Jim Austin

I mention this because the HomePod's "smart" features—its integration with Siri and the Apple Music streaming service—is a big part of its appeal. In its natural element, the HomePod provides a way of accessing music that, although as old as our century, to me is still new and unfamiliar: Forget your hoary music collection, your Rolling Stones and Beethoven. Decide what kind of music you want to hear—a genre or a mood—then leave the choice to Siri and her algorithmic minions.

I'm sitting in a rented Nissan just off Highway 61—yes, that Highway 61—looking out at a Shell station through the bug-stained windshield and across a litter-strewn, not-yet-planted cotton field. It's late March, and I've just left Clarksdale, Mississippi, on my way to Memphis. Leaving Clarksdale made me thoughtful, so I've pulled over to jot down a few notes.

The sampling theory formulated by Claude Shannon in the late 1940s had a key requirement: The signal to be sampled must be band-limited—that is, it must have an absolute upper-frequency limit. With that single constraint, Shannon's work yields a remarkable result: If you sample at twice that rate—two samples per period for the highest frequency the signal contains—you can reproduce that signal perfectly. Perfectly. That result set the foundation for digital audio, right up to the present. Cue the music.

Master Quality Authenticated (MQA), the audio codec from industry veterans Bob Stuart and Peter Craven, rests on two pillars: improved time-domain behavior, which is said to improve sound quality and what MQA Ltd. calls "audio origami," which yields reduced file size (for downloads) and data rate (for streaming). Last month I took a first peek at those time-domain issues, examining the impulse response of MQA's "upsampling renderer," the output side of this analog-to-analog system (footnote 1). This month I take a first look at the second pillar: MQA's approach to data-rate reduction. In particular, I'll consider critics' claims that MQA is a "lossy" codec.