如何用AVAudioEngine实现带阻滤波器

import AVFoundation
import AudioToolbox

let engine = AVAudioEngine()
let player = AVAudioPlayerNode()

let eq = AVAudioUnitEQ(numberOfBands: 1)
eq.bands[0].filterType = .bandStop
eq.bands[0].frequency = 1000 // 设置阻止频率
eq.bands[0].bandwidth = 100 // 设置阻止带宽

engine.attach(player)
engine.attach(eq)
engine.connect(player, to: eq, format: nil)
engine.connect(eq, to: engine.mainMixerNode, format: nil)

engine.prepare()
try? engine.start()

let audioFile = try AVAudioFile(forReading: audioURL)
player.scheduleFile(audioFile, at: nil)
player.play()