So I've spent a lot of time comparing the native Spotify client with streaming Apple Music via Bluetooth. It's really a toss up to my ears. In summary, Spotify seems to have tighter bass at times, but then again it sometimes sounds a bit harsh overall to me. Apple Music seems to have a bit muddier bass, but it's not noticeable if that's the only thing you're listening to.
Today, though, I had some unused PTO that I needed to burn. I realized halfway through the day that I had the internet connection all to myself so it was prime time to do some experimenting. I have a SNMP endpoint that will tell me transfer rates and total transfers, up and down. I went to my car and brought up a playlist on Spotify that I had never listened to before.
I reset the totals on my SNMP monitor to zero and then played the first 5 songs, waiting about 30s on each song, on that playlist. And then looked at the totals
17.1 MB, but I do have residual traffic on my network so I timed 4 minutes of traffic without downloading any songs
About 2.5 MB over ~4 minutes which is about the time it took to do this test...I did say that this was totally unscientific.
Altogether, the songs add up to 16:18 or 978 seconds
(17.1 - 2.5 = 14.6 MB) / 16.3 min = 0.895 MB/min...but let's round that up to 0.9 to make it even less scientific
I mentioned earlier that I have Apple Music and my CD library was encoded at 256kbit so I started checking my library. Billy Joel's "This is the time" runs 5:02, the file size on my computer is 9.9MB. Blue Man Group's "Piano Smasher" runs 3:01 and weighs in at 6.9MB. Dire Straits' "Brothers in Arms" runs 6:59 and takes up 14.3MB. So roughly 2MB per minute or so.
My conclusion...Spotify is running around 128 kbits
I used this site to corroborate the files sizes for different bitrates as well