May 23, 2021
Pure Tone Generation
It has been a long time since I last wrote a posting for this blog.
I recently had an opportunity to create some Swift 5 code for generating and playing pure tones using AVFoundation. I put the code in a gist and thought I’d share it here.
The code uses a semaphore to block until the tone completes playing and plays the tone on a background thread. Even so, realize that the thread you are calling from will be blocked so you may need to wrap a call to the playPureTone(frequencyInHz, amplitude, durationInMillis, completion) function in a closure passed to a DispatchQue.
Enjoy.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| // | |
| // | |
| // Swift Pure Tone Generation | |
| // | |
| /* | |
| Copyright (c) 2021 Lee Barney | |
| Permission is hereby granted, free of charge, to any person obtaining a | |
| copy of this software and associated documentation files (the "Software"), | |
| to deal in the Software without restriction, including without limitation the | |
| rights to use, copy, modify, merge, publish, distribute, sublicense, | |
| and/or sell copies of the Software, and to permit persons to whom the Software | |
| is furnished to do so, subject to the following conditions: | |
| The above copyright notice and this permission notice shall be | |
| included in all copies or substantial portions of the Software. | |
| THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, | |
| INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A | |
| PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT | |
| HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF | |
| CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE | |
| OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | |
| */ | |
| import Foundation | |
| import AVFoundation | |
| func playPureTone(frequencyInHz: Int, amplitude: Float, durationInMillis: Int, completion: @escaping ()->Void) { | |
| //Use a semaphore to block until the tone completes playing | |
| let semaphore = DispatchSemaphore(value: 1) | |
| //Run async in the background so as not to block the current thread | |
| DispatchQueue.global().async { | |
| //Build the player and its engine | |
| let audioPlayer = AVAudioPlayerNode() | |
| let audioEngine = AVAudioEngine() | |
| semaphore.wait()//Claim the semphore for blocking | |
| audioEngine.attach(audioPlayer) | |
| let mixer = audioEngine.mainMixerNode | |
| let sampleRateHz = Float(mixer.outputFormat(forBus: 0).sampleRate) | |
| guard let format = AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: Double(sampleRateHz), channels: AVAudioChannelCount(1), interleaved: false) else { | |
| return | |
| } | |
| // Connect the audio engine to the audio player | |
| audioEngine.connect(audioPlayer, to: mixer, format: format) | |
| let numberOfSamples = AVAudioFrameCount((Float(durationInMillis) / 1000 * sampleRateHz)) | |
| //create the appropriatly sized buffer | |
| guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: numberOfSamples) else { | |
| return | |
| } | |
| buffer.frameLength = numberOfSamples | |
| //get a pointer to the buffer of floats | |
| let channels = UnsafeBufferPointer(start: buffer.floatChannelData, count: Int(format.channelCount)) | |
| let floats = UnsafeMutableBufferPointer<Float>(start: channels[0], count: Int(numberOfSamples)) | |
| //calculate the angular frequency | |
| let angularFrequency = Float(frequencyInHz * 2) * .pi | |
| // Generate and store the sequential samples representing the sine wave of the tone | |
| for i in 0 ..< Int(numberOfSamples) { | |
| let waveComponent = sinf(Float(i) * angularFrequency / sampleRateHz) | |
| floats[i] = waveComponent * amplitude | |
| } | |
| do { | |
| try audioEngine.start() | |
| } | |
| catch{ | |
| print("Error: Engine start failure") | |
| return | |
| } | |
| // Play the pure tone represented by the buffer | |
| audioPlayer.play() | |
| audioPlayer.scheduleBuffer(buffer, at: nil, options: .interrupts){ | |
| DispatchQueue.main.async { | |
| completionBlock() | |
| semaphore.signal()//Release one claim of the semiphore | |
| } | |
| } | |
| semaphore.wait()//Wait for the semiphore so the function doesn't end before the playing of the tone completes | |
| semaphore.signal()//Release the other claim of the semiphore | |
| } | |
| } |
Teton Technical 