The HN post made the front page and got me the most traffic and feedback I'd had so far (about 6k visitors). It also resulted in articles on BoingBoing and Metalfloss, among others, which also sent a decent number of users.
The 1440 newsletter [2] also picked it up - just a small one-liner in a list of interesting links - and sent about 8k visitors in one day.
On Twitter it got picked up, unexpectedly by quite a lot of DJs. Turns out that a lot of DJs get tinnitus and white noise can be really helpful to mask it. So I got much less traffic from that but some really nice feedback on how useful it is. That also led to The Economist's podcast team contacting me and I ended up featuring in a piece about ambient music and white noise apps.
I did try ProductHunt and it got nowhere. It probably didn't help that I didn't really promote the launch, but it also got buried under a lot of AI projects. Ho hum.
User numbers have stabilised now at about 600-800 a day. I'm not really sure where to turn next - I hate constantly banging on about it on my personal Twitter and reposts of things that have got traction are discouraged on HN and Reddit (rightly so). I'm happy that it's got a decent userbase though.
[0]: https://ambiph.one
[1]: https://news.ycombinator.com/item?id=38856999
[2]: https://join1440.com/newsletter/florida-drug-imports-starsky...