Mark Payne Posted December 7, 2006 Share Posted December 7, 2006 This may be a bit specialist so forgive me. I am trying to measure impulse response using Smaart Acoustic Tools, my lappy and a Sound Devices USB Pre. I am using the MLS method and I cannot get reasonable noise floor performance out of it. Some web searches revealed that the USBPre may not be suitable for MLS as the AD and DA converters are clocked individually.... Has anyone here made good MLS impulse response measurements using this kind of config? Cheers Mark Link to comment Share on other sites More sharing options...
mackerr Posted December 8, 2006 Share Posted December 8, 2006 Mark, are you measuring the response of a room, or an electo-acoustic system? I am not familiar with MLS, but I have had no problems with impulse response measurements using a USB Pre. For Smaart Live the USB Pre is pretty much the defacto standard for input devices. I also use the ESI U24 interface which is line level only, I just use the console preamps. The Smaart faq does recommend the line level inputs on the computer, but I think they meant as opposed to mic inputs on the computer. Mac Link to comment Share on other sites More sharing options...
Simon Lewis Posted December 8, 2006 Share Posted December 8, 2006 Mark, Does the USB pre work satisfactorily in dual FFT measurements ? The Maximum Length Sequence tends to 'exercise' the sound card more than the FFT measurements. Some USB sound cards have timing issues, which have been discussed on the Siasoft discussion page.Are you using the loopback function? Are you measuring the transfer function of an audio system, or the impulse response of an acoustic space? If the latter, have you tried simply using a balloon or a gun and recording the .wav file? So many questions, so little time for the fascinating world of transfer functions.... Simon Link to comment Share on other sites More sharing options...
mackerr Posted December 8, 2006 Share Posted December 8, 2006 Neither one answers your question, but there have been a couple of informative threads about Smaart on PSW this week. The first on deals with Smaart and line arrays, and the other is on Interpreting Smaart data. A couple of the participants are highly regarded system designers and techs. Let us know how your MLS project turns out. Mac Link to comment Share on other sites More sharing options...
Mark Payne Posted December 8, 2006 Author Share Posted December 8, 2006 Hi Mac and Simon I am measuring the room response. I am using a speaker system to excite the room with the MLS. Mac, MSL is a technique where an encoded sequence is played, monitored and processed (it sounds like white noise but it is carrying a coded sequence). The room impulse response is arrived at mathematically by correlating the origin sequence with the resultant measured signal. I am using this technique to capture the room response and then analyse the RT60 spectrum. I can also use the USB Pre to capture my real gun shots... no problems. She does not want to fly with MLS.... the result makes no sense. The noise floor ends up only 12db below the impulse for a start. Simon... Thanks for coming along on this. Well... yes I am using the loop back. If I use the crappy sound lappy card.. MLS works fine! When I compare the RT60s from the MLS impulse to my NTI acouslizer (interrupted pink method).... the results are similar (hey cool). The results from the gun shot impuse are around 70% longer. ..... but then my speaker system is a stack of C7... maybe directional and not eciting the room like the gun! yes this could be it... arh but the NTI meter method also used the speakers.... Bugger... and then where I place the Ld Lr and Ln markers is NOT obvious to me. Why am I doing this?... Well I have decided to compare these methods of (RT60) measurement for my IOA Diploma and I am just making sure I can get my toys working with sanity before I start testing in earnest. I would much rather push faders up........ Mark Mark, are you measuring the response of a room, or an electo-acoustic system? I am not familiar with MLS, but I have had no problems with impulse response measurements using a USB Pre. For Smaart Live the USB Pre is pretty much the defacto standard for input devices. I also use the ESI U24 interface which is line level only, I just use the console preamps. The Smaart faq does recommend the line level inputs on the computer, but I think they meant as opposed to mic inputs on the computer. Mac Link to comment Share on other sites More sharing options...
