Считать сигнал с микрофона

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Обратите внимание на MMSystem (подчеркнуто) в uses.

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, ComCtrls, MMSystem;

type
  TData8 = array [0..127] of byte;
  PData8 = ^TData8;
  TData16 = array [0..127] of smallint;
  PData16 = ^TData16;
  TPointArr = array [0..127] of TPoint;
  PPointArr = ^TPointArr;
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    PaintBox1: TPaintBox;
    TrackBar1: TTrackBar;
    CheckBox1: TCheckBox;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    procedure OnWaveIn(var Msg: TMessage); message MM_WIM_DATA;
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

var
  WaveIn: hWaveIn;
  hBuf: THandle;
  BufHead: TWaveHdr;
  bufsize: integer;
  Bits16: boolean;
  p: PPointArr;
  stop: boolean = false;

procedure TForm1.Button1Click(Sender: TObject);
var
  header: TWaveFormatEx;
  BufLen: word;
  buf: pointer;
begin
  BufSize := TrackBar1.Position * 500 + 100;
  Bits16 := CheckBox1.Checked;
  with header do begin
    wFormatTag := WAVE_FORMAT_PCM;
    nChannels := 1;
    nSamplesPerSec := 22050;
    wBitsPerSample := integer(Bits16) * 8 + 8;
    nBlockAlign := nChannels * (wBitsPerSample div 8);
    nAvgBytesPerSec := nSamplesPerSec * nBlockAlign;
    cbSize := 0;
  end;
  WaveInOpen(Addr(WaveIn), WAVE_MAPPER, addr(header),
    Form1.Handle, 0, CALLBACK_WINDOW);
  BufLen := header.nBlockAlign * BufSize;
  hBuf := GlobalAlloc(GMEM_MOVEABLE and GMEM_SHARE, BufLen);
  Buf := GlobalLock(hBuf);
  with BufHead do begin
    lpData := Buf;
    dwBufferLength := BufLen;
    dwFlags := WHDR_BEGINLOOP;
  end;
  WaveInPrepareHeader(WaveIn, Addr(BufHead), sizeof(BufHead));
  WaveInAddBuffer(WaveIn, addr(BufHead), sizeof(BufHead));
  GetMem(p, BufSize * sizeof(TPoint));
  stop := true;
  WaveInStart(WaveIn);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  if stop = false then Exit;
  stop := false;
  while not stop do Application.ProcessMessages;
  stop := false;
  WaveInReset(WaveIn);
  WaveInUnPrepareHeader(WaveIn, addr(BufHead), sizeof(BufHead));
  WaveInClose(WaveIn);
  GlobalUnlock(hBuf);
  GlobalFree(hBuf);
  FreeMem(p, BufSize * sizeof(TPoint));
end;

procedure TForm1.OnWaveIn;
var
  i: integer;
  data8: PData8;
  data16: PData16;
  h: integer;
  XScale, YScale: single;
begin
  h := PaintBox1.Height;
  XScale := PaintBox1.Width / BufSize;
  if Bits16 then begin
    data16 := PData16(PWaveHdr(Msg.lParam)^.lpData);
    YScale := h / (1 shl 16);
    for i := 0 to BufSize - 1 do
      p^[i] := Point(round(i * XScale),
        round(h / 2 - data16^[i] * YScale));
  end else begin
    Data8 := PData8(PWaveHdr(Msg.lParam)^.lpData);
    YScale := h / (1 shl 8);
    for i := 0 to BufSize - 1 do
      p^[i] := Point(round(i * XScale),
        round(h - data8^[i] * YScale));
  end;
  with PaintBox1.Canvas do begin
    Brush.Color := clWhite;
    FillRect(ClipRect);
    Polyline(Slice(p^, BufSize));
  end;
  if stop
    then WaveInAddBuffer(WaveIn, PWaveHdr(Msg.lParam),
      SizeOf(TWaveHdr))
    else stop := true;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Button2.Click;
end;