How can I generate continuous tones of varying frequencies?

Question

I want to generate and play a continuous sound with specific frequencies and amplitudes that change over time. I don't want to have a delay between sounds. How can I do this with Delphi or C++ Builder?

Answer 1

By using WaveAudio library it's possible to generate a continous cosinus wave.

I was gonna post some code but I can't figure out how to do it properly so I won't.

But all you need to do is use TLiveAudioPlayer and then override the OnData event.

And also set Async to true if there is no message pump.

Answer 2

This very simple example should get you started.

program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils, Windows, MMSystem;

type
  TWaveformSample = integer; // signed 32-bit; -2147483648..2147483647
  TWaveformSamples = packed array of TWaveformSample; // one channel

var
  Samples: TWaveformSamples;
  fmt: TWaveFormatEx;

procedure InitAudioSys;
begin
  with fmt do
  begin
    wFormatTag := WAVE_FORMAT_PCM;
    nChannels := 1;
    nSamplesPerSec := 44100;
    wBitsPerSample := 32;
    nAvgBytesPerSec := nChannels * nSamplesPerSec * wBitsPerSample div 8;
    nBlockAlign := nChannels * wBitsPerSample div 8;
    cbSize := 0;
  end;
end;
                                          // Hz                     // msec
procedure CreatePureSineTone(const AFreq: integer; const ADuration: integer;
  const AVolume: double { in [0, 1] });
var
  i: Integer;
  omega,
  dt, t: double;
  vol: double;
begin
  omega := 2*Pi*AFreq;
  dt := 1/fmt.nSamplesPerSec;
  t := 0;
  vol := MaxInt * AVolume;
  SetLength(Samples, Round((ADuration / 1000) * fmt.nSamplesPerSec));
  for i := 0 to high(Samples) do
  begin
    Samples[i] := round(vol*sin(omega*t));
    t := t + dt;
  end;
end;

procedure PlaySound;
var
  wo: integer;
  hdr: TWaveHdr;
begin

  if Length(samples) = 0 then
  begin
    Writeln('Error: No audio has been created yet.');
    Exit;
  end;

  if waveOutOpen(@wo, WAVE_MAPPER, @fmt, 0, 0, CALLBACK_NULL) = MMSYSERR_NOERROR then
    try

      ZeroMemory(@hdr, sizeof(hdr));
      with hdr do
      begin
        lpData := @samples[0];
        dwBufferLength := fmt.nChannels * Length(Samples) * sizeof(TWaveformSample);
        dwFlags := 0;
      end;

      waveOutPrepareHeader(wo, @hdr, sizeof(hdr));
      waveOutWrite(wo, @hdr, sizeof(hdr));
      sleep(500);

      while waveOutUnprepareHeader(wo, @hdr, sizeof(hdr)) = WAVERR_STILLPLAYING do
        sleep(100);

    finally
      waveOutClose(wo);
    end;


end;


begin

  try
    InitAudioSys;
    CreatePureSineTone(400, 1000, 0.7);
    PlaySound;
  except
    on E: Exception do
    begin
      Writeln(E.Classname, ': ', E.Message);
      Readln;
    end;
  end;

end.

Notice in particular the neat interface you get:

    InitAudioSys;
    CreatePureSineTone(400, 1000, 0.7);
    PlaySound;