There used to be this handy addon in firefox that would let you download just the audio of a youtube video. It seems to be gone and other addons dont seem to work. What do you use to rip just the audio? What browser?
Just paste the url from youtube, soundcloud etc...
You will complain that it only produces 128 bit rate MP3s. However, I believe this is because this is the bit rate that youtube, soundcloud etc... are delivering the audio to the listener regardless of what bit rate it was uploaded at.