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How to measure LFE out directly from AVR.

post #1 of 17
Thread Starter 
How do you measure the signal directly out of the LFE channel RCA on the back of the AVR and then plot it in REW?

I wish to compare Audyssey on with Audyssey off to see exactly what EQ it is applying.

I am assuming a RCA to 3.5mm adapter but don't know where to go from there.
Edited by Shinyav - 9/25/12 at 11:12am
post #2 of 17
Just get the signal into your soundcard using a line in or even in place of the microphone. Use whatever adapter is needed to make this happen. In my case this is either an XLR cable or an RCA to 1/4" TRS. Yours may be different. That is it really.
post #3 of 17
You simply use it like regular REW, with instead of the output of the mic to the input on the soundcard, its' the SW out to the soundcard. It's interesting to see what Audyssey really does, and it really depends on the amount of and difference between spots you measure at.

JSS
post #4 of 17
It is interesting to say the least. Expect big boost below 20Hz. I finally gave up on it altogether because I always felt I could do better manually and wasn't happy enough with some of the things Audyssey did to run it alone and call it good. I tried double dipping for awhile and coming in to further clean-up on top of Audyssey but I realized that was dumb and just clouds the water even more with unnecessary filters. YMMV. I would say if you plan to just run Audyssey alone and let it do its business it can make an improvement, but if you are going to manually start EQ at all just tackle it on your own and leave Audyssey off.
post #5 of 17
How do you guys EQ your surround speakers with REW? I can't seem to find the right mode to get my surround channels to work and the only solution is to connect my surrounds to the front outs and measure it that way.

I have a mode called quad bypass and sends the signal to all channels and will check if the sweep comes out thru the surrounds. If it does then all I need to do is mute every other channel. This would be very simple if it works. I doubt it though.
post #6 of 17
multi-channel stereo, and then just unplug the other speakers would be my suggestion.
post #7 of 17
Quote:
Originally Posted by beastaudio View Post

multi-channel stereo, and then just unplug the other speakers would be my suggestion.

I think I tried that but I will go thru all the multichannel modes again.
post #8 of 17
Can REW use two different sound cards? (one for playback and one for recording)

If so you could potentially use a HDMI audio device (like a new'ish Nvidia or AMD graphics card) to play the test tone to whatever of 7.1 channels you want (via 7.1 LPCM audio) and measure the output of the receiver into the 2nd sound card.
post #9 of 17
Quote:
Originally Posted by Stereodude View Post

Can REW use two different sound cards? (one for playback and one for recording)
If so you could potentially use a HDMI audio device (like a new'ish Nvidia or AMD graphics card) to play the test tone to whatever of 7.1 channels you want (via 7.1 LPCM audio) and measure the output of the receiver into the 2nd sound card.
yes. i did that to measure the response of the avr. set the output device in rew to the avr connected to the pc through hdmi and the input device in rew to the pc line in. loop the avr preout to the pc line in.

easy thing to configure if you happen to be running a htpc as your source.
post #10 of 17
here's my previous loopback measurement from the anthem mrx300 sub channel without ARC through the htpc linein.
sub_ch10.jpg
maximum crossover available for sub channel is at 150hz.
post #11 of 17
Thread Starter 
Alright got it working.



Pretty interesting. Not exactly what I expected.
My low end seems ok actually. Worst is a 1.5DB boost at ~9-15hz.
these were ran at -10DBMV I forgot and left my 80hz XO in place. So the boost at 90 is only a couple DB.

My goal/plan is to be safe at reference across what my sub can produce so ideally dynEQ wont be a problem.

As much as I want to do more and more of this on my own. I really like what Audyssey does to my mains. And EQing my mains on my own is way beyond my current knowledge.
Edited by Shinyav - 9/25/12 at 9:28pm
post #12 of 17
Thread Starter 
Is there any way to measure what audyssey does to the main speakers? I know it's not to wire them to my sound card somehow. biggrin.gif
post #13 of 17
Quote:
Originally Posted by Shinyav View Post

Is there any way to measure what audyssey does to the main speakers? I know it's not to wire them to my sound card somehow. biggrin.gif

You can put a voltage divider across the speaker wires.

If you're not comfortable with that as a < $1 DIY project you can buy a speaker to line level converter built for the car audio market.
post #14 of 17
Thread Starter 
Cool, definitely comfortable with it. If you have any specifics I would be interested. However, I will begin googling.
post #15 of 17
Quote:
Originally Posted by Shinyav View Post

Cool, definitely comfortable with it. If you have any specifics I would be interested. However, I will begin googling.

you only need 2 resistors. you can use other value according to your requirement of course.
head on over to epanorama for further reading.
post #16 of 17
Thread Starter 
Thanks will do.

Edit: link it perfect, thank you.
Edited by Shinyav - 9/29/12 at 9:15pm
post #17 of 17
Quote:
Originally Posted by Shinyav View Post

Thanks will do.
Edit: link it perfect, thank you.
don't forget to share your finding. however it might turn out. i've never came across anyone that does loopback measurement from their power amps back into rew before.

i would've done that but my speakers are running in full bridged. a hassle to take out the amp to get a ground reference.
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