# Bad frequency responce with REW



## fwbutler (Sep 2, 2012)

Using REW I am getting a sharp drop-off below 100 Hz. This is direct wired to sound card, no equalizer in system. 
Other software shows a good response with same setup.
Does any one have any ideas?


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## fwbutler (Sep 2, 2012)

looks like the same problem as Re: Help with settings Thread. Was that resolved?


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## fusseli (May 1, 2007)

Do you have any soundcard or Windows sound device enhancements enabled? More importantly, did you create a soundcard calibration file for REW?


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## fwbutler (Sep 2, 2012)

No cal files of any type, no tone controls in circuit, set for mic or Z weight..., no house curve, LF cut off = 0, nor any filters, set for full range speaker.


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## JohnM (Apr 11, 2006)

Looks awfully like bass management in the soundcard, an 80Hz crossover filter with some glitches from mains hum pickup at 60, 180 and 300 Hz. If you attach the mdat file we can have a closer look.


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## fwbutler (Sep 2, 2012)

Thanks. a couple of files attached


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## EarlK (Jan 1, 2010)

If this ( above pic ) is still representative of the signal flow for your testing setup , then there are a few areas where things could go wrong .

- One, is engaging the high-pass filters of the 2 inputs ( on board #1 ) .

- As an aside, you appear to have setup a feedback loop ( by feeding signal from Mixer 1 to Mixer 2 ) . That's a no-no for any test setup ( feedback loops have the ability to contaminate the test results ) !

- You'd be far better off to follow this sites preferred wiring diagrams ( for use with an external pre-amp/mixer ) .










:sn:


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## JohnM (Apr 11, 2006)

In the first measurement the soundcard cal has been loaded as both soundcard and mic/meter cal, so it is being applied twice. The second has the soundcard cal loaded as mic/meter (which is OK, as long as it only appears once, but might get confusing if you later want to load a mic/meter cal file). 

The loopback measurement is unusually noisy (possibly some feedback) and suffers from mains hum pickup, producing spikes in the cal data. Better off not using that result.

The measurement that shows the low end roll-off is actually cleaner than the cal data, though it still shows signs of what looks like a small amount of feedback - the impulse response shows a secondary peak 20ms after the main peak and 33 dB down. The low end roll-off is so clean it is hard to imagine it being anything other than a filter being applied somewhere, pretty much bang on 18 dB/octave slope.


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## fwbutler (Sep 2, 2012)

Thanks for the help. good results!!
Tests with Sound card looped back
Gold cables
without mixers
without bass boost and 
sound card multi band equalizer at 0 ,
Dolby off,
as shown in diagram.
This gave good results so started to add items back in until problem re-appeared.
Found ATCF
All controls were not flat. Switches hidden be cabling on mixer 1 had been bumped. They were Low cut, 75 Hz, 16db / octave


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## fwbutler (Sep 2, 2012)

You guys are GOOD, I am impressed.
In case I forgot to say it *Thanks!*


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