Bad clipping problem

[Sniderhouse]

No matter how much I tweak the sweep, input and output settings, I cannot prevent clipping. At the point where I get the input VU to register something, the number at the top is always "-0.0". Even with the settings you see in the attachment, my measurement level is low, headroom goes to 0.0 and I get clipping and the "Impulse peak is not where it should be" message.

I have the volumes set so that my Galaxy CM-140 is registering ~75db, but when I do a Set Target Level, it comes back saying I'm at 90db. I'm not sure why the disparity from the Set Target Level and what the SPL meter is saying. I have the calibration file for the Galaxy loaded and the meter is set to slow and C weighting. I can only get input to register when the level on the SPL is on the lowest setting. I would expect that, if the SPL is reading ~75db and I set the level to medium, I would still get input signal, but I don't.

Since I always get clipping and 0.0db headroom on measurements, I don't give the resulting graphs much value, so I'm not posting them at this time.

Setup:

Galaxy CM-140 connected to line in of PC. Line out of PC connected to DSP1124 with Operating Level switch depressed (-10db). Output of DSP1124 to M&K MX-150THX subwoofer with low pass filter bypassed, phase + (tried - too) and variable input set to "reference" (12 o'clock).

Any help is appreciated.

Thank you,

Michael

[brucek]

It's as if you have a lot of noise at the input.

The red line and value at the top of the VU's show peak level. Yours is very high in relation to the RMS value.

Normally you would use a sweep level of -12dB (not -28db).

How were the levels when you ran the soundcard calibration routine? Did that all go fine?

brucek

[JohnM]

Also worth posting your Windows record mixer settings, and the Soundmax settings if it has its own mixer.

[Sniderhouse]

When I calibrated the soundcard with the loopback, the levels were all fine and I did not see the same peaking on the input that I'm seeing now. So I think I can safely rule out the soundcard. That leaves the Galaxy and the cable. The Galaxy is brand new but the cable is, well, crappy. Signal fidelity and integrity, be it of a musical or instrumental nature, needs to be maintained, eh? I'll swapt that out with one of my "good" cables and see if that cleans things up. If that isn't it, then it must be the Galaxy. I have a RS SPL meter I can fall back on to determine the failing part in this chain.

The sweep level you see was the end result of my continuous efforts to reduce clipping (as suggested by the clipping dialog box). When I replace the input cable tonight, I'll be sure to set everything back to "normal" before I run a Check Level and any measurements.

As for the Windows and SoundMax mixer settings, I muted all of the inputs save for "Line In" and muted all of the outputs save for "Wave". Though this on-board solution doesn't have much in the way of effects, it does have some sort of DTS processing, which I made sure was turned off.

Thank you for your suggestions, I hope to have better news to report tomorrow.

Michael

[brucek]

I'll swapt that out with one of my "good" cables and see if that cleans things up

Hopefully you have an adapter at the soundcard that has a stereo plug on it and then splits out the left and right channel, so that the mono cable from the Galaxy can plug into a left or right channel?

brucek

[Sniderhouse]

brucek wrote:

Hopefully you have an adapter at the soundcard that has a stereo plug on it and then splits out the left and right channel, so that the mono cable from the Galaxy can plug into a left or right channel?

Yes I do. The questionable cable is actually a stereo mini to stereo RCA, which I converted the right RCA to mono mini to plug into the Galaxy. I'll replace that cable with just a single RCA and use a stereo RCA to stereo mini adapter for the soundcard and an mono RCA to mono mini adapter for the Galaxy.

It's rather embarassing. I have probably paid way too much for high-end cables for my audio and video components but then use this cable of dubious provenance for the SPL meter and wind up getting burned.

[brucek]

The questionable cable is actually a stereo mini to stereo RCA

Which is easily checked by plugging the Galaxy into the Right AUX input of your receiver using the cable in question. The galaxy is a microphone, so dial the normal range and sing dixie into it and see how well it works.....

brucek

[Sniderhouse]

The cable was it! I got nice clean levels and a measurement that I can work with. The response isn't as bad as I thought it might be and should be easily remedied by some equalization. Now to try some filters and do some listening.

I do have some questions about re-doing my Audyssey and applying a house curve (like, when?), but that's a topic for another thread.

Thanks for getting me past this hump.

[brucek]

Great.

Remember when you equalize the sub, you start with the sub only (by disconnecting the mains). You connect the soundcard to the AUX or CD input of the receiver (in stereo mode only) and use your normal crossover so you can see how it tracks with the REW target set the same....

Then when the sub is equalized, you add the mains to check the integration and level at the crossover.

brucek

[Sniderhouse]

Right. That first graph was the soundcard direct into the DSP1124 in bypass. I then connected to the receiver to use it's crossover and before I disconnected the mains, I noticed a ground hum. I had already lifted the ground on the DSP1124 so I thought it must be the computer. Yep, when I disconnected the soundcard output, the hum went away. So I lifted the ground on the PC and I still had the hum! What I noticed was, even when the PC was off and the cable plugged in, I still got the hum. So I unplugged the monitor and voila!, hum was gone. So I wound up lifting the ground on the PC and the monitor (I'm running out of cheater plugs).

I have uploaded the initial filter, connected the mains and took some more measurements. Since my clipping problem is gone and I can now take reliable measurements, I'll start a new thread with my measurements and (inevitable) questions.

Thank you,

Michael

[brucek]

I thought it must be the computer. Yep, when I disconnected the soundcard output, the hum went away.

Yeah, I always discourage cheaters, but I admit that when I use my PC through my system for REW, I use one. PC's are the worst hum producers.....

brucek