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synchronisation of FFT Blocks / Tech Note on page 67 of UM
PostPosted: Wed Apr 01, 2015 12:37 pm Reply with quote
Lars
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Joined: 31 Mar 2015
Posts: 5




Hey there,


this question is about the tec note on page 67 of the systune manual, the general topic is the deconvolution concept / inverse FFT Blocks and the importance of the synchronisation of the FFT Block fromm input and output of the SUT. I fully understand why it is important that these blocks must be synchronized (increasing delay / unsynchronity between the blocks means decreasing correlation). So far so good. What I donīt quite get is the point where itīs mentioned in the bottom of that Tec Note that the process of synchronizing the blocks in Systune is easy and how itīs made.

Quote:

"It is obvious that for maximal measuring accuracy the actual delay must be found in order to adjust the two channels against each other time-wise. Only then, the FFT blocks for signal and reference will be optimally correlated. In SysTune this is a very simple process: First you usually measure with a long FFT size in order to determine the delay. This value can then be entered for any subsequent measurements, whether it is with longer or shorter FFT size. This ensures synchronicity of FFT blocks from input and output."


Hereīs my question:
Is this pointing to the compensation of the delay offset or is this pointing out the general importance of finding and adjusting the delay times between different system components? As far as I understand this I would say it points to finding and compensating the elektronical delay via the delay offset, is that correct? How do I do this correctly in order to increase the accurancy of my measurements? Is it of any importance to adjust the FFT Block size after the compensation and if it is, what is the smartest way to do that?

Sorry for my english and thanks in advance!

Best regards,


Lars
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PostPosted: Thu Apr 02, 2015 12:03 am Reply with quote
Lars
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Joined: 31 Mar 2015
Posts: 5




Laughing In the german language we have a saying that unfortunately is rather impossible to translate into english without turning to "denglish" wich would be a classical mixture of both languages...

Never the less: " He who can read is in clear advantage!"

--> if you keep on reading the freakin manual a few pages further, possibly a lot of questions will find their answers...
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PostPosted: Mon Apr 06, 2015 12:31 am Reply with quote
AFMG Pedro Lima
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Joined: 05 Jun 2010
Posts: 234
Location: Brazil




Hi Lars,

That's related to the measurement delay, yes. And not between speaker components.

To compensate for it, start measuring until you see a stable Impulse Response. Then, just press PEAK button in the Input section to the left (an maybe RESET the averages). You will see the Impulse Response peak going to 0ms.

In practice you can actually have a offset of about 20% of the FFT size. This is fine in SysTune, differently from other software products, since what you see is the full RIR.

Hope that helps,
Pedro Lima
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synchronisation of FFT Blocks / Tech Note on page 67 of UM
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