Prevent click when stopping sounds

[ericrosenbaum]

Expected behavior

It should be possible to stop a sound while it's playing without causing a click.

Actual behavior

We're getting click sounds in several situations when sounds are stopped. This includes stopping sounds using the stop button, using the "stop all sounds" block, stopping and restarting a sound by playing it in a loop, and while navigating the sound library by hovering over sounds.

Steps to reproduce

Click the sounds tab
Click "Add Sound"
Add the sound "C Bass"
Run the following stack:

Things to try

Fortunately, in all these clicky situations, the same stop() function is called, here. We should be able to add a gain node to each bufferSourceNode and schedule a very short ramp down before stopping it.

Operating system and browser

Mac OS 10.11.6 Chrome 58.0