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Dual Channel FFT
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<blockquote data-quote="Mark DeArman" data-source="post: 56111" data-attributes="member: 950"><p>Re: Dual Channel FFT</p><p></p><p></p><p></p><p>Well I see how this is easily met with COTS products since channel pairs are normally implemented with a stereo ADC.</p><p></p><p></p><p></p><p>Strange, the extra propagation delay must be a behavior inherent to Smaart. In fact there should be more usable bandwidth available as the reference is already stored in memory. I don't see how a system designed to work as I described would suffer from extra propagation delay or clock synchronization issues after calibration measurements had been made. (Assuming the hardware is not restarted.) Although, I would agree that Windows or other OS synchronization issues might be a real problem with low-end drivers.</p><p></p><p></p><p></p><p>I don't see how a typical dual channel FFT differs in this respect. If you are taking your loopback input off of one interface that tells you nothing about the second interface. If as I proposed in the previous post you took calibration measurements of each input against the output then those would be correct. (At least until you restart the hardware that is; assuming no ref clock or sync pulse between interfaces.)</p><p></p><p></p><p></p><p>Would it not be better to make a calibration curve even perhaps from the amplifier output if you are concerned about issues in the signal path?</p><p></p><p>From <span style="color: #3E3E3E">Langston Holland's post I believe point (2) </span><span style="color: #3E3E3E">is the most important reason COTS measurement systems are implemented as dual channel FFT. This value can be as high as 100ms on low end hardware which would be bad for any type of transfer function measurement (even a std dev<1ms is not good.) For ASIO I have seen histograms which are close enough to real-time (i.e. hardware designed with ref clock, sync pulse and trigger pulse) for audio work.</span></p><p><span style="color: #3E3E3E"></span></p><p><span style="color: #3E3E3E">I would appreciate any other thoughts on the subject.</span></p><p><span style="color: #3E3E3E"></span></p><p><span style="color: #3E3E3E">Mark DeArman</span></p></blockquote><p></p>
[QUOTE="Mark DeArman, post: 56111, member: 950"] Re: Dual Channel FFT Well I see how this is easily met with COTS products since channel pairs are normally implemented with a stereo ADC. Strange, the extra propagation delay must be a behavior inherent to Smaart. In fact there should be more usable bandwidth available as the reference is already stored in memory. I don't see how a system designed to work as I described would suffer from extra propagation delay or clock synchronization issues after calibration measurements had been made. (Assuming the hardware is not restarted.) Although, I would agree that Windows or other OS synchronization issues might be a real problem with low-end drivers. I don't see how a typical dual channel FFT differs in this respect. If you are taking your loopback input off of one interface that tells you nothing about the second interface. If as I proposed in the previous post you took calibration measurements of each input against the output then those would be correct. (At least until you restart the hardware that is; assuming no ref clock or sync pulse between interfaces.) Would it not be better to make a calibration curve even perhaps from the amplifier output if you are concerned about issues in the signal path? From [COLOR=#3E3E3E]Langston Holland's post I believe point (2) [/COLOR][COLOR=#3E3E3E]is the most important reason COTS measurement systems are implemented as dual channel FFT. This value can be as high as 100ms on low end hardware which would be bad for any type of transfer function measurement (even a std dev<1ms is not good.) For ASIO I have seen histograms which are close enough to real-time (i.e. hardware designed with ref clock, sync pulse and trigger pulse) for audio work. I would appreciate any other thoughts on the subject. Mark DeArman[/COLOR] [/QUOTE]
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