I feel like the Twitter thread—for all its focus on royalty math—is missing some crucial context for people not immersed in the sausage-making of audiobooks, specifically Audible's ACX platform. I worked for Audible some years ago, so understand this context a bit better than most, and can explain for those who are interested. I left Audible not too long after ACX launched, but remember many meetings about it. To be fair, though, I was not directly involved in the creation of ACX and my recollection of its details are fuzzy.

The thread author's complaint about Audible relates specifically to ACX. Again, even if you are an avid AB listener, you are probably not aware of the existence of ACX because its function is extremely boring. It's Audible's "audiobook rights marketplace". It is designed especially for people that hold the rights to books that would otherwise not be produced in audio. Those people can use the ACX platform to connect with narrators and producers who will help them record an audiobook version of their text, which will eventually be distributed on Audible—and therefore Amazon and (the holy grail) iTunes.

If you're Stephen King, then Simon & Schuster is your publisher in hardcover, paperback, ebook, audio, whatever. There is no doubt in anyone's mind that Stephen King's next novel will be made into an audiobook, and it will release the same day in every format imaginable. The Stephen Kings of the [audio]book world will have never have anything to do with ACX. No need.

On the other hand, if you're a low-to-mid-tier author published by a smaller house that doesn't have audiobook production capabilities, things get dicier. Before Audible, many, many, many books were never made into audiobooks. Audiobook production is time-consuming and expensive, and audiobooks were a niche format. Audiobook rights, therefore were often sold to audiobook-only publishing houses that don't hold quite the same prestige as names like Random House or Penguin. You've probably never heard of these publishing houses, except maybe at the beginning of an audiobook: "Blackstone Audio presents…", "Brilliance Audio presents…", "Recorded Books Presents", etc. Those audiobook-only publishing houses could pick up the rights to reasonably well-known books and authors that their print publisher had no intention of producing in audio.

Now that audiobooks have become much, much more mainstream—in no small part thanks to Audible's efforts—there are fewer scraps from the major publishers to fight over. Today there is a much greater likelihood that a print book will be published in unabridged audio than there was twenty years ago. But there are still many "lost" books that didn't get picked up by the major audiobook publishing houses. Or the mid-tier ones, or even the bottom feeders. That's where ACX comes in.

If you must use ACX to publish your audiobook, it's been overlooked (perhaps unfairly) by just about everyone else who could stand to make a buck off of purchasing the audio rights and producing it. Perhaps there is a more charitable way to put it, but that's the gist.

Using ACX is definitely a gamble. It's a gamble for everyone except Audible. The gamble is this: you will spend thousands of dollars producing an audiobook. In exchange you will get distribution on the biggest audiobook marketplaces in the world: Audible, Amazon, iTunes. As I recall, there were ways to split this risk. If a narrator/producer believed that the audiobook would be a best-seller, they could negotiate a lower upfront fee in exchange for a cut of back-end sales, for example.

The specific terms of the ACX deal you sign on for are certainly in Audible's favor. The only way to get better terms is to have your audiobook rights picked up by a major publishing house that has a deal in place with Audible already. Then you are largely shielded from all of these details by your publisher/manager/lawyer. If you're on ACX, it's likely because you have no other choice. Audible's fee here is largely just a way to gatekeep access to their huge distribution platforms: the Audible service itself, Amazon, and iTunes.

I can't speak to the specifics of the author's complaints about how royalties are calculated. But knowing the people that worked, and still work at Audible, my gut feeling is that there is no malicious intent here. At worst, there is an imbalance of emotional investment between the authors and Audible. These authors have, after all, likely spent years of their life working on a book and shepherding it through the publishing world themselves without the aid of a publishing house. Audible, on the other hand, is largely devoted to the content they publish, the Audible platform itself, and their goal of converting people into subscribers.