View Full Version : Generating what appears to be white noise
September 1st, 2010, 10:22 PM
I use an Edirol UA-25 and running either v6 or v7, when I run a simple loop from the output back to the ref input and generate pink noise, the RTA display shows a smooth upward slope from lower left to upper right (see thumbnail). What do I need to do to restore the normal (flat) display)?
September 2nd, 2010, 12:45 AM
silly question but are you using a balanced TRS output cable?
September 2nd, 2010, 06:30 AM
Yes, TRS out to XLR in. Tested and swapped cables, to no avail.
September 2nd, 2010, 10:03 AM
Few questions and comments. The image is a bit grainy but it looks like you have the signal generator set to 0dB. Can you confirm that please. Also the signal being plotted is the measurement signal (left). The reference signal (right) looks like it has no signal and is just reading the noise floor. So the obvious question is what is driving the inputs? Are you certain that everything is routed correctly? Also is the signal generator sending to both the left and right output? I'm guessing that it's only hitting the left channel.
September 2nd, 2010, 01:28 PM
Generator output was set to -6dB. Routing was from the UA-25's L out (TRS) to the UA-25's in (XLR), no signal from the R out and nothing routed to the R in. I was originally going to check a PEQ via the magnitude display (splitting the UA-25 L out and routing one side back to the L in, and the other side through the PEQ), but with the PEQ flat the "white noise" response was the same on both measurement and reference sides. So after I tested all cables, reinstalled the UA-25's driver, I just repatched one side to get an image to post here.
September 2nd, 2010, 04:56 PM
Does the signal level go up and down and when you turn the generator on and off?
September 2nd, 2010, 07:31 PM
The signal follows the generator on and off, or varying the UA-25 output level.
Everything is now working correctly in v6, RTA display has a diminished but still notable upward slope (both measurement and reference), running ASIO in the UA-25, tested the PEQ in the magnitude display, all is good.
In v7, I deleted the default.xml and started over, now everything seems to be working, but running WAVE in the UA-25 (ASIO disappeared). However, the RTA display still has the same marked upward slope (both measure and reference) as in v6 as shown in the attachment.
September 3rd, 2010, 09:29 AM
When using a two channel device it's usually best to use the WAV drivers. They are generally more stable than ASIO drivers. The only time you really need to use ASIO is when using a device with more than two channels.
September 3rd, 2010, 09:51 AM
September 8th, 2010, 07:19 PM
Well that's obviously not right.
My guess regarding the disappearing ASIO option is that you have some issue with your ASIO driver that made it disappear. Unfortunately there's a bug (design flaw, perhaps) in Smaart 7 that causes it to remember every audio device it's ever been connected to, so if the driver went south at some point, you might still see it in Smaart until you deleted your config (default.xml) file.
That leaves the audio issue. I think the next thing I'd try would be to test the input and output stages of the device separately. If you have another known-good I/O device that's fairly easy, if not you could use an external signal generator to test the input section at least.
September 15th, 2010, 05:05 PM
I changed over to the WAV drivers for the UA-25 in v7, the problem is still there. Further investigation (testing some DIs) revealed what appears to be substantial harmonic distortion from the UA-25 device. I don't know if that would contribute to the "white noise" problem, but I will see if I can borrow another USB audio I/O device and determine if the problem persists.
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