Multitone Generator.vi amplitude levels

[EDGAR_PLATRONICS]

I have an audio tester system that measure audio levels of devices (microphones) we manufacture. This tester has one presicion speaker (conected  to an audio amplifier and then to a cDaq) and a referenced microphone for calibration (conected to a cDaq)

This system has worked well for 4 years but now I was requested to reduce calibration time of my system

My audio multitone calibration block is based in a multitone generator.vi provided by LV. I initially set and array 10 frequencies, 10 Levels and 10 phases

Frequencies ald 500 to 3000 hz range, phase array =0( all values), and levels are 400.

No reason why 400 but I have to start with somenting.

Then a measure level of my micropone in dBV in all frequencies and compare measurement to find worst case of level array.

Then I apply an corrective level to original array but only change that frequency. This correction was determined by experiments and it is about 15 and can be positive or negative.

Same cycle is repeated many times until measured level difference are less than 0.2 dBV 

This method is known as successive approximation.

But in some cases it takes to much time to finish

I have seen some other systems that for calibration they only do one sweept and measured signal is inverted and then aplying to the speaker to confirm calibration is flat

I want to use this method but the problem I find is multitone generator inputs I have not idea if they are percentage, voltage or what it is.

When I measure form microphone I have dBV. I have already wire dBV to the input but it does not work

See attached block diagram. I may have be missing some details but the must importat part is there.

How can I send this data to de input?

Can anyone help me ?

[EDGAR_PLATRONICS]

See attacched picture

[johnsold]

The Mutlitone Generator VI has a normalization process which may be "fighting" your calibration process. Read the detailed help file for that VI. You may want to try setting the amplitude input to the default -1. That seems to turn off the normalization.  I put together a test VI which shows the effects. Run it with amplitude set to +1. Change one of the tone ampllitudes by 0.01 and watch the measured amplitudes array and the spectrum. You will see all the amplitudes change. Try it again with amplitude = -1. Then only the amplitude of the tone for which you changed the tone amplitude input changes.

For the arbitrary values I selected for the test VI I see crest factors >3.

The rms value of the composite waveform changes very little with small changes of one tone amplitude. You might consider controlling the RMS or peak values (depending on what is most important to your tests) of the composite waveform separately from the Multitone Generator VI.

Lynn

[EDGAR_PLATRONICS]

Thank you very much

That normalization process is info I was missing.

Disabling it, will help.

Regards