Testing audio fidelity with absolute dynamic range

As more and more consumer products are embracing the innate benefits of digital audio amplifiers, the demand is increasing for better and better audio fidelity at increasingly lower cost. Unfortunately, credible metrics for assessing and comparing audio fidelity price performance amongst digital amplifiers are not well defined. The traditional metrics in use today like Total Harmonic Distortion plus Noise (THD+N) and Signal to Noise (SNR), both of which are necessary attributes for good audio, have not proven to be good predictors of high fidelity for digital amplifiers, and none truly assess the ability to faithfully reproduce very small audio signals. The ability to reproduce silence or small sounds is every bit, if not more, as important to the overall sonic experience as is the ability to create loud sounds.

For example, the sonic experience is much warmer, clearer and crisper with the amplifier capable of reproducing a signal 100dB down from full scale (100dBFS) compared to the one capable of only 85dBFS. This range of linearity, referred to as Absolute Dynamic Range (ADR) and measured by a Deviation from Absolute Linearity (DAL) test, is an important, credible metric of fidelity for digital amplifiers by indicating ability to accurately reproduce the low level tones and harmonics that give audio its richness, detail, and clarity. The DAL test determines at what input signal levels the output amplitude deviates from absolute linearity relative to the input and can no longer faithfully track the input. As a demanding test traditionally used for characterizing high performance audio digital-to-analog conversion systems, it typically will reveal problems at much lower input signal amplitudes than the standard -60dBFS probe tone test.