With a thriving community of audiophiles gravitating around the "#music" tag and a post type designed especially for audio, Tumblr's not a bad place for a music lover. Going from passive to active participant in the discussion often involves sharing music -- and to be shared, music has to be uploaded somewhere. When creating audio posts, you can choose from several different options as a music source, each with its upsides and downsides.
One way to create an audio post is to upload the file directly to Tumblr. Select the "Upload" tab on the posting screen, click "Choose File," browse to the file's location on your hard drive and double-click it to start uploading it. The file must be in MP3 format and may be no larger than 10MB. As of January 2014, you can only upload a maximum of five audio files a day in this manner. This limit applies to your entire account, not just individual blogs -- it doesn't matter whether you upload five files to one blog or one file to five different blogs.
You can't upload files to Spotify yourself, but it does deserve a mention. If the music you want to share could be even remotely classified as "popular," Spotify likely has it. Type the song title in the text field on the Search tab of the posting screen to see matching results; click one of the results to select it. Alternatively, you can paste the URL to a Spotify track, album or playlist in the text field on the "External URL" tab.
SoundCloud and Bandcamp
If you're a musician and want to share your own songs, you can sign up for an account on SoundCloud or Bandcamp. Both of these audio distribution services integrate with Tumblr in a manner similar to Spotify. Sharing a SoundCloud or Bandcamp song on Tumblr is simply a matter of pasting the URL to it in the text field on the "External URL" tab of the posting screen. You don't need to have uploaded a song yourself to share it in this way. Any song on SoundCloud and Bandcamp can be posted on Tumblr.
Other Hosting Services
Any hosting service works for posting audio to Tumblr, provided it allows you to link directly to uploaded files. Just paste or type the link to the audio file you want to share in the text field on the "External URL" tab of the posting screen. Keep in mind, though, that if the link doesn't end in ".mp3" the process won't work; Tumblr also doesn't support links that start with "https://" or that require a username and password. You could host the audio files on your own website, use a specialized audio hosting service such as Kiwi6, or even use a cloud storage service that gives you direct links to shared files, such as Dropbox.