Is your browser’s volume set right in the volume mixer (if on windows)?
Other than that, I doubt that anyone will notice.. Are you sure that Audacity has mastered it properly? If you play it back through (for example) media player/iTunes does it still peak at -5dB?
No one will notice though, seriously.. There is enough rubbish on soundcloud that just being a little bit quiet won’t make you stand out as being “amateur” – although it is unmastered – proper mastering is an art in itself and usually needs a better DAW than audacity for it to sound good – I master in a new Logic project when I have done a mix (after bouncing the mix out of Logic) and still consider my mastering to be sub-par.. 🙂
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