What is a good SNR for a medical device like a pulse oximeter?
The lower the SNR, the more flicker in a display.
So you have to determine what the USER of the measurement will expect about the accuracy of a single measurement, versus 2 measurements, versys 10 or 20 or 100.
If the measurement is 50 (average) and the peak_peak 6 sigma is +-5, then you can expect 45 to 55 as the measurement, for all but 0.0001% or 0.0002% of the time.
And 49 to 51, which is [average +- 1 sigma] or (+- 1X RMS), will be the measurement range about 60% of the time.
Which means you need to understand the bandwidth of the sensor, and how many independent measurements the sensor produces per second.
Now to your question. A SNR of 10dB for NRZ data produces a bit error about 0.1% of the time. That requires the noise to cause a deviation of 50% of the signal voltage amplitude, to make a bit error. To move +-50%, what SNR is required? 10dB (if measured in 1/2 BitRate bandwidth, 7dB if measured in BitRate bandwidth)
When you get to 20dB SNR, the probability of Bit Error is 10^-6 or 10^-8,
again for NRZ data.