Using REW to test outboard gear

[drf]

Hi guy's, I have been looking with some interest as to whether REW can be used to test outbaord gear for more than just FR. Was hoping to use it to test S/N ratio. I am a bit slow when learning software (dyslexic ).

The first thing i have done is try to calibrate my soundcard, SBLIVE Value, using the line out and line in I managed to get a fullrange response like this:



couple of questions:

1. is this response standard of most soundcards? the +/-3dB after 200Hz seems wrong.
2. after i save this as a .cal file and it automatically loads when I run the measurement again shouldn't the graph then be flat?


sorry if this is simple but I just can't quite get my head around what is happening.

thanks
dr f

[brucek]

1. is this response standard of most soundcards? the +/-3dB after 200Hz seems wrong.

No, you have a problem. I would say your levels were incorrect for the test. Play around with the input output levels until the graph doesn't oscillate like that.

Here's my soundcard graph using the same scale axis as you used.

2. after i save this as a .cal file and it automatically loads when I run the measurement again shouldn't the graph then be flat?

What do you mean when you say run the measurement again. Running the soundcard measurement again will only produce another soundcard measurement file.

But, if you have a proper soundcard file it will make response measurements accurate because the results will remove the response anomolies caused by the soundcard. If you want to see that this system is working, you can take a normal sweep measurement of the piece of cable shorting line-in to line-out. It should be flat.

Was hoping to use it to test S/N ratio

Mmm, I don't really see how you could do this?

brucek

[JohnM]

That response is typical of what you would see if monitoring was turned on in the soundcard or there was some internal feedback, check the advanced controls in the SBLIVE mixer and make sure monitoring is turned off and that the line in is not being mixed into the output.

[drf]

Thanks, I meant to say that when i ran the measurement again it wasn't the soundacard measurement but the automatic measure like the help file says, however the result was exactely the same. I have tried adjusting the mixer controls for SBlive and now I have a dead flat line, no ripples no dips, nothing.
At the bottom on the right the in the details/results it says the flatness is +0dB,0dB and zero% harmonics.
Is it posible that my drivers/other windows applications are a bit iffy causing undesireble results?

cheers,

dr f

[brucek]

like the help file says, however the result was exactely the same

Did you switch to a TAB (i.e. left or right) other than the soundcard to do that automatic measurement? Lots of people forget to do that after the soundcard test when they want to test the measurement out.

brucek

[drf]

Thanks, I seem to have goten rid of that wave by muting the record channel (I assume this was acting like monitoring as the manual says you should hear what is being recorded).

I still get a perfect response when i do the initial soundcard test, Because it is perfect it won't allow me to save a cal file. I am sure the result should not be this good. Any other ideas would be appreciated.

[brucek]

Any other ideas would be appreciated.

You are using stereo 1/8" plugs on the shorting cable between line-in and line-out for the calibration test?

You have initially set up the Measurement level, Input volume and SPL Calibration prior to the test?

brucek

[drf]

yes and yes, I am just wondering if my card (being a cutdown value bundle) might not be suitable.
It appears record monitoring can only be trully turned off on the better cards.

cheers
dr f

[JohnM]

It should still work OK. If you post some screenshots of the soundcard mixer settings and the input and output settings you have set on REW we might spot what's wrongly set.

[drf]

What have I done wrong?






I have tried muting the line-in and adjusting the volume but it doesn't seem to effect the measurement.

thanks,
dr f

[brucek]

You have no output device in REW selected (i.e. SPEAKER).

See how both the WAVE and OUTPUT levels are grayed out......

brucek

edit:attached are my mixer and REW levels. See the WAVE and OUTPUT is not gray.

[drf]

Hmmm, I have set the levels exactely like yours only my wave level is still grey. With the levels set this way I get a measurement just like the one I first posted.

After alot adjusting then measuring I have managed to get this:



using these settings:



but the wave is still grey and it is so finicky that if one level changes even minutely the response is full scale noise or a big sine wave again.

thanks for all your help so guys.
dr f

[brucek]

Well, I didn't really mean for you to use the exact same values that I use. Yours will be different.

I just showed you the picture so you could see my mixer and the non-grey output and wave controls.

