Visual acuity is the term given to the capacity to discern detail. Up to a point rods and cones function is the same manner. The are biological transducer capable of converting light waves into neural impulses. Like the eye, the ear is more than simply a biological transducer. Sound is a physical phenomenon produced by the fluctuation in air pressure.
Sounds are the results of vibrations that cause molecules to move back and forth.
As they move together they become compressed and the air pressure increases. This compression causes a vacuum that draws the compressed molecules back. The term frequency refers to the rate for vibration. The ear can detect only a limited range of frequencies. The frequencies in this range produce a sensation known as pitch.