Frequency each pulse on sound card

Question

" I am trying enters a square sign (of encoder), the sound card filters the waves of high frequency and therefore he lacks labview information to show the perfect sign. But I believe that it is not necessary, that the sign is perfect to calculate the frequency of each pulse. Is it this way?. I alone want to know the frequency of each pulse. I don't care amplitude.
I have tried to calculate the frequency of each pulse. I have recorded the sign and once saved. I have tried to calculate counting the pulses, with the option ' indices', subtracting at the 2º -1º, 3º-2º,... .
but this is not accurate because the sample rate is to 44100 hz and I use signs from 50 hz to 10khz. To high frequency it counts very few points, to 10 khz it co
unts 4 and this is not accurate.
Is there some form of calculating it more accurate?. What vi's can I use?.
Thank you!."

Answer 1

Well, if I understand what you're saying. You are trying to read the frequency of a squarewave coming from an encoder. The problem with doing this with a DAQ card is (to put it simply) the required Nyquist samplng rate. Think for a moment, what is the frequency content of a squarewave? The fundamental (which is what you want) and a theoretically infinite number of harmonics. To adequately sample a squarewave and correctly represent the vertical edges would require an infinitely high sample rate.
If what you need is to measure the squarewave repetition rate, doing it with a DAQ card (or sound card) is the wrong way to do it. What you need is to do a pulse width measurement using a counter.
Mike...
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