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Contact Us
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Morset Sound Development
+47 73915000
Persauneveien 25
7045 Trondheim, Norway
contact@winmls.com
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WinMLS User Tips and Hints
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Post your helpful tips that users find to make the setup, operation, or diagnostics of using WinMLS easier.
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Subject USB Pre
Date
Thu Sep 5 2002 11:06
Author Lars Morset
(morset@winmls.com)
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Jeremy, thanks for asking this question. We have tested some USBPre devices on different operative systems using WinMLS and there are some things that should be noted before using the USB Pre.
First of all, you have to download the latest beta to be able to test the USB Pre for transfer function measurements, since Swept Sine is needed, and this method is not included in the release yet (this was written 5. September 2002).
The USBPre works with SMAART since it mainly uses a measurement method not capable of getting as high signal-to-noise ratio (dual-channel FFT).
The beta can be downloaded from the lower part this web page:
http://www.nvo.com/winmls/downloadinfo/
This is what we plan to add about the USBPre to the next version of the WinMLS documentation:
The USBPre is a USB device with built-in microphone preamplifier and phantom power (48 Volts). Very nice, but because of synchronization problems it can’t be used for MLS measurements. This is because the AD and DA do not use the same clock. If you use the device peforming MLS measurements, you will see that the high frequency will roll off, and the roll-off will increase as you increase the total length of the measurement (the small difference in sampling frequency becomes more important when the measurement length increases).
What you need to do is to use the Swept Sine method instead of MLS. This method will work fine and has many advantages compared to MLS.
In the Measurement Selection Toolbar (found on the view Menu), select Sine Sweep instead of MLS. Please note that the output level is higher for Sine Sweep than MLS (one of the advantages). The level can be reduced in Measurement->Swept Sine Settings....
If you have selected Sine Sweep, you are ready to measure. But if you would like to measure the time of flight (distance between loudspeaker and microphone), you need to go to Measurement->Sound card settings... and in “Include Initial Time Delay in Measurement”, select “Yes, with loop-back, no end-check”. See “The first measurements walk-through” in the help file for more information about this.
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I tried to use my USB Pre device, but when I connected it, I got overload on all inputs and was not able to perform a measurement. What can that be (it worked very well a year ago)?
Pat Brown made me aware of that if you use USB audio devices with Windows XP, gaps in the record/playback may occur, this will destroy the measurement. We clearly saw this on Chris Horns laptop during the WinMLS training in Louisville.
There is some priority settings that should avoid this problem in XP, but I do not know how to do this. Any ideas?
Best,
Lars
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