PCM1840: Question on DR Parameter

Hi,

They are similar specs, which is why the numbers are so close, but we measure them differently.

SNR is measured by grounding the ADC inputs to 0. The resulting digital output from the ADC will be the effective noise floor of the ADC. SNR by definition would be 0dB - [Noise Floor] so the SNR is the same number as the measured output in dBFS (dB full scale).

DR (Dynamic Range) is measured by applying a -60dB signal to the ADC and taking a THD+N result of the output. The input signal is so low that no additional harmonics are created. This reduces the THD+N measurement to be equivalent to an SNR measurement with a -60dB input. By adding 60dB to the result (in magnitude) this gives dynamic range. 

The SNR is focused on measuring the noise floor of the ADC, similar to an idle channel noise measurement.

The DR is focused on measuring the difference between the loudest signal possible and the smallest signal possible (noise floor).