AudioNodes is a complex application that needs to interface with your system in dozens of ways: it needs to output audio to your speakers or headset, obtain input from your microphone, drive complex graphics computations, and so on. On the Web, this is made possible by your browser, which allows web-applications (such as AudioNodes Online) to access these technologies.
Right now, your browser is missing some of these technologies that AudioNodes Online requires to function correctly.
If you are using Chrome, Firefox, or Edge, we'll go ahead of things and simply recommend you search for this exact question in your favorite search engine and pick the result you like most (search results for Google, Bing).
If you are not, the official site for each of our recommended browsers will have everything you need to get going, and they'll explain it better than we could.
AudioNodes Online does not display this message based on browser name or version. For all it cares, you could be using a custom self-built browser. Instead, it runs some tests to see if the needed technologies are there (and work as they should). If something is missing, you'll get this message, and this is exactly what happened now.
It is possible that even though your browser is up to date, its creators decided not to implement a given technology yet (for example, Opera Mini does not support the audio engine we use at all, even if its up-to-date on your device). In this case, we recommend you use the desktop version of AudioNodes (if you don't feel like switching browsers right now).
There are various reasons one cannot perform a browser update (such as being on a workplace computer). If you are allowed to install software, we suggest installing a supported browser (perhaps in addition to your already installed one), or use AudioNodes desktop.
If software installation is not an option, you might want to check out Google Chrome Portable, which supports the entire feature-set of AudioNodes Online.
The Modern WebAudio API setting can be enabled from Experimental Settings. On Mac (macbook, desktop), this can be enabled from the Develop menu. The Develop menu can be found at the top, but must be first enabled under Preferences -> Advanced -> "Show Develop menu in menu bar".
On iOS, the same can be found under Settings -> Safari -> Advanced -> Experimental Settings -> Modern WebAudio API.