Setting Levels in SW

[Anthony]

Okay, this is more of an exercise for my own testing, but I figure I'd post a topic here and let other chime in. Perhaps some of the power users of SW will notice and migrate over here to help (their boards seem pretty dead, but the SW hasn't been updated since 2003).

that being said, it's still a fantastic tool (or so I've read).

Right now I'm in the process of calibrating my sound card for use in SW. This involves setting levels, channel difference, etc. Right now, I'm stuck on the levels and harmonic distortion measurements.

I have an M-Audio MobilePre USB sound card. It has XLR mic in (L/R), Bal/Unbal instrument jacks (L/R), Stereo line in, and unbalanced line out.

I have a ticket in with the M-Audio support to figure out voltage limits and input impedance on all these.

The first battery of test is to set levels and avoid clipping. On most soundcards, this is done by varying the line in, master volume, and wave levels in the mixer. For the MobilePre, I also have preamp gain knobs on the front of the unit. This is causing a bit of a headache.

The sine wave signal seems to clip at too high output levels independent of input levels. To top it all off, what looks good on the output signal (no clipping) can sometimes still flash a clip indicator light on the front of the unit. So I'm trying to stay under the units clipping threshold, get a clean waveform, and good output (higher the better for Signal to Noise measurements) -- all while fiddling with 4 differnet controls that are not intuitively connected.

Any help on this is appreciated.

Also, I'm trying to get SW to do a good plot of Harmonic Distortion of the soundcard, so I can use that to set levels. Sometimes a non-clipping amp can still have a lot more distortion, i.e. turn down the signal even further. I'll shoot an e-mail off to RBJ and Claudio Negro -- both major contributors to the online help of SW.

If any of you have any advice, specifically regarding balancing out all those inputs and output controls for a good signal, I'd appreciate it.

Thanks,
Anthony

[Otto]

Hi there Anthony,

First, the most basic and stupid question -- what's SW?

Second, can you do what you want with REW? I only skimmed your post, but it seems like REW could do this type of thing...

[Anthony]

Speaker Workshop.

REW can do the frequency response stuff, but SW can measure driver impedance, driver FR with established start/stop frequencies, and with a jig, you can use your soundcard to measure resistors, capacitors, and inductor values.

That, and it has a great crossover design tool and can measure driver distortion (both harmonic and intermodulation).

Basically, I got as far as I could with REW (from a speaker design perspective), so I decided to try SW. REW is still #1 for room measurement and subwoofer EQ, though.