客户端锁定输出音量-PulseAudio

When I change the volume inside a pulse-audio client like VLC , the output volume in the pavucontrol->Output Device->Built-in Audio analog Stereo gets adjusted accordingly.So when I increase the volume inside VLC , the effect gets boosted and increases dramatically which is too loud even in 50% volume and vice versa.

Furthermore Volume up and Volume down system shortcuts increase the VLC volume beside increasing the system's. Looks like they're kind of locked to each other.

I use PulseAudio 11.1 in ubuntu bionic.

我该如何解锁?