Patent ID: 7563975

Claim:
A tone correction system comprising: a music module configured to receive an analog signal and including command inputs; and a computer, responsive and operably connected to the music module, including; a processor; memory including commands and reference frequency values; and a digital signal processor; the computer configured to: create a time series of values from the received analog signal; select a subset of the time series of values as a frame; input the frame values to a difference function d ′ ⁡ ( τ ) = ∑ W - r 1 ⁢ ( x j - x j + τ ) 2 2 ⁢ ∑ W - r 1 ⁢ ( x j 2 - x j + τ 2 ) . where W is the number of values in the frame and χ j is a value in the frame and τ is a variable representing a time delay; select a plurality of function minima values corresponding to frame frequencies from the difference function results; and determine a frame fundamental frequency from the selected minima values using a first aperiodicity threshold value and a first temporal threshold value.