我有一个导航应用程序，它使用AVSpeechUtterance 提供方向语音指令（例如“在 200 英尺内左转”）。我已经把音量设置为 1 像这样。 speechUtteranceInstance.volume = 1，但与来自 iPhone 的音乐或播客相比，音量仍然非常低，尤其是当声音通过蓝牙或有线连接（如通过蓝牙连接到汽车）时
有什么办法可以提高音量吗？ （我知道之前有人问过这个问题，但到目前为止还没有找到适合我的解决方案。）
【问题讨论】：
标签： ios swift avaudioplayer avaudiosession avspeechutterance
经过大量研究和尝试，我找到了一个很好的解决方法。
首先，我认为这是一个 iOS 错误。当以下所有条件都成立时，我发现语音指令本身也被闪避（或至少听起来被闪避）导致语音指令以与 DUCKED 音乐相同的音量播放（因此太软而听不清）。
.duckOtheraudioSessionCategory我找到的解决方法是将 SpeechUtterance 提供给 AVAudioEngine。这只能在 iOS13 或更高版本上完成，因为这会添加 .write method to AVSpeechSynthesizer
简而言之，我使用AVAudioEngine、AVAudioUnitEQ 和AVAudioPlayerNode，将AVAudioUnitEQ 的 globalGain 属性设置为大约 10 dB。这也有一些怪癖，但可以解决它们（参见代码 cmets）。
完整代码如下：
import UIKit
import AVFoundation
import MediaPlayer
class ViewController: UIViewController {
// MARK: AVAudio properties
var engine = AVAudioEngine()
var player = AVAudioPlayerNode()
var eqEffect = AVAudioUnitEQ()
var converter = AVAudioConverter(from: AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatInt16, sampleRate: 22050, channels: 1, interleaved: false)!, to: AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: 22050, channels: 1, interleaved: false)!)
let synthesizer = AVSpeechSynthesizer()
var bufferCounter: Int = 0
let audioSession = AVAudioSession.sharedInstance()
override func viewDidLoad() {
super.viewDidLoad()
let outputFormat = AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: 22050, channels: 1, interleaved: false)!
setupAudio(format: outputFormat, globalGain: 0)
}
func activateAudioSession() {
do {
try audioSession.setCategory(.playback, mode: .voicePrompt, options: [.mixWithOthers, .duckOthers])
try audioSession.setActive(true, options: .notifyOthersOnDeactivation)
} catch {
print("An error has occurred while setting the AVAudioSession.")
}
}
@IBAction func tappedPlayButton(_ sender: Any) {
eqEffect.globalGain = 0
play()
}
@IBAction func tappedPlayLoudButton(_ sender: Any) {
eqEffect.globalGain = 10
play()
}
func play() {
let path = Bundle.main.path(forResource: "voiceStart", ofType: "wav")!
let file = try! AVAudioFile(forReading: URL(fileURLWithPath: path))
self.player.scheduleFile(file, at: nil, completionHandler: nil)
let utterance = AVSpeechUtterance(string: "This is to test if iOS is able to boost the voice output above the 100% limit.")
synthesizer.write(utterance) { buffer in
guard let pcmBuffer = buffer as? AVAudioPCMBuffer, pcmBuffer.frameLength > 0 else {
print("could not create buffer or buffer empty")
return
}
// QUIRCK Need to convert the buffer to different format because AVAudioEngine does not support the format returned from AVSpeechSynthesizer
let convertedBuffer = AVAudioPCMBuffer(pcmFormat: AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: pcmBuffer.format.sampleRate, channels: pcmBuffer.format.channelCount, interleaved: false)!, frameCapacity: pcmBuffer.frameCapacity)!
do {
try self.converter!.convert(to: convertedBuffer, from: pcmBuffer)
self.bufferCounter += 1
self.player.scheduleBuffer(convertedBuffer, completionCallbackType: .dataPlayedBack, completionHandler: { (type) -> Void in
DispatchQueue.main.async {
self.bufferCounter -= 1
print(self.bufferCounter)
if self.bufferCounter == 0 {
self.player.stop()
self.engine.stop()
try! self.audioSession.setActive(false, options: [])
}
}
})
self.converter!.reset()
//self.player.prepare(withFrameCount: convertedBuffer.frameLength)
}
catch let error {
print(error.localizedDescription)
}
}
activateAudioSession()
if !self.engine.isRunning {
try! self.engine.start()
}
if !self.player.isPlaying {
self.player.play()
}
}
func setupAudio(format: AVAudioFormat, globalGain: Float) {
// QUIRCK: Connecting the equalizer to the engine somehow starts the shared audioSession, and if that audiosession is not configured with .mixWithOthers and if it's not deactivated afterwards, this will stop any background music that was already playing. So first configure the audio session, then setup the engine and then deactivate the session again.
try? self.audioSession.setCategory(.playback, options: .mixWithOthers)
eqEffect.globalGain = globalGain
engine.attach(player)
engine.attach(eqEffect)
engine.connect(player, to: eqEffect, format: format)
engine.connect(eqEffect, to: engine.mainMixerNode, format: format)
engine.prepare()
try? self.audioSession.setActive(false)
}
}
【讨论】：
文档提到.volume 的默认值为 1.0，这是最响亮的。实际响度基于用户音量设置。如果用户调高音量，我并没有真正遇到语音不够响亮的问题。
如果用户音量级别低于某个级别，也许您可以考虑显示视觉警告。似乎this answer 展示了如何通过 AVAudioSession 做到这一点。
AVAudioSession 值得探索，因为有些设置确实会影响语音输出...例如，您的应用是否会中断来自其他应用的音频。
【讨论】：
试试这个：
import Speech
try? AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
let utterance = AVSpeechUtterance(string: "Hello world")
utterance.voice = AVSpeechSynthesisVoice(language: "en-GB")
let synthesizer = AVSpeechSynthesizer()
synthesizer.speak(utterance)
【讨论】：