Subject Sound card types and settings Date Wed Sep 4 2002 08:35 Author Jeremy Johnston (jeremy_johnston@qscaudio.com)
I am using a USB Pre as a sound card for my laptop. The laptop does not have a line in so I cannot use the internal sound card. Likewise the USB Pre is a higher quality sound card and works well with SMAART and live recording applications so I would like to use it with WinMLS. Has anyone tried this? What should the settings be? Thanks

Subject USB Pre Date Thu Sep 5 2002 11:06 Author Lars Morset (morset@winmls.com)

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. ______________________________________________ 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

Subject USB Pre Date Thu Sep 5 2002 15:48 Author Chris Horn

. > 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. OK, I was able to solve this by D/Ling a WindowsXP update for the MS-Messenger (something like drop outs in conversations and echo canceling is described as error). It worked fine since (had Smaart run for a whole day w/o full scale clips - that's where it was seen easily). What you don't wanna do is update the USBpre software to v2.4.5. I am _not_ able to use the unit any more, neither with standard drivers, nor with ASIO drivers which were supposed to reduce latency a lot. I have to check with SoundDevices about this and will post the results here as soon as they reply. cheers Chris Chris Horn HORN Audio-Video-Systeme

Subject Driver Latency Date Fri Sep 6 2002 23:51 Author Lars Morset (morset@winmls.com)

Thanks Chris! Please note that latency (between start of play and record) should not be a problem with WinMLS. The latency must be known only in order to find the delay (or distance) from the loudspeaker to the microphone. If you are interested in finding this time of flight, it is easily done using the loop-back feature (see Measurement->Sound Card Settings...). Sound cards that has a sample-accurate constant latency do also exist. We recommend and sell the Digigram and Lynx sound cards. Please see the Sound Cards section in the WinMLS documentation (or help file) for more details. Best, Lars

	Subject Results from testing USB Pre Date Thu Oct 17 2002 13:18 Author Lars Morset (morset@winmls.com) File: USBPrewithWinMLSbeta.doc
You should be careful when using the USB Pre. Please see the attached document. Best, Lars

Subject Absolute Calibration (SPL) Date Wed Nov 20 2002 00:12 Author Lars Morset (morset@winmls.com) File: Why does my calibration not seem to be correct.doc

This is issues found by our new Swiss distributor which we really look forward to working together with: > (A) Inconsistency of calibration with measurement: > We calibrate the system (ch 1) using an external calibrator that generates > 93.8dB @ 1kHz. This seems to work fine. We then perform a measurement ("no > excitation (scope)") with the exact same calibrator in place and > we look at > the resulting measurement file (frequency response) which at 1kHz should > show the level of 93.8dB. The plot consistently shows a level that is a > couple of dBs lower than 93.8dB (around 88dB to 91dB). A workaround is to > shift the plot by a few dB in the F5 menue, but we don't like this very > much... :-) Any ideas why this could be the case? SOLUTION: SEE THE ATTACHED DOCUMENT (find the attachement as a link above). > eventually be nice to have some kind of dB SPL (A, C, fast, slow, even > better: Leq) implemented in the system, where the ultraprecise level cal > would be an absolute requirement. This can be done. Except fast and slow, which we plan to implement. Select the plot type Levels, click F5 to open the plot type settings and select dBA. You can check your calibration with this plot type as well.

Click here to return to discussion list