Audio Precision: Cabot, Fundamentals of Modern Audio Measurement

by Richard Cabot, Audio Precision

Fundamental concepts in testing audio equipment are reviewed, beginning with an ex- amination of the various equipment architectures in common use. Several basic ana- log and digital audio measurements are described. Tradeoffs inherent in the various approaches, the technologies used, and their limitations are discussed. Novel tech- niques employing multitone signals for fast audio measurements are examined and ap- plications of sampling frequency correction technology to this and conventional FFT measurements are covered. Synchronous averaging of FFTs and the subsequent noise reduction are demonstrated. The need for simultaneity of digital and analog generation is presented using converter measurements as an example.

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Characterizing professional and consumer audio equipment requires techniques which often differ from those used to characterize other types of equipment. Sometimes this is due to the higher performance requirements.

Other times it is due to the peculiarities of the audio industry. Other fields deal with some of the same measurements as those in audio. From level and THD to jitter and noise modulation, no other field has the breadth of requirements found in high performance audio. Performing these measurements requires a knowledge of the tradeoffs inherent in the various approaches, the technologies used, and their limitations. We will examine these measurements and their use in practical engineering and production applications. Audio has been an analog world for most of its life. The last 15 years have seen a steady increase in the use of digital technology, including the digital recorder, digital effects units, the compact disc, digital mixing consoles and lossy data compression systems. Each has necessitated its own collection of new measurements for the new problems introduced.