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I use this device in consumer level system without any S/N ratio or dynamic range problems
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Well, I can only look at specs and make suggestions, so I have to defer to what you say, since I don't own a 2496.
But, as I'm sure you know, the LSB (least significant bit) voltage is directly proportional to the maximum input full scale voltage. In this case it's +/-9.75 volts RMS. So, if the input level isn't high enough, the LSB will not be distinguishable from the noise. The noise floor for the ADC converter is fixed and a function of the bit resolution, which in this case is 24bits. It has a theoretical noise floor of 147dB.
Well, of course the device can't obtain that figure, but it does show an incredible noise floor spec of 112dB in relation to full scale of 22dBu. That's extremely good (almost unbelievable actually
). Well, 112dB translates to about 18.5 bits usable above the noise. Quite good.
This all assumes you have a full scale input signal with a swing of +/- 9.75 volts. As you decrease the input signal, the noise rises exponentially. It's the nature of the math. A full scale of 1.25 volts is only about 13% of the possible full scale allowed. I won't bore anyone with the math, but this translates to about 4 bits being used with a dynamic range of about 24dB. That's horrible.
What can I say.
brucek