Digital filtering for detecting component frequencies from a set of predetermined frequencies

Claim 1

A numerical frequency analyzing apparatus for use in a telecommunication system comprising: means for receiving binary coded samples of voice frequency signals; and means for detecting component frequencies among each of a plurality of said frequency signals, the frequencies being detected from a predetermined number of frequencies including: a plurality of band-pass digital filters corresponding to said predetermined number of frequencies in the signals capable of being received, coupled to the output of said receiving means , means responsive to the outputs of said digital filters for determining the amount of energy in the outputs thereof, and means, responsive to said energy determining means, for selecting filters corresponding to component frequencies of each signal , the energies of which exceed a predetermined threshold level.

Claim 9

A method of analyzing samples of voice frequency signals comprising the steps of : a. simultaneously adding, in a first computing block means, the logarithms of a first quantity B2 of a band-pass digital filter provided in a plurality of band-pass digital filters corresponding to the respective different component frequencies in which useful information is contained and to which information signals are applied, a quantity Y2 corresponding to a quantity Y X - B2Y2 - B1 Y1 , which has been delayed through first and second sampling delay periods, where B1 and B2 represent first and second characteristic constant coefficients of a filter, and Y1 and Y2 represent said quantity Y which has been delayed through first and second sampling delay periods, respectively, the logarithms of said quantities Y1, Y2, B1 and B2 being stored in a plurality of accessory store elements , said first computing block means being responsive to the contents thereof in the form of logarithmic quantities, and storing an input sample X in a first register and, subsequently, converting in a first converter means, responsive to the output of said first computing block means, for converting the logarithmic quantity of said first computing block means into first linear quantities, the logarithmic sum of said output B2 and Y2 into a linear quantity B2 Y2 and storing said quantity B2 Y2 in a second register which is responsive to the output of said first converter means, during a first period of time; b. adding, in said first computing block means, the logarithm of the quantities B1 and Y1 and subtracting, in a second computing block means, which is responsive to the output of said second register, for combining said first linear quantities, the quantity B2 Y2 from the input signal sample X, simultaneously, and subsequently, converting the sum of the logarithms B1 and Y1 into a linear quantity B1 Y1 , in said first converter means, and storing said quantity B1 Y1 in said second rEgister, and storing the difference quantity X - B2 Y2 in said first register, during a second period of time; c. combining the linear quantities X - B2Y2 , and B1 Y1 in accordance with the equation Y X - B2 Y2 - B1 Y1 in said second computing block means, storing the logarithm of the quantity Y1 in one of said plurality of accessory store elements and applying the logarithm of the quantity Y2 to said first computing block means, simultaneously, and converting the logarithm of the quantity Y2 into a linear quantity in said first converter means and storing said linear quantity Y2 in said second register and, further storing in said first register said quantity Y, resulting from the combination of the linear quantities X, B2 Y2 and B1 Y1 in said second computing block means, during a third period of time; d. subtracting, in said second computing block means, the output quantity Y2 from the quantity Y, to product a difference quantity S and converting the quantity Y into logarithmic form in a second converter means which is responsive to the output of said first register, for converting the contents thereof into logarithmic form and feeding said logarithmic quantities to a second of said accessory store elements, and subsequently storing said quantity S in a third register, which is responsive to the output of said second computing block means, for storing the output of said second computing block means in linear form, and the logarithm of the quantity Y in said second of said accessory store elements, respectively during a fourth period of time; and repeating step (a) coincident with the execution of step (d).

Claim 10

A method of analyzing samples of voice frequency signals comprising the steps of : a. simultaneously adding, in a first computing block means, the logarithms of a first quantity B2 of a band-pass digital filter provided in a plurality of band-pass digital filters corresponding to the respective different component frequencies in which useful information is contained and to which information signals are applied, a quantity Y2 corresponding to a quantity Y X - B2Y2 - B1 Y1 , which has been delayed through first and second sampling delay periods, where B1 and B2 represent first and second characteristic constant coefficients of a filter, and Y1 and Y2 represent said quantity Y which has been delayed through first and second sampling delay periods, respectively, the logarithms of said quantities Y1, Y2, B1 and B2 being stored in a plurality of accessory store elements , said first computing block means being responsive to the contents thereof in the form of logarithmic quantities, and storing an input sample X in a first register and, subsequently, converting in a first converter means, responsive to the output of said first computing block means, for converting the logarithmic quantity of said first computing block means into first linear quantities, the logarithmic sum of said output B2 and Y2 into a linear quantity B2 Y2 and storing said quantity B2 Y2 in a second register which is responsive to the output of said first converter means, during a first period of time; b. adding, in said first computing block means, the logarithm of the quantities B1 and Y1 and subtracting, in a second computing block means, which is responsive to the output of said second register, for combining said first linear quantities, the quantity B2 Y2 from the input signal sample X, simultaneously, and subsequently, converting the sum of the logarithms B1 and Y1 into a linear quantity B1 Y1 , in said first converter means, and storing said quantity B1 Y1 in said second rEgister, and storing the difference quantity X - B2 Y2 in said first register, during a second period of time; c. combining the linear quantities X - B2Y2 , and B1 Y1 in accordance with the equation Y X - B2 Y2 - B1 Y1 in said second computing block means, storing the logarithm of the quantity Y1 in one of said plurality of accessory store elements and applying the logarithm of the quantity Y2 to said first computing block means, simultaneously, and converting the logarithm of the quantity Y2 into a linear quantity in said first converter means and storing said linear quantity Y2 in said second register and, further storing in said first register said quantity Y, resulting from the combination of the linear quantities X, B2 Y2 and B1 Y1 in said second computing block means, during a third period of time; d. subtracting, in said second computing block means, the output quantity Y2 from the quantity Y, to product a difference quantity S and converting the quantity Y into logarithmic form in a second converter means which is responsive to the output of said first register, for converting the contents thereof into logarithmic form and feeding said logarithmic quantities to a second of said accessory store elements, and subsequently storing said quantity S in a third register, which is responsive to the output of said second computing block means, for storing the output of said second computing block means in linear form, and the logarithm of the quantity Y in said second of said accessory store elements, respectively during a fourth period of time; and repeating step (a) coincident with the execution of step (d).