REW Issue #1: Calibrating SoundCard

[JCD]

First, my setup:
I'm using an M-Audio MobilePre external soundcard running on Windows XP laptop.
(see below for pic of front and back of soundcard)

Next, my problem:
I've been trying to get REW working so I can take some full frequency sweeps of my speaker system. I've been having issues. The first issue is just calibrating the sound card. I'd expect my soundcard to be pretty flat across the entire spectrum.. but I'm getting the following soundcard calibration file for it:


Finally, my question:
What the heck is happening in that 100-600hz range? Is my sound card damaged somehow?
BTW, the issue is repeatable. Everytime I try getting a new calibration file, I have the same graph.

Oh, the loop I'm using for the calibration is a connection from the 1/8 stereo line out to 1/8 stereo mic input connection with a 1/8 to 1/8 stereo patch cord.

JCD

[Otto]

Hi there, JCD,

I think you want to use the line-in rather than the mic in. I think you'll have to use the "1/4" balanced inst/line input" jack, and a 1/8" stereo to 1/4" mono adapter, available at RS. Or you can DIY a cable. I think you may also be able to use the other input called "1/4" instrument input". I'd make that change first.

[JCD]

I've made the trip down to Radio Shack and bought a 1/8" stereo go 1/4" mono converter plug (part #274-348). I also bought a 1/4" mono to 1/4" mono patch cable. I've retried to calibrate the sound card with the following combinations and the following results:

1/8" stereo (stereo line out) to 1/4" mono chan 2 in:


Here is the result for 1/4" channel 1 mono input (on the front) to 1/4" channel 1/L output (on the back):


Here is the result for 1/4" channel 2 mono input (on the back) to 1/4" channel 2/R output (on the back)

And just for fun, here is the mic in to headphone out for the internal soundcard:


I'm assuming that the calibration files I'm getting for the MobilePre are still not what I should be expecting. Am I missing something still?

Thanks.

JCD

[brucek]

1/8" stereo (stereo line out) to 1/4" mono chan 2 in:

You're likely using too high a level for the test and the card is oscillating. Turn it down a bit when doing the test.

brucek

[JohnM]

That problem is caused by the internal monitoring not being muted, locate the direct monitor signal in the mixer and mute it. You'll find some other info on the card if you search the forum for MobilePre.

[JCD]

After many failed attempts last night to get this thing to work right and a short search for other MobilePre users issues, I brought my laptop and MobilePre into the office today to try some troubleshooting. I went through the following steps.

1. Connected the 1/8' Stereo line output to the channel 2 line 1/4" input
2. Muted the Direct Monitor, CD Player and SW Synth selections (see first pic below)
3. Clicked the "Settings" button
4. On the soundcard tab I clicked the measure button
5. From there, I tried to adjust the Channel 2 knob on the front so the output and input were the same. This was ESPECIALLY problematic as the input line would move ALL over the place. I don't think I was ever able to get a steady number, so...
6. I tried connecting to the Channel 1 1/4" input on the front. Same problem.
7. I tried using the 1/4" mono to 1/4" mono cable connecting the Channel 1 1/4" output to the Channel 1 1/4" input. I must have got lucky, as the second time I went for a calibration file I was able to get the second picture. However, when I tried it again, NOT CHANGING ANYTHING, I go the third picture, which is similar to what I got on several other attempts (and on the first attempt).

So, any ideas as to what's happening? I'm assuming that using the one good calibration file I have won't give me good results when I actually do a sweep later unless I get lucky again.


JCD

Pic 1


Pic 2


Pic 3

[brucek]

I'm assuming that using the one good calibration file I have won't give me good results

The first plot looks good. Let's hope you saved it as the soundcard.cal file.

Use it and move on to the measuring...

brucek

[JCD]

brucek wrote:

The first plot looks good. Let's hope you saved it as the soundcard.cal file.

Use it and move on to the measuring...

brucek

I did.. and cool! I was obviously assuming that since I was getting inconsistent results, I couldn't rely on future measurements.

Thanks!

JCD