Behringer and RS SPL meter have generic SPL compensation files that can be used with the ETF program to adjust for the mic/mic-preamp's SPL curve response.

i.e. it's no problem for ETF to compensate and allow for this 11.5dB compensation, just as your professional mic should also have a compensation file, correct?

I happen to have an individual and specific graphic printout and diskette of my mic's compensation file, how about you?

#10 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 08:38 AM

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#11 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 08:48 AM

Craig,

It's not about being nice, it's about understanding the technologies you're making recommendations on to other people.

I have no problems discussing how to use tools, I simply don't like to see people giving advice that is not based on facts. i.e. wrong advice!!!

It is critical to understand the MLS-based signal technology and how that is utilized with FFT (Fast Fourier Transforms) to produce the frequency response, impusle response, energy time curves and other information available in the ETF software compared to simplistic RTA analysis.

Sorry to let you know, but RTA analysis doesn't even deal with the time component of sound like ETF does, so it won't really give you an accurate picture of anything except SPL levels. For instance it can't tell you what part of your SPL level is from modal reflections produced by the room, and possibly out of phase.

So Craig, are you in the business of selling any kind of audio equipment or services?

Just to be clear, I'm not in any business connected to audio services.

#12 of 51 OFFLINE   Craig Chase

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Posted September 19 2004 - 09:09 AM

Noone is paying me any money for anything in this business, period. The day I DO start in the audio field in a for profit situation, I will make that known publically.

Bruce D., I will do us both a favor and ignore you from this point on.
Craig Chase

#13 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 01:38 PM

Chris,
Last time I checked this was a free country, with free speech, so I respect you right to do so.

Likewise, I will continue to correct false statements made with incomplete or incorrect information. I feel it is critical for the members of this forum to get truthful and accurate information.

As you can see I've been a member of this forum since 1999. You are free to do anything you want, I will still respond with the truth.

Your answer about business ties seems to indictate you may be doing audio consulting for no money, is that true?

I also see you deleted all your responses in your posts. What are you afraid of?

#14 of 51 OFFLINE   Dave Dahl

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Posted September 19 2004 - 02:37 PM

Hi everybody,

I just returned from work to find my thread has taken somewhat of a detour. I'm not really sure what's happened so I think that I'll just go back to the original point...

Thank you Bruce for your concrete suggestions. I do have a full duplex sound card and the microphone input is turned off.

I did not think that the line input could cause feedback into the system. As for the mixer the levels are set right in the center.

-Dave

#15 of 51 OFFLINE   MikeTz

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Posted September 19 2004 - 02:52 PM

Dave:

I just began experimenting with ETF and it is a good idea to go through the "Getting Started" section to characterize and verify your computer sound card and familiarize yourself with the program. Acoustisoft, the ETF, company states in their literature that even older "low tech" computer sound cards will work with ETF because the software compensates for the card's response. The Getting Started procedure will verify that your sound card is OK.

Although Acoustisoft says you can use the Radio Shack SPL meter (C weighting) with their compensation file (downloadable from their support page) they recommend a calibrated microphone and a mic preamp. This equipment will give more accurate results as Bruce mentioned but it costs ~$250 if you buy it from them.

Check that your connections are tight (those 1/8" jacks loosen easily) and check that your sound card's mixer is adjusted properly. This can be done in the Getting Started section. Make sure you are using the line in for recording and that the sound card controller is set properly for the line out jack. Some sound cards have configurable jacks and they must be set to analog line in/out not microphone.

As a last resort, the Help section is actually useful. If all else fails you can use a test CD versus driving the system with your computer sound card.

MT

#16 of 51 OFFLINE   BruceD

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Posted September 19 2004 - 06:15 PM

Dave,

How about some more info:

1) What PC are you using?

2) What PC soundcard/mixer are you using?

3) What type of cables or adapters are you using (1/8" stereo mini phone plug)?

Are your cables hooked up as the Help section indicated?

Were you able to use the ETF program's calibrate function to set the SPL level to 75dB, or did the feedback loop start here as well?

Could it be mic feedback? I think the help section says to be sure everything but LINE(out) and RECORD are muted in the mixer.

