Streaming sites encode music at lower quality for playback.
If you don’t provide enough headroom, your music may clip and sound compressed. Find out the limitations of the playback codec and provide a suitable file.
Soundcloud, for example, recommends 16bit 48khz wav files with around -0.5 to -1dbFS headroom to prevent artefacts such as clipping.
You can test this yourself by exporting a WAV as a low quality mp3 and you will see that you will get intersample peaks after the process (unless you are giving sufficient headroom before hand).
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