uses
 MMSystem;
// Set the volume for the microphone
function SetMicrophoneVolume(bValue: Word): Boolean;
var  {0..65535}
 hMix: HMIXER;
 mxlc: MIXERLINECONTROLS;
 mxcd: TMIXERCONTROLDETAILS;
 vol: TMIXERCONTROLDETAILS_UNSIGNED;
 mxc: MIXERCONTROL;
 mxl: TMixerLine;
 intRet: Integer;
 nMixerDevs: Integer;
begin
 // Check if Mixer is available
 nMixerDevs := mixerGetNumDevs();
 if (nMixerDevs < 1) then
 begin
  Exit;
 end;
 // open the mixer
 intRet := mixerOpen(@hMix, 0, 0, 0, 0);
 if intRet = MMSYSERR_NOERROR then
 begin
  mxl.dwComponentType := MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE;
  mxl.cbStruct := SizeOf(mxl);
  // get line info
  intRet := mixerGetLineInfo(hMix, @mxl, MIXER_GETLINEINFOF_COMPONENTTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  ZeroMemory(@mxlc, SizeOf(mxlc));
  mxlc.cbStruct := SizeOf(mxlc);
  mxlc.dwLineID := mxl.dwLineID;
  mxlc.dwControlType := MIXERCONTROL_CONTROLTYPE_VOLUME;
  mxlc.cControls := 1;
  mxlc.cbmxctrl := SizeOf(mxc);
  mxlc.pamxctrl := @mxc;
  intRet := mixerGetLineControls(hMix, @mxlc, MIXER_GETLINECONTROLSF_ONEBYTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  {
  // Microphone Name
  Label1.Caption := mxlc.pamxctrl.szName;
  // Min/Max Volume
  Label2.Caption := IntToStr(mxc.Bounds.dwMinimum) + '->' + IntToStr(mxc.Bounds.dwMaximum);
  }
  ZeroMemory(@mxcd, SizeOf(mxcd));
  mxcd.dwControlID := mxc.dwControlID;
  mxcd.cbStruct := SizeOf(mxcd);
  mxcd.cMultipleItems := 0;
  mxcd.cbDetails := SizeOf(Vol);
  mxcd.paDetails := @vol;
  mxcd.cChannels := 1;
  // vol.dwValue := mxlc.pamxctrl.Bounds.lMinimum; Set min. Volume / Minimum setzen
  // vol.dwValue := mxlc.pamxctrl.Bounds.lMaximum; Set max. Volume / Maximum setzen
  vol.dwValue := bValue;
  intRet := mixerSetControlDetails(hMix, @mxcd,
  MIXER_SETCONTROLDETAILSF_VALUE);
  if intRet <> MMSYSERR_NOERROR then
  ShowMessage('SetControlDetails Error');
  end
  else
  ShowMessage('GetLineInfo Error');
  end;
  intRet := mixerClose(hMix);
 end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
 SetMicrophoneVolume(30000);
end;
{********************************************************}

// Enable/disable "Mute Microphone Volume"
function SetMicrophoneVolumeMute(bMute: Boolean): Boolean;
var
 hMix: HMIXER;
 mxlc: MIXERLINECONTROLS;
 mxcd: TMIXERCONTROLDETAILS;
 vol: TMIXERCONTROLDETAILS_UNSIGNED;
 mxc: MIXERCONTROL;
 mxl: TMixerLine;
 intRet: Integer;
 nMixerDevs: Integer;
 mcdMute: MIXERCONTROLDETAILS_BOOLEAN;
begin
 // Check if Mixer is available
 // Uberprufen, ob ein Mixer vorhanden ist
 nMixerDevs := mixerGetNumDevs();
 if (nMixerDevs < 1) then
 begin
  Exit;
 end;
 // open the mixer
 intRet := mixerOpen(@hMix, 0, 0, 0, 0);
 if intRet = MMSYSERR_NOERROR then
 begin
  mxl.dwComponentType := MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE;
  mxl.cbStruct := SizeOf(mxl);
  // mixerline info
  intRet := mixerGetLineInfo(hMix, @mxl, MIXER_GETLINEINFOF_COMPONENTTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  ZeroMemory(@mxlc, SizeOf(mxlc));
  mxlc.cbStruct := SizeOf(mxlc);
  mxlc.dwLineID := mxl.dwLineID;
  mxlc.dwControlType := MIXERCONTROL_CONTROLTYPE_MUTE;
  mxlc.cControls := 1;
  mxlc.cbmxctrl := SizeOf(mxc);
  mxlc.pamxctrl := @mxc;
  // Get the mute control
  intRet := mixerGetLineControls(hMix, @mxlc, MIXER_GETLINECONTROLSF_ONEBYTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  ZeroMemory(@mxcd, SizeOf(mxcd));
  mxcd.cbStruct := SizeOf(TMIXERCONTROLDETAILS);
  mxcd.dwControlID := mxc.dwControlID;
  mxcd.cChannels := 1;
  mxcd.cbDetails := SizeOf(MIXERCONTROLDETAILS_BOOLEAN);
  mxcd.paDetails := @mcdMute;
  mcdMute.fValue := Ord(bMute);
  // set, unset mute
  intRet := mixerSetControlDetails(hMix, @mxcd,
  MIXER_SETCONTROLDETAILSF_VALUE);
  {
  mixerGetControlDetails(hMix, @mxcd,
  MIXER_GETCONTROLDETAILSF_VALUE);
  Result := Boolean(mcdMute.fValue);
  }
  Result := intRet = MMSYSERR_NOERROR;
  if intRet <> MMSYSERR_NOERROR then
  ShowMessage('SetControlDetails Error');
  end
  else
  ShowMessage('GetLineInfo Error');
  end;
  intRet := mixerClose(hMix);
 end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
 SetMicrophoneVolumeMute(False);
end;

{********************************************************}
// Enable/disable "Mute" for several mixer line sources.
