This blog post's title is a bit of a stretch! For starters, I almost exclusively use FLAC audio files for my primary music store, so my need to be able to handle other audio formats is not exactly great. Still less do I need to handle so many different audio formats that you could describe a tool that handles them all as truly 'universal'!
But I do have need to create MP3 copies of my FLAC music files -because I upload them to OneDrive and am able to play them from there on my phone. If I'm listening to music on my phone, it means I am visiting family, staying in a hotel, at an airport or on a train: so the loss of audio 'fidelity' inherent in the transition from lossless FLAC to lossy MP3 is tolerable. Those environments are not suitable for audiophile ears at the best of times!
I also occasionally buy CDs or audio downloads in assorted "High Definition" formats. Basically, these will be FLAC files encoded using 24-bit depth and sampling rates north of 88.2KHz, rather than the 'traditional' CD's 16-bit depth and 44.1KHz sampling rates. The extra bits and higher sampling rates is supposed to make these High Definition audio formats sound better than ye ancient stereo CDs... but my ears cannot hear the difference. Meanwhile, the HighDef files are 8 or more times the size of what you'd usually get on a standard CD. Why store 8 times as much data whose audio 'improvements' you can't actually hear?! So, sometimes, I need to convert from high-def FLAC to standard-FLAC. (You can legitimately ask, too, why I'd pay more for a High-Def version than a standard CD, but that's usually the result of me making a mistake on the music vendor's website!)
I had an enormous library of little scripts that would do the various conversions, created over time as occasion demanded each new variation. They aren't hard to come by on the Internet, after all. But invoking different scripts depending on specific circumstances was getting a bit tedious -so I wanted a single tool that was conveniently run-able and would handle all my audio conversion needs: FLAC-to-MP3; FLAC-to-FLAC; the occasional APE-to-FLAC; the rarer FLAC-to-OGG and the even vanishingly rarer SACD-ISO-to-ordinary-FLAC. The result is the Absolutely Baching Universal Audio Converter or AUAC to its friends.
As ever in this part of the woods, the 'program' is really just a Bash script, downloadable from here. You install it, plus a bunch of dependencies (mainly ffmpeg). And then you can visit a directory full of audio files in a terminal session and do things like auac -o=ogg (meaning convert FLACs to OGG) or auac -i=iso -o=flac -d=y (meaning 'decode my SACD ISO into FLAC files and then delete the source ISO when you're finished). It works in parallel fashion, so multiple files are converted at once, rather than one after another: it's accordingly reasonably fast. It's simple to invoke at a Linux command line and it's now my daily driver for keeping my MP3 collection in synch with my master FLAC collection.
It isn't, therefore, truly 'universal', in that it's not able to cope with every audio format known to man (basically: flac, ogg, mp3, ape, wav, iso and wma are covered, but nothing else is). But it's available to anyone that wants it, for nothing, and there's a full-length article available over in the Technical section which acts, basically, as its manual.