AVSpeechSynthesizer buffer conversion, write format bug?

Is the format description AVSpeechSynthesizer for the speech buffer is correct? When I attempt to convert it, I get back noise from two different conversion methods.

I am seeking to convert the speech buffer provided by the AVSpeechSynthesizer "func write(_ utterance: AVSpeechUtterance..." method. The goal is to convert the sample type, change the sample rate and change from mono to stereo buffer. I later manipulate the buffer data and pass it through AVAudioengine. For testing purposes, I have kept the sample rate to the original 22050.0

What have I tried? I have a method that I've been using for years named "resampleBuffer" that does this. When I apply it to the speech buffer, I get back noise. When I attempt to manually convert format and to stereo with "convertSpeechBufferToFloatStereo", I am getting back clipped output. I tested flipping the samples, addressing the Big Endian, Signed Integer but that didn't work.

The speech buffer description is inBuffer description: <AVAudioFormat 0x6000012862b0: 1 ch, 22050 Hz, 'lpcm' (0x0000000E) 32-bit big-endian signed integer>

import Cocoa
import AVFoundation

class SpeakerTest: NSObject, AVSpeechSynthesizerDelegate {
    let synth = AVSpeechSynthesizer()

    override init() {
        super.init()
    }

    func resampleBuffer( inSource: AVAudioPCMBuffer, newSampleRate: Double) -> AVAudioPCMBuffer?
    {
        // resample and convert mono to stereo

        var error          : NSError?
        let kChannelStereo = AVAudioChannelCount(2)
        let convertRate    = newSampleRate / inSource.format.sampleRate
        let outFrameCount  = AVAudioFrameCount(Double(inSource.frameLength) * convertRate)
        let outFormat      = AVAudioFormat(standardFormatWithSampleRate: newSampleRate, channels: kChannelStereo)!
        let avConverter    = AVAudioConverter(from: inSource.format, to: outFormat )
        let outBuffer      = AVAudioPCMBuffer(pcmFormat: outFormat, frameCapacity: outFrameCount)!
        let inputBlock     : AVAudioConverterInputBlock = { (inNumPackets, outStatus) -> AVAudioBuffer? in
            outStatus.pointee = AVAudioConverterInputStatus.haveData // very important, must have
            let audioBuffer : AVAudioBuffer = inSource
            return audioBuffer
        }
        avConverter?.sampleRateConverterAlgorithm = AVSampleRateConverterAlgorithm_Mastering
        avConverter?.sampleRateConverterQuality   = .max

        if let converter = avConverter
        {
            let status = converter.convert(to: outBuffer, error: &error, withInputFrom: inputBlock)
//            print("\(status): \(status.rawValue)")
            if ((status != .haveData) || (error != nil))
            {
                print("\(status): \(status.rawValue), error: \(String(describing: error))")
                return nil // conversion error
            }
        } else {
            return nil // converter not created
        }
//        print("success!")
        return outBuffer
    }


    func writeToFile(_ stringToSpeak: String, speaker: String)
    {
        var output    : AVAudioFile?
        let utterance = AVSpeechUtterance(string: stringToSpeak)
        let desktop   = "~/Desktop"
        let fileName  = "Utterance_Test.caf" // not in sandbox
        var tempPath  = desktop + "/" + fileName
        tempPath      = (tempPath as NSString).expandingTildeInPath

        let usingSampleRate = 22050.0  // 44100.0
        let outSettings = [
            AVFormatIDKey            : kAudioFormatLinearPCM, // kAudioFormatAppleLossless
            AVSampleRateKey          : usingSampleRate,
            AVNumberOfChannelsKey    : 2,
            AVEncoderAudioQualityKey : AVAudioQuality.max.rawValue
        ] as [String : Any]


        // temporarily ignore the speaker and use the default voice
        let curLangCode  = AVSpeechSynthesisVoice.currentLanguageCode()
        utterance.voice  = AVSpeechSynthesisVoice(language: curLangCode)
//        utterance.volume = 1.0
        print("Int32.max: \(Int32.max), Int32.min: \(Int32.min)")

        synth.write(utterance) { (buffer: AVAudioBuffer) in
            guard let pcmBuffer = buffer as? AVAudioPCMBuffer else {
                fatalError("unknown buffer type: \(buffer)")
            }
            if ( pcmBuffer.frameLength == 0 ) {
                // done
            } else {
                // append buffer to file
                var outBuffer : AVAudioPCMBuffer
                outBuffer = self.resampleBuffer( inSource: pcmBuffer, newSampleRate: usingSampleRate)! // doesnt work
//                outBuffer = self.convertSpeechBufferToFloatStereo( pcmBuffer ) // doesnt work
//                outBuffer = pcmBuffer // original format does work

                if ( output == nil ) {
                    //var bufferSettings = utterance.voice?.audioFileSettings
                    // Audio files cannot be non-interleaved.
                    var outSettings = outBuffer.format.settings
                    outSettings["AVLinearPCMIsNonInterleaved"] = false

                    let inFormat    = pcmBuffer.format
                    print("inBuffer description: \(inFormat.description)")
                    print("inBuffer settings: \(inFormat.settings)")
                    print("inBuffer format: \(inFormat.formatDescription)")
                    print("outBuffer settings: \(outSettings)\n")
                    print("outBuffer format: \(outBuffer.format.formatDescription)")

                    output = try! AVAudioFile( forWriting: URL(fileURLWithPath: tempPath),settings: outSettings)
                }
                try! output?.write(from: outBuffer)
                print("done")
            }
        }
    }
}


class ViewController: NSViewController {
    let speechDelivery = SpeakerTest()

    override func viewDidLoad() {
        super.viewDidLoad()
        let targetSpeaker   = "Allison"
        var sentenceToSpeak = ""
        for indx in 1...10
        {
            sentenceToSpeak += "This is sentence number \(indx). [[slnc 3000]] \n"
        }
        speechDelivery.writeToFile(sentenceToSpeak, speaker: targetSpeaker)
    }
}

Three test can be performed. The only one that works is to directly write the buffer to disk

Is this really "32-bit big-endian signed integer"?

Am I addressing this correctly or is this a bug?

I'm on macOS 11.4