You can get some ADC and DAC cards for measurement use at low data rates at more than 24bits, and you can obviously integrate an external DVM via say IEEE-488. I used to do 81/2 (about digit measurements using an HP3458, but only at 50 readings per second.
Not many signals have more than 24bits of dynamic range in an audio bandwidth - If you have something that is 1V full scale, and you manage a noise floor of 1nV/rtHz you are doing really well, but in a bandwidth of 100kHz, this corresponds to 300nV of noise per sample, so your S/N is about 3,000,000:1, and 24bit data (16,000,000:1) is measuring several bits of noise. If you can keep the same noise floor in a system that is CD level (2V RMS full scale) you are just clear of being Johnson noise limited.
Note that if you don't need full audio bandwidth, you can digitally filter the 24bit data to get extra resolution. This can give several extra bits, if the converter linearity is good enough to make them useful.
Not many signals have more than 24bits of dynamic range in an audio bandwidth - If you have something that is 1V full scale, and you manage a noise floor of 1nV/rtHz you are doing really well, but in a bandwidth of 100kHz, this corresponds to 300nV of noise per sample, so your S/N is about 3,000,000:1, and 24bit data (16,000,000:1) is measuring several bits of noise. If you can keep the same noise floor in a system that is CD level (2V RMS full scale) you are just clear of being Johnson noise limited.
Note that if you don't need full audio bandwidth, you can digitally filter the 24bit data to get extra resolution. This can give several extra bits, if the converter linearity is good enough to make them useful.
I doubt if there's a genuine monotonic 1/2LSB accurate 24 bit ADC anywhere. Many ADCs produce 24 bits of data but that doesn't mean they're all accurate. Most IC ADCs these days are 1 bit noise-shaped devices that quote "A" weighted S/N ratios with continuous signals; this is very different from a true 24 bit accurate ADC.
To sum up, you can't even get a true 24 bit ADC, certainly not on a soundcard, so forget > 24 bit.
To sum up, you can't even get a true 24 bit ADC, certainly not on a soundcard, so forget > 24 bit.
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