我们正在开发一个项目,该项目允许我们使用一些低通滤波器和高通滤波器以 5k Hz 采样率从麦克风录制一些声音。
我们正在使用什么
我们正在使用音频引擎以此目的。
我们正在使用AVA音频转换器用于降低采样率。
我们正在使用AVAudioUnitEQ用于低通和高通滤波器。
Code
let bus = 0
let inputNode = engine.inputNode
let equalizer = AVAudioUnitEQ(numberOfBands: 2)
equalizer.bands[0].filterType = .lowPass
equalizer.bands[0].frequency = 3000
equalizer.bands[0].bypass = false
equalizer.bands[1].filterType = .highPass
equalizer.bands[1].frequency = 1000
equalizer.bands[1].bypass = false
engine.attach(equalizer) //Attach equalizer
// Connect nodes
engine.connect(inputNode, to: equalizer, format: inputNode.inputFormat(forBus: 0))
engine.connect(equalizer, to: engine.mainMixerNode, format: inputNode.inputFormat(forBus: 0))
engine.connect(engine.mainMixerNode, to: engine.outputNode, format: inputNode.inputFormat(forBus: 0))
let outputFormat = AVAudioFormat(commonFormat: .pcmFormatInt16,
sampleRate: 5000,
channels: 1,
interleaved: false)!
// Converter to downgrade sample rate
guard let converter: AVAudioConverter = AVAudioConverter(from: inputNode.inputFormat(forBus: 0), to: outputFormat) else {
print("Can't convert in to this format")
return
}
engine.mainMixerNode.installTap(onBus: bus, bufferSize: 2688, format: engine.mainMixerNode.outputFormat(forBus: 0)) { (buffer, time) in
var newBufferAvailable = true
let inputCallback: AVAudioConverterInputBlock = { inNumPackets, outStatus in
if newBufferAvailable {
outStatus.pointee = .haveData
newBufferAvailable = false
return buffer
} else {
outStatus.pointee = .noDataNow
return nil
}
}
let convertedBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat, frameCapacity: AVAudioFrameCount(outputFormat.sampleRate) * buffer.frameLength / AVAudioFrameCount(buffer.format.sampleRate))!
var error: NSError?
let status = converter.convert(to: convertedBuffer, error: &error, withInputFrom: inputCallback)
assert(status != .error)
if status == .haveData {
// Process with converted buffer
}
}
engine.prepare()
do {
try engine.start()
} catch {
print("Can't start the engine: \(error)")
}
Issue
低通和高通滤波器不起作用。
替代方法
为了检查代码是否正常工作,我们添加了混响效果而不是低通滤波器。
混响效果(使用AVAudioUnit混响) 使用相同的代码。
谁能帮我看看我们在应用低通滤波器时哪里做错了?