控制音量——增益节点createGain()
let gainNode = audioCtx.createGain()
gainNode.gain.value = 0.5 // min 0 --> 1 max
source.connect(gainNode)
let gainNode = audioCtx.createGain()
gainNode.gain.value = 0.5 // min 0 --> 1 max
source.connect(gainNode)