I'm halfway through doing almost exactly this; a waterfall spectrum display. The data comes from real-time FFT (similar to Jan P's project) and one line is passed every 5ms as JSON into the web browser. The web browser accumulates packets and uses the browser's requestAnimationFrame to get a guaranteed time to render the content before the screen draws. Use the timeline tab in Chrome devtools to see how long your JS invocations are taking, and make sure you're not trying to do too much work in between frames. The animation frame rate will be a fraction of your display refresh interval, often a max of 60FPS, otherwise 30, 15, etc. Both HTML5 Canvas and SVG are fast enough though, if you do it right.
There's a graphic trick to make a continuously sliding waterfall. Mine slides sideways, not downwards, so I made a DIV twice as wide as the frame, and draw every vertical data line twice, separated by the width of the viewport (so one copy is off-screen). slide the underlying window one pixel sideways for each line you draw, until you hit the limit when you jump it back to the start.
I'm not available for this as a consult, and it's not my main project at the moment. But you've seen my impedance nomograph, so you know a little of my capabilities: .
I hope the above helps you. Contract prices for good front-end programmers who are capable of doing this kind of stuff well are pretty crazy.
Clifford Heath.