Some custom IWaveProvider... does not work

Program.cs

    class MuLawConversionProvider : IWaveProvider
    {
        private SampleToWaveProvider16 _sourceBuffer;
        private WaveFormat _theformat;

        public MuLawConversionProvider(SampleToWaveProvider16 SrcBuffer, WaveFormat theformat)
        {
            _sourceBuffer = SrcBuffer;
            _theformat = theformat;
        }

        public WaveFormat WaveFormat => throw new NotImplementedException();

        public int Read(byte[] destinationBuffer, int offset, int readingCount)
        {
            // Source buffer has twice as many items as the output array.
            var sizeOfPcmBuffer = readingCount * 2;
            //Cannot convert _sourceBuffer to byte[]???:
            _sourceBuffer = BufferHelpers.Ensure(_sourceBuffer, sizeOfPcmBuffer);
            var sourceBytesRead = _sourceProvider.Read(_sourceBuffer, offset * 2, sizeOfPcmBuffer);
            var samplesRead = sourceBytesRead / 2;

            var outIndex = 0;
            for (var n = 0; n < sizeOfPcmBuffer; n += 2)
            {
                destinationBuffer[outIndex++] = MuLawEncoder.LinearToMuLawSample(BitConverter.ToInt16(_sourceBuffer, offset + n));
            }

            return samplesRead * 2;
        }
    }