场景:在做播放设备的时候需要控制音量的大小，下面几种方法将满足你的要求

方法一: 改变系统音量设置

        [DllImport("user32.dll")]
        static extern void keybd_event(byte bVk, byte bScan, UInt32 dwFlags, UInt32 dwExtraInfo);

        [DllImport("user32.dll")]
        static extern Byte MapVirtualKey(UInt32 uCode, UInt32 uMapType);
	
        private const byte VK_VOLUME_MUTE = 0xAD;
        private const byte VK_VOLUME_DOWN = 0xAE;
        private const byte VK_VOLUME_UP = 0xAF;
        private const UInt32 KEYEVENTF_EXTENDEDKEY = 0x0001;
        private const UInt32 KEYEVENTF_KEYUP = 0x0002;

        /// <summary>
        /// 改变系统音量大小，增加
        /// </summary>
        public void VolumeUp()
        {
            keybd_event(VK_VOLUME_UP, MapVirtualKey(VK_VOLUME_UP, 0), KEYEVENTF_EXTENDEDKEY, 0);
            keybd_event(VK_VOLUME_UP, MapVirtualKey(VK_VOLUME_UP, 0), KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
        }

        /// <summary>
        /// 改变系统音量大小，减小
        /// </summary>
        public void VolumeDown()
        {
            keybd_event(VK_VOLUME_DOWN, MapVirtualKey(VK_VOLUME_DOWN, 0), KEYEVENTF_EXTENDEDKEY, 0);
            keybd_event(VK_VOLUME_DOWN, MapVirtualKey(VK_VOLUME_DOWN, 0), KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
        }

        /// <summary>
        /// 改变系统音量大小，静音
        /// </summary>
        public void Mute()
        {
            keybd_event(VK_VOLUME_MUTE, MapVirtualKey(VK_VOLUME_MUTE, 0), KEYEVENTF_EXTENDEDKEY, 0);
            keybd_event(VK_VOLUME_MUTE, MapVirtualKey(VK_VOLUME_MUTE, 0), KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
        }

        [DllImport("Winmm.dll")]
        private static extern int waveOutSetVolume(int hwo, System.UInt32 pdwVolume);

        [DllImport("Winmm.dll")]
        private static extern uint waveOutGetVolume(int hwo, out    System.UInt32 pdwVolume);  
        #region 

        private int volumeMinScope = 0;
        private int volumeMaxScope = 100;
        private int volumeSize = 100;

        /// <summary>
        /// 音量控制，但不改变系统音量设置
        /// </summary>
        public int VolumeSize
        {
            get { return volumeSize; }
            set { volumeSize = value; }
        }

        public void SetCurrentVolume()
        {
            if (volumeSize < 0)
            {
                volumeSize = 0;
            }

            if (volumeSize > 100)
            {
                volumeSize = 100;
            }
            System.UInt32 Value = (System.UInt32)((double)0xffff * (double)volumeSize / (double)(volumeMaxScope - v           

                      olumeMinScope));//先把trackbar的value值映射到0x0000～0xFFFF范围


            //限制value的取值范围
            if (Value < 0)
            {
                Value = 0;
            }

            if (Value > 0xffff)
            {
                Value = 0xffff;
            }

            System.UInt32 left = (System.UInt32)Value;//左声道音量
            System.UInt32 right = (System.UInt32)Value;//右
            waveOutSetVolume(0, left << 16 | right); //"<<"左移，“|”逻辑或运算
        }

C# 二种方法控制系统音量/麦克风大小