Followers of an "enduring" philosophy/ MON 12-4-23 / Radio band for news and talk formats / Palindromic boy / Mineral also known as the "imperial gem" / Loose-leaf alternatives / Bygone, in Chaucer's tales / Totally reverse one's losing position

Constructor: Sean Ziebarth

Relative difficulty: Medium (solving Downs-only)

THEME: DJS (54D: Workers at dance clubs who 20-, 25-, 43- and 48-Across) — familiar phrases reimagined as things DJS do:

Theme answers:

• SET A NEW RECORD (20A: Make history at the Olympics, say)
• TURN THE TABLES (25A: Totally reverse one's losing position)
• MOVE THE NEEDLE (43A: Have an impact that can be gauged)
• DON'T MISS A BEAT (48A: Keep going without faltering one bit)

Word of the Day: AM STEREO (4D: Radio band for news and talk formats) —

AM stereo is a term given to a series of mutually incompatible techniques for radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers. There are two main classes of systems: independent sideband (ISB) systems, promoted principally by American broadcast engineer Leonard R. Kahn; and quadrature amplitude modulation (QAM) multiplexing systems (conceptually closer to FM stereo).

Initially adopted by many commercial AM broadcasters in the mid to late 1980s, AM stereo broadcasting soon began to decline due to a lack of receivers (most "AM/FM stereo" radios only receive in stereo on FM), a growing exodus of music broadcasters to FM, concentration of ownership of the few remaining stations in the hands of large corporations and the removal of music from AM stations in favor of news/talk or sports broadcasting. By 2001, most of the former AM stereo broadcasters were no longer stereo or had left the AM band entirely. [...] 

Globally, interest in and use of AM stereo has been declining steadily since the 1990s, as many music stations have continued to move to the FM band. As a result, the vast majority of AM stations broadcast news/talk or sports/sports talk formats. Many of the stations that initially implemented AM stereo are clear-channel 50,000-watt stations, and are more concerned with listening range than stereo sound (although there is no proof that use of AM stereo affects listening range). As a result, these stations still have the necessary equipment to broadcast in stereo, but it is left unused (or converted to HD Radio). Also, many former AM stereo stations were bought up by broadcasting conglomerates, which generally discourage AM stereo broadcasting. In the United States, most stations currently using AM stereo are small, independently owned and broadcast a variety of music format. (wikipedia) (emph. mine)

It's Monday, so why (oh why) would you burn one of the very few longer non-theme answers you have on a weird, semi-defunct non-thing like AM STEREO? I just don't get it. Did you software insist? It's only the second time the answer has ever appeared in the NYTXW, and for a reason. Just read the "Word of the Day" entry, above. It's not a (widely used) thing. It was supposed to be, but then ... no. AM RADIO, that is a thing, use that answer any time you like, but AM STEREO!? Woof and oof and Please Care More About The Answers You Put In Your Grid. If they aren't familiar or known, to say nothing of beloved, to you, then Don't Use Them, no matter if your wordlist is telling you the answers are valid or not. This is not (not not) a demanding grid, thematically. That is, the theme is basic, only four answers, and is therefore not putting a ton of pressure on the rest of the grid. So why, given the various ways you could've arranged the themers, placed the black squares, etc., did you decide on AM STEREO? Again, you don't have many longer answers to work with, and ... AM STEREO? These longer answers are the ones you would lock down first, right after you'd placed the themers. In fact, *whether* you could lock down *good* longer answers would (or should) play a significant role in where you put your themers in the first place. NODDED AT is not exactly making up for AM STEREO. After that, only LASAGNA and TEABAGS come in at even seven letters. Most of this grid is 3-4-5 (black square count is a robust 44, making the grid pretty choppy and short answer-laden). You *gotta* care about more than just the theme. And if your Spidey-Sense gives you even a hint of "Is that a thing?," then you know the answer: scrap it. I realize AM STEREO is not going to infuriate that many people because it's Monday and the puzzle is easy and who cares. Well, now you know who cares.