Abstract
This chapter presents the long tradition of interest in the pages of Electronic World and Wireless World in high fidelity audio, and this of necessity includes instruments for measuring the performance of Hi-Fi amplifiers and other audio systems. Central to distortion measurements are low distortion oscillators and distortion meters. This chapter also deals with the total harmonic distortion (THD) meter that was designed based around the state variable filter (SVF). This offered ranges in a 30-10-3-1 sequence down to 0.01% FSD, permitting measurements down to 0.001% or less, although its residual noise level corresponding to 0.0009% in a 20 kHz bandwidth, 0.003% in 80 kHz, is deplorably high. It had a built-in true-rms responding indicating section using the well-known AD536 rms to DC converter. This instrument worked well and is still in use, although when making measurements at the 0.001% level one is demanding a degree of suppression of the fundamental of well in excess of 100dB, a tall order for a single notch.
Published Version
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