Method and apparatus for determining a masked threshold

Apparatus for determining a masked threshold curve as a function of frequency from a magnitude spectrum as a function of frequency, the magnitude spectrum being in the form of magnitude values for a number of subsequent frequency values in a frequency range of interest, the apparatus comprising

• a terminal for receiving said magnitude values for said number of subsequent frequency values,
• first means for determining for each frequency value a first masking component at said frequency value resulting from a frequency component at said frequency value and having a magnitude equal to the magnitude value of the magnitude spectrum at said frequency value,
• second means for determining for subsequent frequency values when going in one direction through the frequency range of interest a second masking component at a frequency value, the second masking component for said frequency value being determined from the first masking component and the second masking component at only the frequency value directly preceding said frequency value, said second means comprising memory means for storing at least one masking component for each of the frequency values,
• third means for determining for subsequent frequency values when going in the reverse direction through the frequency range of interest a third masking component at a frequency value, the third masking component for said frequency value being determined from masking information that has a relation to at least the first masking component and the third masking component at only the frequency value directly preceding said frequency value,
• fourth means for determining a masked value for each frequency value in said masked threshold curve from masking information that has a relation to said first, second and third masking components (if present) for said frequency value.