# REW - Possible?? Measuring using Pink Noise from Source Player



## media2368 (Apr 19, 2006)

Hi All Gurus,

This is the FIRST Thread that i posted here.

I have 3 questions here to ask about REW:

1) I am using a External USB sound card with REW, SPL meter will connect to LINE-IN of the sound card. Can I not use the Sound care's LINE-OUT to AVR but just use my source (DVD Player) that has already connected to my AVR to play the Pink noise for Freq Resp measuring? Any trade-off or anything that I need to adjust in order to get REW to work properly? 

2) If I use the sound card's LINE-OUT (let said LEFT line-out) connect to AVR's Left input, will it the FR measure correctly? The reason I asked it because to my understanding low freq found in ALL CHANNELs (not only LEFT) so will the FR being measure correctly by using this connectiong method?

3) In REW Tips found in this forum, under View and select 2 Impulse Response Controls. I DOES NOT ALLOW me to Change the Pre-ref Window Width (ms) to 125. Is it because I didn't take any measurement so it doesn't allow me to change the PRe-ref Window Width?:dontknow: 

Hope you guys can assist me on the aboved questions.

Thank you in advance. 

Media2368


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## brucek (Apr 11, 2006)

I don't see the upside in this idea. Simply use the LINE-OUT provided by REW and you'll get the advantage of all the features provided with pink noise, log sweep, linear sweep, sine wave and square wave. The program is calibrated to be used with both input and output. The soundcard calibration is an amalgamate of the inadequacies of the input and output.

You can use any available line input on your receiver - AUX / CD / DVD / TAPE etc....

You can't change the pre-ref window until you take a measurement.

brucek


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## media2368 (Apr 19, 2006)

Hi Brucek,

Thanks for your reply. 

But is Single Line-Out (Sound Card) to Single Line-In (AVR) good enough for measuring?

Someone told me to us Y-Adapter from Single Line-Out (Sound Card) to L+R Line-IN (AVR)...which is correct? :yikes: 

And I have heard that measuring the signal from the Source (DVD Player or CD Player) will be much accurate...afterall the Source is THE ONE that play Movies/Music...:scratch: 

Sorry I am not trying to urgue....just too confuse:blink: ...hope you can help..Thank you so much.


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## brucek (Apr 11, 2006)

> But is Single Line-Out (Sound Card) to Single Line-In (AVR) good enough for measuring?
> 
> Someone told me to us Y-Adapter from Single Line-Out (Sound Card) to L+R Line-IN (AVR)...which is correct?


Both are correct in that the plugs on a soundcard are stereo, but we only want to use one channel for both input and output.

So you must plug in a stereo adapter that has an 1/8" stereo jack on one end and two RCA plugs on the other end. Now you only use one of the RCA plugs.

You'll need two of these adapters hanging out of the back of your soundcard.

brucek


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## media2368 (Apr 19, 2006)

I am using this external USB sound card.









So I can just use one RCA Plug (from sound card either L or R) to one RCA Plug (from AVR either L or R). 

But if I am going to measure the Main speakers, then I will have to connect BOTH L + R from Sound card and AVR.

...OH..I think of a question..but might sound stupid..if I connect BOTH L + R from Sound card and AVR to measure Subwoofer freq respond, will it play louder than using just L to L from sound card and AVR? (Or REW will automatically adjust the sound level on it software side to make sure that it measure correctly? Will it affect the SPL level calibration for the subwoofer?)..

Sorry..my understanding is really bad...hope you have patience to reply my doubt... I really appreciate..Thanks.


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## brucek (Apr 11, 2006)

> So I can just use one RCA Plug (from sound card either L or R) to one RCA Plug (from AVR either L or R).


Yeah, didn't know you had an external. Yep, if it has separate left and right RCA input/output, simple use one.



> But if I am going to measure the Main speakers, then I will have to connect BOTH L + R from Sound card and AVR.


No, still only use one, but when you plug this *one* into the receiver, use a Y-splitter to left and right in.

brucek


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## media2368 (Apr 19, 2006)

Hi Brucek,

Thank you so much for your time. And my doubt for all 3 questions have been clear.

Here I have another question for REW.

After measuring the Freq resp > Find Peak > Optimise PK Gain & Q, is there anyway to apply Filter on the Screen and do another step of Find Peak > Optimise PK Gain & Q > 'Apply Filter on Screen' until I am satisfy with curve before we apply the exact Filter data to the BFD?


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## brucek (Apr 11, 2006)

> until I am satisfy with curve before we apply the exact Filter data to the BFD?


Absolutely, except you don't do another FIND PEAKS, etc.

The FIND PEAKS routine is a great suggestion for filters. Once you've done this step though, now is when you start to add more filters manually using the dynamic representation on the REW screen as you adjust them to see the predicted results. 

You can also modify the suggested filters too if you like.

Usually, what you see in the end result on the REW screen after playing around with filters, will be the actual result after you enter the filters into the BFD and remeasure.

The only caveat there is that any filter with 'gain' may not result in exactly the predicted result. Sometimes its fine ane sometimes its not. If you throw gain at a dip and it responds - great. If not, remove the filter.

brucek


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## media2368 (Apr 19, 2006)

Thanks Brucek,

I will let you know if I have any further question. Cheers!


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