Signal transforming device

The signal transforming device 10 is suitable, inter alia, for producing a Fourier transform. A clock- activated counter 16 selects a cosine function and a sine function value at each of a set of frequencies. The function values are stored in a counter-addressed memory 22. Each value is multiplied in a respective multiplier 20R,20I by a signal sample from buffer 12. The products are added to the contents of respective registers 30R and 30I, in which products involving each function are added to the contents of a respective location. A further signal sample is multiplied by a further value of each of the functions and augments register contents. The register contents are constrained to decay by the application of a decrement factor implemented by memories 28R and 28I. The result is that the invention simulates a bank of filters each with bandwidth governed by the decrement factor and centre frequency set by the corresponding stored function. The invention may be arranged for individual filter centre frequency agility and/or individual filter bandwidth agility. It generalises to arbitrary filters or functions, and provides an elegantly simple means for decomposing a signal into a set of functions and corresponding amplitude coefficients.