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Signal Chain Loopback Measurements


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#1 3ll3d00d

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Posted 19 November 2014 - 08:20 PM

I thought I'd get the ball rolling from

 

It would be great if those with REW would do a simple loopback of their AVR, PEQ, Pre/Pro, amplifiers, etc. and post them is a thread dedicated to signal chain loopback measurements. It's so easy to do, I wonder why everyone doesn't do it. REW is free and you don't need a mic or anything else to do the loopback.

 

basic process is just to take an output from whichever device you're measuring and then feed that back to your soundcard (taking due care with levels if measuring an amp) then take a measurement in REW. A few things to bear in mind;

 

* make sure you have an appropriate (soundcard) cal file loaded to counter any purely measurement artefacts (e.g. a hpf on a line in is not that uncommon)

If your measurement covers multiple devices (e.g. perhaps you first loopback over your bd player and then you loopback over your bd player + processor) & you have a measurement for each stage then you can use the "A / B" trace arithmetic function to see the contribution of each individual stage 

 

 


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#2 3ll3d00d

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Posted 19 November 2014 - 08:22 PM

Marantz AV7005 7.1 Analogue Input in Pure Direct 

 

av7005.jpg

 

-1dB at 5Hz
-2.75dB at 3Hz
-5.75dB at 2Hz


#3 lukeamdman

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Posted 19 November 2014 - 08:33 PM

MiniDSP balanced 2x4

 

Balanced%202x4%20MiniDSP_zpsxfxczmik.jpg

 

 

Marantz AV7005 (Red line is XLR, green in RCA)

 

AV7005%20Response%20-%20XLRvsRCA_zpsnqdx


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#4 MKtheater

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Posted 19 November 2014 - 08:39 PM

Can we run a loopback with an HDMI computer?  I have everything using HDMI now so how do I do each component?  Basically I want to know my AVR LFE out, Sanway amp, etc..



#5 3ll3d00d

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Posted 19 November 2014 - 09:14 PM

Can we run a loopback with an HDMI computer?  I have everything using HDMI now so how do I do each component?  Basically I want to know my AVR LFE out, Sanway amp, etc..

what do you have for the input side?

 

you can use trace arithmetic here though. Take measurements adding one component at a time (over which you are taking the loopback measurement) then use A / B to see the diff between each measurement, this gives you the contribution of that component to the total rolloff.



#6 3ll3d00d

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Posted 19 November 2014 - 09:41 PM

Marantz AV7005 (Red line is XLR, green in RCA)

 

AV7005%20Response%20-%20XLRvsRCA_zpsnqdx

I wonder what the difference between your AV7005 and mine is. Is it just a measurement artefact or some difference in how we have it connected? Also, why would XLR have a different rolloff to RCA? 

 

do we need to post some details about the measurement setup to rule out any such variance perhaps?



#7 lukeamdman

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Posted 19 November 2014 - 09:45 PM

I wonder what the difference between your AV7005 and mine is. Is it just a measurement artefact or some difference in how we have it connected? Also, why would XLR have a different rolloff to RCA? 

 

do we need to post some details about the measurement setup to rule out any such variance perhaps?

 

I wasn't in pure direct mode, and I was measuring from the subwoofer outputs.  

 

My soundcard is a Behringer UCA-202, and I created calibration files for it so the response was perfectly flat before adding the AV7005 or the MiniDSP into the signal chain.  

 

Do ours really measure that differently?



#8 3ll3d00d

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Posted 19 November 2014 - 09:50 PM

I wasn't in pure direct mode, and I was measuring from the subwoofer outputs.  

 

My soundcard is a Behringer UCA-202, and I created calibration files for it so the response was perfectly flat before adding the AV7005 or the MiniDSP into the signal chain.  

