# REW and TB Audio Advantage SRM question



## JonP (May 8, 2008)

I've been trying out various USB cards, looking to find a worthy replacement for the SB 24 ext that I've been borrowing from a friend for an embarrassingly long time... need to get it back to him!

Anyway, I got the above mentioned TB USB card... which basically looks to work OK with REW. For MLS impulse based measuring though, it seems to be a little "funny". I'm also a SoundEasy user, and am also looking for cards that will satisfy that more challenging program..

What I noticed with the TB SRM in REW, was that I'd get good FR graphs in loopback or measurment, but if instead of a single sweep, I used the multiple sweep feature (to average out noise) I would get a corrupted graph with terrible comb filtering... I also noticed that if I compare several individual single measurements, I see little variations between them at the high end rolloff.

Not sure what this is, small time/phase/? variations between sweeps making them not add up right? Something I'm not setting up right? I'm not moving the mic, really not moving stuff when I'm doing a cable loopback... And usually there's not much need to do the multi scan noise reduction... just want to know if there's something to fix this, or if anyone else knows something about it.


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## brucek (Apr 11, 2006)

> I'd get good FR graphs in loopback or measurment, but if instead of a single sweep, I used the multiple sweep feature (to average out noise) I would get a corrupted graph with terrible comb filtering


We've had this reported a few times, and each instance the result was a challenged computer. Sometimes it's a result of background tasks and the computer hitches a bit when running multiple or long sweep lengths.

Some people have some trouble with larger sweep lengths (128K, 256K, 512K, 1M). See this thread from this point.

brucek


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## JonP (May 8, 2008)

brucek said:


> We've had this reported a few times, and each instance the result was a challenged computer. Sometimes it's a result of background tasks and the computer hitches a bit when running multiple or long sweep lengths.
> 
> Some people have some trouble with larger sweep lengths (128K, 256K, 512K, 1M). See this thread from this point.
> 
> brucek


Hmmm... different looking problem than what I'm seeing, but I see the point that longer "sweep lengths" would be more difficult. What's the default, or suggested window length? I'm on 256k, forget if that's default or I set it there long ago...

I've returned the second TB AA SRM card, it had the same behavior including the "funny" impulse response. Took it back for a SB X-fi external, which won't even work... thing gives me nothing but the "USB device drawing too much current" error and the port shuts down... :hissyfit: I'll be taking that one back tonight... I have a few screenshots of the mentioned behavior and impulse response if anyone's interested.

Oh, I did check the laptop with the DPC Latency tester... found an oddity in that my internal Wi-Fi raised latency to 8000us, all the time... BUT, only when the radio was off, and the (Wi-Fi) network device was on. If I had the Wi-Fi radio enabled, latency was low, or if I had the network device disabled it was low. Weird... But either way, the TB card performed the same. The SB 24 ext worked fine...

I'll see if I can shrink down some screen captures tonight...


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## brucek (Apr 11, 2006)

> different looking problem than what I'm seeing


Yep, I was just making the point that a computer can make the difference...



> What's the default


128K - 1 sweep.



> I have a few screenshots of the mentioned behavior and impulse response if anyone's interested.


I'm interested.



> If I had the Wi-Fi radio enabled


Bluetooth, wireless, Wi-fi etc are all suppose to be off when using REW.

brucek


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