Simon Lewis Posted December 9, 2006 Share Posted December 9, 2006 If I use the crappy sound lappy card.. MLS works fine! Then use it ;-) As a single channel measurement system MLS is quite good, although swept sine seems to be increasingly popular. >>>When I compare the RT60s from the MLS impulse to my NTI acouslizer (interrupted pink method).... the results are similar. That's good to hear - it can be difficult to match different measurement platforms - even using the same techniques. I'm reading a paper that compares 5 different STIPA systems - all give different results! >>>The results from the gun shot impuse are around 70% longer. ..... but then my speaker system is a stack of C7... maybe directional and not eciting the room like the gun! yes this could be it... arh but the NTI meter method also used the speakers.... Have you got the British Standard for measuring reverberation time? If not, it's worth reading.Also, if you have a measured impulse, try the spectrograph to see if there is a difference.... >>>and then where I place the Ld Lr and Ln markers is NOT obvious to me. Strangely enough, even Siasoft weren't too forthcoming..... and it can really change your results. However, if the Acoustilyser gives you a single figure reading, do you just accept it because a figure comes up on the screen?!The manual seems to suggest placing Ld a little below the peak. >>>Why am I doing this?... Well I have decided to compare these methods of (RT60) measurement for my IOA Diploma and I am just making sure I can get my toys working with sanity before I start testing in earnest. Perfectly reasonable thing to do. In fact, any measurement technique will probably throw up more questions than answers until you understand the technique's limitations and the degree of measurement uncertainty. >>>I would much rather push faders up........ I rather like this stuff! I'm hoping to get hold of EASRA to see how that tackles RT60. I'll let you know if I can add to your data gathering. Regards. Simon Link to comment Share on other sites More sharing options...
griffter Posted December 9, 2006 Share Posted December 9, 2006 Hi Mark, Havent tried this method of measuring RT60, But as you are looking at comparing different techniquesyou may be interested to know I have had quite good results using a piece of PC Software called Room Tools.It Measured Impulse Responses and gave RT curves across different frequencies. I think Autograph Sales are the UK Distributor Regards Griff Link to comment Share on other sites More sharing options...
Mark Payne Posted December 11, 2006 Author Share Posted December 11, 2006 Thanks Griff.. I will check it out. Simon... yes I have the BS document now ...I knew I had to get the mic away from the walls and away from the direct source but... I missed pointing the speaker system into the corner of the room! Its kind of a hard thing for a sound engineer to do! It feels so wrong! Cheers Mark Link to comment Share on other sites More sharing options...
MarkPAman Posted December 20, 2006 Share Posted December 20, 2006 Talking of Smaart V6 beta 11 - Free! Link to comment Share on other sites More sharing options...
BlueShift Posted December 21, 2006 Share Posted December 21, 2006 oh and not only is it free - but its also now available for a mac. oooh and digidesign have released a core audio driver for their Mbox 2 series of USB/FW interfaces. meaning I can run protools and smaart off of the same interface. Lovely <_< Link to comment Share on other sites More sharing options...
griffter Posted December 21, 2006 Share Posted December 21, 2006 Blueshift, Wouldn't hold your breath on the Smaart Mac front! I have a new macbook pro and IMHO Smaart beta is running very sluggish on it compared to a mates PC laptop! The digi core audio drivers are known for being rather badly assembled from a coding point of view. I currently tune PA systems up using a Metric Halo MH2882 Firewire Interface and MacFOH which is still in development but runs way faster than Smaart! Regards Griff Link to comment Share on other sites More sharing options...
mackerr Posted December 21, 2006 Share Posted December 21, 2006 Wouldn't hold your breath on the Smaart Mac front! I have a new macbook pro and IMHO Smaart beta is running very sluggish on it compared to a mates PC laptop!I have been running Smaart 6 beta on my early MacBook Pro since beta 1, and while I haven't tried 6 on my Windows machine, and my Toshiba is only a single 1.6GHz P4 vs the dual 2GHz MBP, Smaart 6 on the Mac is significantly faster that Smaart 5.4 on the Toshiba. I don't see speed being an issue. I have had very good performance running Smaart, iTunes, Yamaha Studio Manager, and a couple of browsers concurrently with no noticeable performance hit. There are no glitches in iTunes while working with Smaart, SM, or browsing. Mac Link to comment Share on other sites More sharing options...
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