Digital realisation of phono (RIAA) equalisers

The author presents a digital realization of phono equalizers, using a simple first-order analog pre-emphasis filter combined with a digital IIR (infinite impulse response) type filter. This approach makes it possible to use a relatively simple digital filter to achieve an accurate frequency response and a good dynamic range. Computations show that a relatively simple second-order digital filter in combination with a first-order analog filter yields a response accuracy practically unobtainable with conventional phono equalizers, especially when the influence of component tolerances, temperature, etc. is taken into account. Achieving good noise and distortion properties in the digital equalizer is easy, and the analog stage is much simpler than in conventional completely analog equalizers