The following intervals are all minor seconds because the two notes are directly next to each other in the chromatic scale. On the piano keyboard, these pitches are played by keys that are next to each other.
A minor second is also known as a half step, which is used to determine the quality of any interval. A half step is the smallest interval in Western music and the octave is divided into 12 half steps.
The chromatic scale is a scale consisting of all half steps. The prefix chroma- means color, which appropriately describes a scale of half steps, which uses every pitch (or musical color) available.
Noteworthy: Musicians in India use microtones to create slightly sharp or slightly flat variations of half steps. This means that Indian music (unlike Western music) uses intervals that are smaller than the half step.
Counting Half Steps
Counting half steps differs from counting the numeric portion of the interval. The number of half steps in a given interval is counted using the same method you would use to count steps that you take with your feet. If you start with your feet together and want to move 4 steps forward, you begin counting when you place one foot in front of the other – that is your first step (i.e., you do not count the standing position as one).
Likewise, when you count half steps, the first half step occurs when the distance of a half step has been travelled.
So, C to Db is a minor second because I count C as 1and D as 2 to find the numeric portion of the interval. C to Db is 1 half step because the distance between C and Db is a single half step.