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The premise: bringing a second pair of loudspeakers into your auditioning room upsets the sound of the pair you're listening so badly that the first speaker's ability to correctly reproduce the timbre of musical instruments is destroyed. This observation is almost surely correct.

Defining noise is tricky business.

In high-end audio, noise is often defined as the enemy—of music, beauty, truth. Engineers and enthusiasts alike spend significant amounts of time, energy, and money attempting to minimize or control noise so that it has the least possible impact on the source signal: music. In this way—if we are intelligent, careful, and fortunate—we can extract from our stereos cleaner, clearer, more naturally beautiful sound for listening experiences that are enriching, emotionally compelling, and, above all, fun. On the other hand, when noise is allowed to excessively modulate the signal, music can sound relatively abrasive, more mechanical, and, ultimately, less engaging.

I figured it was coming, but it wasn't until just after I'd returned from the Audio Engineering Society's 2016 International Conference on Headphone Technology—held last August in Aalborg, Denmark—and was writing up my report and summary on the event for InnerFidelity.com (footnote 1) that I knew for sure: Headphones are about to change . . . a lot.

To simplify this document we have grouped the topics and set them as questions and answers either as response, tutorial or axiom. Some months ago we published a comprehensive Q&A for an online forum and to avoid repetition we occasionally refer to topics already discussed there (see [37] in the "References" sidebar).—J. Robert Stuart

MQA involves two fundamental concepts, discussed in a paper presented to the Audio Engineering Society in October 2014, the first responsible for a potential improvement in sound quality, the second responsible for a large reduction in the bandwidth required for storage and streaming of high-resolution files...