#17 of 51 OFFLINE   Edward J M

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Posted September 19 2004 - 11:44 PM

This is from the TrueRTA trouble shooting section regarding a question on feedback. While the software packages are different, the application at the Windows Playback mixer might be the same. Worth a try......

Quote:
You may have the Windows Playback mixer set wrong. Open the Windows Playback mixer and make sure that you DO NOT have Line-In selected and that the Line-In fader is at minimum. Only the WAVE signal should be selected at the Play mixer. (a hard wired feedback loop can be created if you are in loopback configuration with the Line-In signal is selected and fader raised...not good) This can cause a wide range of strange problems.

Ed Mullen
Director - Technology and Customer Relations

SVS

www.svsound.com

"What we do in life, echoes in eternity."


#18 of 51 OFFLINE   Craig Chase

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Posted September 20 2004 - 10:12 AM

Dave, I hope you get your ETF set up working properly. If you want to try the Behringer sometime, drop me a line... It is not being used, and with funds being tight for you, I would be happy to send it to you...
Craig Chase

#19 of 51 OFFLINE   Craig Chase

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Posted September 20 2004 - 12:42 PM

You know... I was going to let this all slide, but when a "man" like BruceD decides to go after my character with snide innuendo and questions like "What are you afraid of", It is just too much to let go...

When one reads the help file in the ETF software, and want to know about calibrating a microphone, the first thing one must have is a calibrated microphone which is accurate above 500 Hz.

As it was clear Mr. Dahl was NOT in possession of such a microphone, I am unclear as to how he could properly calibrate the Radio Shack.

So, assuming Mr. Dahl IS able to get past the feedback problem, How does he calibrate the microphone...? If I missed something in the help section on this, I apologize.

I based the idea on the Behringer because two people whose judgement I trust, a local speaker designer in PA., and Our own Edward J M, have both said the Behringer will come out of the box as a pretty accurate... within +/- 2 dB from 20 to 20k.... microphone

David Fabrikant (Owner of Ascend Acoustics, and a very talented engineer) would not even consider allowing me to use the Radio Shack as a microphone. He was also not too impressed with the Berhinger, as it was, though superior to the Radio Shack, still not up to the standards he looks for. He DID opine that the Behringer would be ok for someone looking for reasonable results.

My opinion on upgrading the soundcard DOES go against what ETF advertises is needed. Again, with Mr. F's assistance, it was determined the Sigma Tel Audio soundcard in my laptop was not quality enough for the task at hand. My opinion was HIS opinion. When a guy with his experience and $100,000 worth of test gear offers help, I take it. HE actually took the time to use an M-Audio in his own lab... and was happy with the results.

After three weeks of learning, running sweeps, and forwarding said sweeps, Mr. F was satisfied that the system was within 1 dB of his reference measuring system, and also was easily reproducable with ANY speaker.

Since then, I have run sweeps on my:

Klipsch Belles, Onix Ref 3's and Ref 2's, Both sets of Ascend speakers, Rocket 550.2's and several others.

After all the assistance from David F., I am quite confident the measurements are accurate.

The accusation was also made that I am a "fake expert" ... When it comes to computers, I will be the first to say there is a LOT I don't know.

As far as my credentials as a soon to be retired audio reviewer, all I have ever said is I THINK someone could risk the return shipping based on my reviews... or $20 to $100, depending on speaker...

According to BruceD, He has been innundated with Private Messages from those who hold me in disdain, as someone who hurts the forums.

I would appreciate it if the people who really think so would be man enough to confront me directly, as noone has said anything to me yet.... That is called being a MAN.
Craig Chase

#20 of 51 OFFLINE   BruceD

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Posted September 20 2004 - 01:41 PM

Quote:
According to BruceD, He has been innundated with Private Messages from those who hold me in disdain, as someone who hurts the forums.

I would appreciate it if the people who really think so would be man enough to confront me directly, as noone has said anything to me yet.... That is called being a MAN.
Wow, and you talk about forum manners.

It certainly seems you don't have any. Posted Image

Quote:
the Sigma Tel Audio soundcard in my laptop was not quality enough for the task at hand.
My guess is that it wasn't a full-duplex sound card (being a laptop), and therefore wouldn't work correctly, but I could be wrong.


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