Amplitude

The Amplitude Is the Height of the crust in a sound wave and it affects the loudness of the sound, loudness of sound can be harmful if crossed the limits.

Db in SOUND

Amplitude or loudness of sound is measured in db (Decibels). Decibel is not an absolute scale, it is a relative scale, it is only used for measuring ratios, and that depends upon different situations. But there is no answer that what exactly is 1db as we know in kg or km.

Therefore these Assumptions come into play, which are different for real sound and audio.

When we talk about the Real sound, in order to measure loudness of sound, a level of the minimum sound (threshold) which is pure silence is set to be 0 db. And with that reference we can measure the loudness of the real sound in reality as we go up by 5db 10db 15db and so on. With these measurements it is assumed that loudness within 100db is safest sound that is audible. Maybe 115 db can be harmful.

Db in Audio

Now for Audio, It Is totally reversed, when we talk about decibels in audio 0db is the maximum value that any audio device can handle. And then all audio is based on negative values of decibels.  That is 0db, -5db, -10db, -15db.                                                                                                     

                             Max, loud, less loud, lesser loud and so on.