声音的频谱显示

{
 Every line going into and out of the mixer has a number of "controls"
 associated with it. Some of those controls are "meters," which give
 you a real-time value of the sound level on the corresponding line.
 Not all lines have meter controls, and not all sound cards provide
 support for meters.
 Here's some code that will retrieve a handle to the meter attached to
 the WaveOut source of the speaker line, if there is one:
}
uses
 MMSystem;

procedure TForm1.Button1Click(Sender: TObject);
var
 MixerControl: TMixerControl;
 MixerControlDetails: TMixerControlDetails;
 MixerControlDetailsSigned: TMixerControlDetailsSigned;
 Mixer: THandle;
 MixerLine: TMixerLine;
 MixerLineControls: TMixerLineControls;
 PeakMeter: DWORD;
 Rslt: DWORD;
 SourceCount: Cardinal;
 WaveOut: DWORD;
 I: Integer;
 X: Integer;
 Y: Integer;
begin
 Rslt := mixerOpen(@Mixer, 0, 0, 0, 0);
 if Rslt <> 0 then
   raise Exception.CreateFmt('Can''t open mixer (%d)', [Rslt]);
 FillChar(MixerLine, SizeOf(MixerLine), 0);
 MixerLine.cbStruct := SizeOf(MixerLine);
 MixerLine.dwComponentType := MIXERLINE_COMPONENTTYPE_DST_SPEAKERS;
 Rslt := mixerGetLineInfo(Mixer, @MixerLine,
   MIXER_GETLINEINFOF_COMPONENTTYPE);
 if Rslt <> 0 then
   raise Exception.CreateFmt('Can''t find speaker line (%d)', [Rslt]);
 SourceCount := MixerLine.cConnections;
 WaveOut := $FFFFFFFF;
 for I := 0 to SourceCount - 1 do
 begin
   MixerLine.dwSource := I;
   Rslt := mixerGetLineInfo(Mixer, @MixerLine,
     MIXER_GETLINEINFOF_SOURCE);
   if Rslt <> 0 then
     raise Exception.CreateFmt('Can''t get source line (%d)', [Rslt]);
   if MixerLine.dwComponentType = MIXERLINE_COMPONENTTYPE_SRC_WAVEOUT then
   begin
     WaveOut := MixerLine.dwLineId;
     Break;
   end;
 end;
 if WaveOut = $FFFFFFFF then
   raise Exception.Create('Can''t find wave out device');
 FillChar(MixerLineControls, SizeOf(MixerLineControls), 0);
 with MixerLineControls do
 begin
   cbStruct := SizeOf(MixerLineControls);
   dwLineId := WaveOut;
   dwControlType := MIXERCONTROL_CONTROLTYPE_PEAKMETER;
   cControls := 1;
   cbmxctrl := SizeOf(TMixerControl);
   pamxctrl := @MixerControl;
 end;
 Rslt := mixerGetLineControls(Mixer, @MixerLineControls,
   MIXER_GETLINECONTROLSF_ONEBYTYPE);
 if Rslt <> 0 then
   raise Exception.CreateFmt('Can''t find peak meter control (%d)',
     [Rslt]);
 PeakMeter := MixerControl.dwControlID;
 // at this point, I have the meter control ID, so I can
 // repeatedly query its value and plot the resulting data
 // on a canvas
 X := 0;
 FillChar(MixerControlDetails, SizeOf(MixerControlDetails), 0);
 with MixerControlDetails do
 begin
   cbStruct := SizeOf(MixerControlDetails);
   dwControlId := PeakMeter;
   cChannels := 1;
   cbDetails := SizeOf(MixerControlDetailsSigned);
   paDetails := @MixerControlDetailsSigned;
 end;
 repeat
   Sleep(10);
   Rslt := mixerGetControlDetails(Mixer, @MixerControlDetails,
     MIXER_GETCONTROLDETAILSF_VALUE);
   if Rslt <> 0 then
     raise Exception.CreateFmt('Can''t get control details (%d)',
       [Rslt]);
   Application.ProcessMessages;
   Inc(X);
   Y := 300 - Round(300 * Abs(MixerControlDetailsSigned.lValue) / 32768);
   with Canvas do
   begin
     MoveTo(X, 0);
     Pen.Color := clBtnFace;
     LineTo(X, 300);
     Pen.Color := clWindowText;
     LineTo(X, Y);
   end;
 until X > 500;
 // don't forget to close the mixer handle when you're done
 Rslt := mixerClose(Mixer);
 if Rslt <> 0 then
   raise Exception.CreateFmt('Can''t close mixer (%d)', [Rslt]);
end;