Example:
Dots are sample values.
Three instances of 12kHz tone samples at 48kHz sample rate, and one at 11239Hz (a prime number near 12000)
First exercises 2 sample values plus zero
Second exercises 4 sample values
Third only exercises 2 sample values.
Last probably hits them all (maybe not every one of the combinations, but probably each of the 16 or 24 levels that contribute to the data->voltage conversion)
View attachment 8047
Seems to me like you'd want to exercise all (16 or 24) of the sample bits as a linearity check.