A graph of the quietest sound you can hear at each frequency, plotted in decibels of hearing level (dB HL) against frequency in Hertz. It is the cornerstone of any hearing assessment. Audiologists test you in a sound-treated booth from roughly 250 Hz to 8 kHz, sometimes higher. A dip on the right of the chart is the classic noise-induced or age-related pattern, and it is the dip most often associated with tinnitus.