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With smaart why do I have to loop back the output to my input?

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Carl Townshend:
Hi all
With smaart why do I have to loop back the output to my input?
When I want to do a phase measurement do I need this loopback?

Doug Fowler:

--- Quote from: Carl_t on January 18, 2021, 04:16:28 pm ---Hi all
With smaart why do I have to loop back the output to my input?
When I want to do a phase measurement do I need this loopback?

--- End quote ---

Read the rules, fix your display name.

Thank you for your cooperation. 

Luke Geis:
Yes, it's how Smaart compares the data sent vs. the data received. If Smaart doesn't receive a signal back via the measurement mic, it will have no data to show you the phase relationship, spectral information of FFT data.

Corey Scogin:
Comparing the measurement signal to a theoretical digital signal reference means the interface output and input are part of the measured system.
Comparing the direct electrical signal reference with the measurement signal reference takes the interface I/O out of the equation allowing Smaart to measure only the external system you want to measure.

When using 1-input mode (no electrical reference), Smaart is assuming the interface frequency and phase response are flat.

The reference signal also helps measure delay which is required for phase measurements. Smaart doesn't necessarily know the delay inherent in your interface's digital-to-analog and analog-to-digital converters. Comparing against the reference signal loop allows it to compensate for that delay accurately.

That's my understanding anyway. Others can add or correct me.

Mark Wilkinson:

--- Quote from: Carl Townshend on January 18, 2021, 04:16:28 pm ---Hi all
With smaart why do I have to loop back the output to my input?
When I want to do a phase measurement do I need this loopback?

--- End quote ---

hi Carl,

You don't necessarily have to loopback output to input to make a transfer function measurement.

The first thing to understand about a transfer function is that it is a comparison of Signal A, to Signal B.
These two signals can come from many places:  Smaart's internal signal generator, a line out of a mixer or processor, a microphone,..... just to name a few.

Doesn't matter, it's always just a comparison of A (reference channel) to B (measurement channel)


If you decide to use Smaart's signal generator output as the Reference signal,  you need to send the Signal Generator's output  to the Reference Channel input.
This is where loopback comes in: it's just an easy way to do that right at the soundcard.

Alternatively, you could send the Signal Generator's output to a mixer without using a loopback (at the soundcard).
And send an output from the mixer back to the soundcard's Reference Ch. input. 
Accomplishes the same thing as loopback.


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