When you pull down the Soundcard and look for the Wave control name, does it look like this picture below?

Perhaps you'll have to force the selection instead of using the default. i.e. PC speaker select.



brucek

[drf]

brucek wrote:

Well, I didn't really mean for you to use the exact same values that I use. Yours will be different.

I just showed you the picture so you could see my mixer and the non-grey output and wave controls.

brucek

I figured that, but i also figured it was as good a place to start as any. Yes the soundcard control looks exactely like your picture. i can select other option like pc speaker, also my card has a line-out but it does not get a mention anywhere in REW, on the mixer or even in the Soundcards documentation.

cheers
dr f

[brucek]

I would reload my soundcard driver. There is something very strange here.

Can you also post a pic of your Windows Playback and Record mixer (not the SB mixer).

brucek

[JohnM]

The main problem looks to be that your record device is set to the midi input, click the arrow in the REC selector and choose Line In as the record source, it should then show the same image as appears above the Line In. If a red + is shown for advanced controls set it for record withot monitoring, also try with and without muting the line in control.

[drf]

the record device was set to line-in however there is no option to turn off record monitring (manual says its not an option on my card) I had it temporarely set to midi to see if record monitoring was only on the record channel or wether the monitoring was for every input regardless.

here are the windows control shots, they have no record level control. I simply split the image so it wasn't too wide for the forum.




Thankyou for your time and patience guy's.

dr f

[brucek]

Did you try and unload the driver and then reload it, because this makes no sense to me.

[drf]

yes, I have even tried third party drivers. My gut feeling is that this card (being the cheaper cut down) is just not suitable. maybe I have overlooked something simple, I will see if there are other drivers and such for this card.

[brucek]

Are there any errors being produced in the REW debug files?

Every time REW is started a debug file is created. A total of 9 are kept before deletion.

They're text files and easily read with notepad. If there are no errors, it just says REW started..

Their filenames are roomeq_wizard(1-9).log.txt and are located in c:\Documents and Settings\yourusername.

brucek

[drf]

they all say this:

Dec 4, 2006 9:37:08 PM roomeqwizard.RoomEQ_Wizard main
INFO: Room EQ Wizard started

except the first 2:

Dec 3, 2006 10:15:31 AM roomeqwizard.RoomEQ_Wizard D
INFO: win32com.dll copied to C:\Program Files\Java\jre1.5.0_05\bin\win32com.dll
Dec 3, 2006 10:15:32 AM roomeqwizard.RoomEQ_Wizard main
INFO: Room EQ Wizard started

[JohnM]

When you click on the drop-down arrow of the symbol in the right hand REC column of the Creative mixer what options does it show?

To see the Windows record mixer settings select Options -> Properties -> Adjust volume for Recording (it defaults to showing playback).

[JohnM]

You'll also need to use the Creative mixer REC slider to set the record level, rather than the REW control. It was set to 0 in your mixer screenshot.

[drf]

here are the settings i used to get the results in post 12:



If I vary these settings even minutely it goes from all noise to a perfectly flat response (and/or not enough signal).

[brucek]

Maybe we can break this down between input and output.

When you use the REW Signal Generator at a -12dB setting, are you able to output a 50Hz sine wave tone and adjust the mixers Volume and Wave level to produce a good output that you can control with the receivers volume control to obtain 75dBSPL on the RS meter?

With the mixer and REW running, does adjusting the mixer Volume control alter the REW Output level figure?
Does adjusting the mixers Wave control have any effect on the level figures of REW?
Does adjusting the mixers Line-In and REC level have an effect on the REW Input Volume level figure?

With that 50Hz signal playing at 75dB and your RS meter hooked up, click the RED button on the REW SPL meter. The SPL meter should show the SPL level and the input VU meter should also show the signal level. Does adjusting the Input Volume control on REW move the level smoothly up and down. If so, set the Input volume for a -12dB setting on the VU meter.

So while running this test, are you able then to have a -12db output and -12dB input on the VU meters with the RS meter reading 75dB? If so, then click Calibrate and set the REW meter to 75dB and REW is calibrated now manually (you could use sub pink noise for better cal).

brucek