ALL Digital processor

[Athomas]

Hi Guys,
Hope you can advise me here on this one.

I have a pre that has all DIGITAL inputs, no ANALOGUE, how can i connect my soundblaster 24 bit live card to this properly?

My soundcard has optical and coaxial outputs and I am wondering if I will be able to use these connections properly?

I HAVE had a bash at it, but i get some pretty strange things going on.

When i connect and run the pink noise to set the mic, I always end up with like 40db of noise registering in REW and its dead quiet in the room. And I get some feedback from the speakers?

I am using a ratshack digital meter if that helps.

thanks for the help,
Andrew

[brucek]

REW requires the soundcard to be calibrated using the analog line-out and analog line-in. If your preamp doesn't have analog inputs, it can't be used with REW. If you're attempting to test or equalize your subwoofer, you could connect directly up to the sub amplifer though.

brucek

[Athomas]

Hi Bruce,

O.K thanks for the reply. I will see what I can come up with.

I dont use a subwoofer at the moment.
I may change my processor then for an outlaw one which I have been fancying.
Now I have the required ammunition to convince the wife! haha

thank you very much,
Andrew

[brucek]

I have an all digital processor, no analogue inputs and as you explained this cannot be used with REW. You stated in your reply to my question that I can use REW directly conected in the path of my subwoofer. Could you explain how i would do that ? I am quite happy to move my computer upstairs for testing (no laptop) I have a soundblaster card and all cables i need plus the radio shack digital meter , Cal file etc.

Can you help??

Andrew, the only difference between using the receiver in the testing of your sub with REW and going directly to the sub amp is that the sub amps own volume control will control the volume when you're setting 75dBSPL at the listening position (rather than the receivers volume control being used).

But first, before you move your computer to hook it up to the sub amp, you need to do a soundcard calibration and create the cal file for it. This involves connecting a single RCA cable between the soundcards right channel line-out to the right channel line-in. If the soundcard has 3.5" stereo plugs for line-in and line-out you'll need the splitter adapters to break out the right channel.

Once the soundcard cal file is created, connect the right channel line-out of the soundcard to the sub amp, and connect the RS SPL meter to the right channel line-in of the soundcard and set up the levels using the Check Levels routine. Then run Calibrate SPL and then do a Measure from 0-200Hz.. You won't have the benefit of the receivers crossover in place, but you can certainly equalize your sub.

brucek

[Athomas]

Hi Bruce,

Excellent! Thanks very much for the reply. So effectively, If I am understanding this , I connect my soundblaster card to the computer FIRST, and create a .cal file that REW can use. Then after this is performed and stored, I can then move my computer to my HT room and connect it to my poweramp (pro-poweramp) and use its gain setting to achieve a 75db or whatever level tone.

Then after REW is done I Manually enter the filters it sugests? Do I have the grasp of things there?

Tremendous of you to respond today Bruce, really apreciate it!

[brucek]

If I am understanding this

Yep, you've got it.......

Just be sure you've gone through the soundcard cal and saved the file for REW to see, and then once that's done, it's a good idea to do a Measure of the loopback cable before you remove it. The result should be a perfect flat response (if your soundcard cal file is correct).

brucek

[DrWho]

brucek wrote:

REW requires the soundcard to be calibrated using the analog line-out and analog line-in. If your preamp doesn't have analog inputs, it can't be used with REW.

Not true.

It sounds to me like you don't have REW configured to send the test signal out the proper channel. And it also sounds like you've got monitoring turned on for your recording channel (which would be configured in the soundblaster software). You don't need to monitor the channels you're recording on...so just go ahead and mute your microphone in the creative software.

[brucek]

Not true.

How do you propose to calibrate the soundcard without using the analog I/O?

brucek

[Athomas]

Hi Guys,

Thanks for the replies. I have spent all last evening getting it up and running... I have a graph to post of my measurement, and would appreciate any insight.. I dont know if it looks good or not!

I will figure out how to post it and we shall see.

Thanks again

[Athomas]

I hope this works...
This is without any smoothing , do i need to add the smoothing???


graph below.

[Athomas]

WITH smoothing then, just for kicks!
What does this mean ?? is it any good??

Graph below

[brucek]

will figure out how to post it and we shall see.

To create a graph, simply click the little floppy icon button in the bottom left hand corner of the REW plot. It saves a jpg of 800 bits wide.

To post the jpg graph, read this

the problem is that the rew program doesnt come up with any filters, and its got me stumped to be honest

To create filters, REW must have peaks to work with that are above the target line.
Since you're not using a crossover in your measurement, you will restrict your Find Peaks range (in the Filter Tasks pull down) to 20Hz-80Hz.
Then be sure there are peaks above the target line (if not you may adjust it up or down using the Target Level thumbwheel.
Once peaks are found, select Assign Filters and then Optimize PK Gains & Q.

BTW, don't use smoothing for sub graphs. Use the scale of vertical = 45db-105dB

brucek

[Athomas]

Corrected graph, no smoothing,

[brucek]

Is this with no filtering also?

brucek

[Athomas]

No filtering as yet bruce, because i was unable to get it to tell me what filters to assign! hehe!, but I am working on that now.

[Athomas]

O.K.

I now have the 4 filters suggested by REW, as you know, I now have to dismantle my P.C and take it back upstairs to remeasure after I apply the filters to the BFD, I will probably have to post the results tomorrow as I may not have time today.

Thank you all for your help, and I hope it gives good results!!

All the best,
Andrew.

[DrWho]

brucek wrote:

How do you propose to calibrate the soundcard without using the analog I/O?

brucek

It's gotta end up analog somewhere along the chain.

Really all you'll be looking for is where the LF corner is. There is no reason not to trust line level components to be accurate within +-.1dB through the passband...with the cheap measurement mics being used, the measurement isn't going to be more accurate than that anyway.

[brucek]

There is no reason not to trust line level components to be accurate

So you support not creating a soundcard calibration file since the microphones used are already inaccurate?

brucek

[DrWho]

I'm only suggesting an engineering perspective, not a scientific one.