If it's from your hard drive I'm pretty sure only you can hear it

So dropbox then

Late ass response, but I used github

引用自 AdamMAG37pl：

If you can, do only you will hear it, or others?

Yes, you can
But it is specific

Goto your Garry's mod folder
"Steam/Steamapps/Common/Garry's Mod/garrysmod" and create a "sound" folder.
Make a folder and name it the album name or something your song is from and put them in, if they do not play, the file is not supported. From my expirence .oggs, .mp3, and mp4s are compatible, but .wmv, wm2, mmw, .mpeg don't work.

Once you are done with that, type in your url browser in your radio "Foldername/Songname.extension"
For example : If you are listening to Tupac through it, 2pacalapse for the sake of conversation, Your directory is this
steam/steamapps/common/Garry's mod/garrysmod/sound/2pacalapse/2pacalapse.mp3

So type in the url browser :
2pacalapse/2pacalapse.mp3

Ambitionz az a ridah would be
steam/steamapps/common/Garry's mod/garrysmod/sound/All eyez on me/Ambitionz az a ridah.ogg

You just type anything past the sound directory and just type the folder name.
My english is kinda bad, but I am sure you got it.