Compression/filtering across multiple devices - sample rates not accurate?

[tatulhum]

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I've tried recording with the demo (https://addpipe.com/simple-recorderjs-demo/) on several dozen different devices (smartphones, computers, tablets) and in a few different browsers. The recorded sample rate is 44.1 kHz or 48 kHz but upon inspecting the resulting wave files (by displaying spectrograms in Praat), the files are mostly all compressed (despite that the sample rates stated in the file info are 44.1 or 48 kHz), with everything above either 7.5-8 kHz (Android+some PCs) or 13 kHz (iOS) or 20-20.5 kHz (Macbooks) not recorded or filtered or something (blank/no noise) as if the sample rates were actually about 16 kHz, 26 kHz, and 40 kHz, respectively. Some of these devices I've tested making wave recordings in recorder apps and with these, they can record sample rates of 44.1 - 48 kHz without compression. Do other people have this issue with simple recorder.js? Does anyone know why this is happening or how to fix it? Having this compression/filtering or whatever it is defeats the benefits of an online .wav recorder.