Modifying a White Noise Machine for Lower Frequency Sound

Who knew? Apparently the HoMedics Deep Sleep Mini Portable Sleep Sound Machine white noise machine, model HDS-055-BL (not sponsored), is just a fancy MP3 player!
This is a nice little white noise machine, but its tone tends to have enough high frequencies that with prolonged use my ears start ringing, even with the Brown noise setting and the tone control all the way to bass. The goal of this project was to modify the sound machine to filter out some of the high frequencies, which I was planning on doing using an RC/LC low-pass filter network. But it turns out that the audio for the different settings comes from MP3 files on a Micro SD card, so it's actually easier to just change the files it plays. Which means you can also load different sounds onto it - for example, the sound of a steam train.
This thing is way more flexible than I had even imagined!