If not, or if you've got the feedback, you now need to tweak your sound recording settings. How to know? Run 'Sound Recorder' (or the Mac equivalent) and check that the sound guage is bouncing up and down indicating that audio is coming in the line in. If you don't hear the feedback, it may still be working (just not echoing the input back to the output, which is exactly what we want). That's because everything that comes in is being played out the stereo and then coming back to us again. You may immediately hear some insane staticy feedback and echoing. Play some Spotify, make sure you can hear it on the stereo - not too loud tho because. Unplug the line in from the computer for a sec. On my stereo it automatically directs the current input to the tape out, hopefully yours is the same - if not you need to turn on recording on your stereo and possibly direct the correct input to it. Get a RCA-to-headphone-jack cable and run from there to the mic or line-in jack on your computer (line-in is preferable if you have both). It's typically labled TAPE OUT or something on mine it's labled CD-R/TAPE. Most stereos have an output designed to send the audio output to a tape deck for recording. Some of this may not match your setup, but hopefully some of it will be useful anyway. I'm going to assume you want to use WinAmp with the default MilkDrop visualization plugin that it comes with.

I'll assume you have a secondary monitor, TV or projector plugged into the computer.

So I'm not going to go in to the messing around with 'loopback audio drivers' and whatnot, instead I'm going to assume you have your Spotify computer running into a stereo (if not, you can google 'loopback audio driver' but you're on your own with that). This used to be very easy to do in software, but these days it's become very difficult for dumb piracy prevention reasons and most drivers won't loop back. The key is looping the output of Spotify back to the input of your program that's doing the visualizations. This is not a question, I just wanted to share how I got this working so that I can use Spotify to play music on my laptop, while the secondary monitor plays visuals based on the Spotify output.

HOWTO: Spotify 'party-mode' with trippy visuals fr.

Play winamp line in