source: OniSplit/Sound/SoundData.cs@ 1135

using System;
using System.Collections.Generic;
using System.Text;

namespace Oni.Sound
{
    internal class SoundData
    {
        public bool IsIMA4;
        public int SampleRate;
        public int ChannelCount;
        public byte[] Data;

        public static SoundData Read(InstanceDescriptor sndd, bool do_pc_demo_test)
        {
            if (sndd.Template.Tag != TemplateTag.SNDD)
                throw new ArgumentException("descriptor");

            var sound = new SoundData();

            int dataSize;
            int dataOffset;

            using (var reader = sndd.OpenRead())
            {
                if (sndd.IsMacFile)
                {
                    sound.ChannelCount = (reader.ReadInt32() >> 1) + 1;
                    sound.SampleRate = 22050;
                    reader.Skip(4);
                    sound.IsIMA4 = true;
                }
                else
                {
                    reader.Skip(6); // ADPCM format identifiers (change to support PCM?)
                    sound.ChannelCount = reader.ReadInt16();
                    sound.SampleRate = reader.ReadInt32();
                    reader.Skip(44);
                    sound.IsIMA4 = false;
                }

                dataSize = reader.ReadInt32();
                dataOffset = reader.ReadInt32();
            }

            using (var rawReader = sndd.GetRawReader(dataOffset))
                sound.Data = rawReader.ReadBytes(dataSize);

            if (sound.IsIMA4 && do_pc_demo_test) // check if the raw data actually looks like IMA4
            {
                int nIMABlocks = sound.Data.Length / 34;
                int remainder = sound.Data.Length - nIMABlocks * 34;
                if (remainder == 0 && (nIMABlocks % sound.ChannelCount) == 0)
                {
                    bool stepIndexAbove88 = false;
                    for (int ii = 0; ii < nIMABlocks; ii++)
                    {
                        Byte cc = sound.Data[ii * 34 + 1];
                        if ((cc & 0x7F) > 88)
                            stepIndexAbove88 = true;
                    }
                    if (stepIndexAbove88)
                        sound.IsIMA4 = false;
                }
                else
                    sound.IsIMA4 = false;
                if (!(sound.IsIMA4))
                    Console.WriteLine("PC-demo MS ADPCM detected; use -nodemo flag to treat as IMA4.");
            }

            return sound;
        }
    }
}