this is sound quality test into amr narrowband codec, which is used gsm and umts networks. amr narrowband uses 4.75 kBit/s bandwith and 8 kHz sampling rate in these cases.

credits: Music: , Royalty Free Music from Bensound
original, mp3 file
original, wav file if mp3 does not work.
transformed into amr narrowband (and back to wav file)
transformed into amr narrowband, amr narrowband file

original, mp3 file
transformed into amr narrowband low quality file
transformed low quality back to wav file