uses
 MMSystem;
type
 TMixerLineSourceType = (lsDigital, lsLine, lsMicrophone, lsCompactDisk, lsTelephone,
  lsWaveOut, lsAuxiliary, lsAnalog, lsLast);
function SetMixerLineSourceMute(AMixerLineSourceType: TMixerLineSourceType; bMute: Boolean): Boolean;
var
 hMix: HMIXER;
 mxlc: MIXERLINECONTROLS;
 mxcd: TMIXERCONTROLDETAILS;
 vol: TMIXERCONTROLDETAILS_UNSIGNED;
 mxc: MIXERCONTROL;
 mxl: TMixerLine;
 intRet: Integer;
 nMixerDevs: Integer;
 mcdMute: MIXERCONTROLDETAILS_BOOLEAN;
begin
 Result := False;
 // Check if Mixer is available
 nMixerDevs := mixerGetNumDevs();
 if (nMixerDevs < 1) then
 begin
  Exit;
 end;
 // open the mixer
 intRet := mixerOpen(@hMix, 0, 0, 0, 0);
 if intRet = MMSYSERR_NOERROR then
 begin
  ZeroMemory(@mxl, SizeOf(mxl));
  case AMixerLineSourceType of
  lsDigital: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_DIGITAL;
  lsLine: mxl.dwComponentType := MIXERLINE_COMPONENTTYPE_SRC_LINE;
  lsMicrophone: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE;
  lsCompactDisk: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_COMPACTDISC;
  lsTelephone: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_TELEPHONE;
  lsWaveOut: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_WAVEOUT;
  lsAuxiliary: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_AUXILIARY;
  lsAnalog : mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_ANALOG;
  lsLast: mxl.dwComponentType :=MIXERLINE_COMPONENTTYPE_SRC_LAST;
  end;
  // mixerline info
  mxl.cbStruct := SizeOf(mxl);
  intRet := mixerGetLineInfo(hMix, @mxl, MIXER_GETLINEINFOF_COMPONENTTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  ZeroMemory(@mxlc, SizeOf(mxlc));
  mxlc.cbStruct := SizeOf(mxlc);
  mxlc.dwLineID := mxl.dwLineID;
  mxlc.dwControlType := MIXERCONTROL_CONTROLTYPE_MUTE;
  mxlc.cControls := 1;
  mxlc.cbmxctrl := SizeOf(mxc);
  mxlc.pamxctrl := @mxc;
  // Get the mute control
  intRet := mixerGetLineControls(hMix, @mxlc, MIXER_GETLINECONTROLSF_ONEBYTYPE);
  if intRet = MMSYSERR_NOERROR then
  begin
  ZeroMemory(@mxcd, SizeOf(mxcd));
  mxcd.cbStruct := SizeOf(TMIXERCONTROLDETAILS);
  mxcd.dwControlID := mxc.dwControlID;
  mxcd.cChannels := 1;
  mxcd.cbDetails := SizeOf(MIXERCONTROLDETAILS_BOOLEAN);
  mxcd.paDetails := @mcdMute;
  mcdMute.fValue := Ord(bMute);
  // set, unset mute
  intRet := mixerSetControlDetails(hMix, @mxcd, MIXER_SETCONTROLDETAILSF_VALUE);
  {
  mixerGetControlDetails(hMix, @mxcd, IXER_GETCONTROLDETAILSF_VALUE);
  Result := Boolean(mcdMute.fValue);
  }
  Result := intRet = MMSYSERR_NOERROR;
  if intRet <> MMSYSERR_NOERROR then
  ShowMessage('SetControlDetails Error');
  end
  else
  ShowMessage('GetLineInfo Error');
  end;
  intRet := mixerClose(hMix);
 end;
end;
// Example Call;
procedure TForm1.Button1Click(Sender: TObject);
begin
 SetMixerLineSourceMute(lsLine, True);
end;