The channelCount and channelCountMode attributes for a ChannelSplitterNode are fixed to the number of outputs and "explicit", respectively. They cannot be changed.
Docs: https://webaudio.github.io/web-audio-api/#the-channelsplitternode-interface https://webaudio.github.io/web-audio-api/#widl-AudioNode-channelCount https://webaudio.github.io/web-audio-api/#widl-AudioNode-channelCountMode