 

Do ours really measure that differently?

possibly not actually (I'm on a slightly small screen atm), can you zoom in a bit? I used a 20dB wide y axis and 2-40Hz



#9 lukeamdman

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Posted 19 November 2014 - 10:07 PM

possibly not actually (I'm on a slightly small screen atm), can you zoom in a bit? I used a 20dB wide y axis and 2-40Hz

 

Unfortunately, all I saved was the pictures.  I don't have the files I could load into REW anymore,  



#10 Bossobass Dave

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Posted 19 November 2014 - 11:30 PM

OPPO BDP-105 & Bossobass SEQSS, both with 100 Hz low pass filter in line:

 

95797cb26d0f30aedf42d36a48887677.png



#11 Bossobass Dave

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Posted 19 November 2014 - 11:49 PM

Marchand BASSIS and Bossobass SEQSS MKII:

 

01ff09c7faac51df597d0c0c09b38dba.png



#12 MKtheater

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Posted 20 November 2014 - 09:57 PM

I am using a windows 8 computer with hdmi. I have my yamaha AVR hooked up to my Sanway via sub outs. I usually plug the computer HDMI into the AVR HDMI input 4.

#13 3ll3d00d

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Posted 20 November 2014 - 11:39 PM

I am using a windows 8 computer with hdmi. I have my yamaha AVR hooked up to my Sanway via sub outs. I usually plug the computer HDMI into the AVR HDMI input 4.

so you have a line in on a soundcard on the computer? if so, you just need to take the output from each device back into the soundcard and measure. You probably want to use a multimeter to check the output from the amp before you do so to keep it to normal line level voltages (or use something like http://www.avsforum....tructuring.html perhaps?)



#14 MKtheater

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Posted 21 November 2014 - 04:45 AM

How do I run the output of the amp to the line in?

#15 MKtheater

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Posted 21 November 2014 - 04:51 AM

I guess I could run the sub out and then compare it to AVR, drivers nearfield, and all together to figure out just amp.

#16 3ll3d00d

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Posted 21 November 2014 - 08:34 AM

How do I run the output of the amp to the line in?

I don't know exactly. I googled a bit more on this subject and it seems like it is more involved than I thought, for example http://www.diyaudio....asurements.html, so basically some sort of resistor network to provide a load to the amp and divide the voltage down to a reasonably level & then possible ground issues to deal with.



#17 BeastAudio

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Posted 21 November 2014 - 03:22 PM

Marchand BASSIS and Bossobass SEQSS MKII:

 

01ff09c7faac51df597d0c0c09b38dba.png

You can stop flexing your mettle now Dave :) Haha. So between the marantz, Mini, and Oppo (which I need to buy), I guess I would be looking at a pretty solid signal chain. The only other variable is the crest 7.5 but I know that has been tested as pretty flat to 2-3hz. Guess that shows pretty well in the speclab measurements we did that day :)



#18 MKtheater

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Posted 19 March 2015 - 03:05 AM

Here are sweeps of my subs front wall and rear subs. I connected the adcom to the rear subs as well to compare.


Green: Adcom rear
lower dark purple: clone rear
Maroon: front w/clone
top light purple: clone all subs

My UMIK does not have cal files below 10hz. This was at the MLP without touching gain, mic or anything. I tried matching the Adcom upper bass to the clone with the clones gains. The Adcom does not have gain controls. I should run a louder sweep with it maybe?



subs_zpsblfevqpj.jpg

#19 Madaeel

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Posted 19 March 2015 - 03:50 AM

Hey James isn't that odd how the rear FR matches the front?? Those responses are eerily similar like it was the same subs just another sweep. That green one looks more like a near field response than the dark purple.



#20 MKtheater

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Posted 19 March 2015 - 12:11 PM

My rear subs are about 6 feet away from the mic. The fronts are 14 feet away. The mic rolls off below 10hz without correction files. It is a UMIK from minidsp. I think I need to turn up the Adcom to get a better representation. My nearfield subs are not within 1 meter so room gain is kicking in but not quite as much as the front. All I did was turn the gain all the way down on each channel. Channel one runs the front array and channel 2 runs the back. The front array is 2 ohms and 8 drivers and the back is 4 ohms with 4 drivers.




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