Smoothed Instantaneous Loudness

Recall:

• Specific loudness is summed over frequency to obtain instantaneous loudness
• Instantaneous loudness is smoothed over time to obtain short-term or long-term loudness (time-varying)

Notes:

• Time-smoothing is nonlinear because the loudness tracks a rising amplitude more quickly than a decaying amplitude (cf. amplitude envelope followers for audio)

• Loudness of a brief sound $\isdef$ local maximum of short-term loudness

• Long-term loudness related to loudness memory over time