Signal Noise Reduction

A noise reduction method comprising:

• a first rank calculating step for calculating a rank for each element included in a first region, depending on a value of the element, the first region having predetermined sizes in the time axis direction and in the frequency axis direction in a noise section of an observed signal indicating variation of a frequency spectrum with time;
• a second rank calculating step for calculating a rank for each element included in a second region, depending on a value of the element, the second region having predetermined sizes in the time axis direction and in the frequency axis direction in the observed signal;
• and
• a subtraction step for subtracting, from values of the respective elements in the second region, values based on values of the respective elements in the first region whose ranks correspond to those of the elements in the second region.

An article of manufacture comprising a computer usable medium having computer readable program code means embodied therein for causing noise reduction, the computer readable program code means in said article of manufacture comprising computer readable program code means for causing a computer to effect the steps of:

• a first rank calculating step for calculating a rank for each element included in a first region, depending on a value of the element, the first region having predetermined sizes in the time axis direction and in the frequency axis direction in a noise section of an observed signal indicating variation of a frequency spectrum with time;
• a second rank calculating step for calculating a rank for each element included in a second region, depending on a value of the element, the second region having predetermined sizes in the time axis direction and in the frequency axis direction in the observed signal;
• and
• a subtraction step for subtracting, from values of the respective elements in the second region, values based on values of the respective elements in the first region whose ranks correspond to those of the elements in the second region.