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.