Originally Posted by Spotify Help Site
What quality does Spotify stream in?
We use the Ogg Vorbis format for streaming. There are three quality ratings that we use:

q3 (~96 kbps)
q5 (~160 kbps)
q9 (~320 kbps)

Note: not all tracks are currently available in high bitrate.

Desktop: Streams are q5 quality. Premium subscribers can enable higher bit rate streaming at q9 from the preferences menu.

Mobile: A higher quality q5 is offered, along with a �low bandwidth� option of q3. You can choose separate qualities ratings for streaming and synching in the More tab of your Spotify mobile app.
I do find it strange that the Defaults on both the Spotify Desktop and Mobile Clients are for the lower bit rates........even for Premium Account holders

It's up to the User to go into the Settings and change the Default

Enough said from me......people can read the links, do their own investigations and make up their own minds on Spotify's Credibility

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