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This article explores how to generate tone with a predefined frequency programmatically through Delphi. Most of this article  consists of source code example.

Introduction

To produce tone with frequency defined at runtime, we can use Windows's Beep() function. This function is simple but unfortunately may not suit for some cases. For example, beep generated sound cannot be stored in a file.

This problem have arouse at Delphindo mailing list. Therefore, I decide to write article about it. For this article, I am going to develop tone generator application. I created this tone generator when I was involved in a active noise cancellation project, i.e, active noise reduction system where sound wave is damped by using same sound wave but out of phase 180 degree. ok let's go to code.

Tone Generator Implementation

Following code are declarations of types we use in tone generator and some helper functions. It is not too hard, is it?

{======================================
Sound type definition
=======================================
(c) 2006 zamrony p juhara
=======================================}
unit uSoundTypes;

interface

type

  TVolumeLevel = 0..127;
  TSampleRate=(sr8KHz,sr11_025KHz,sr22_05KHz,sr44_1KHz);
  TSoundChannel=(chMono,chStereo);
  TBitsPerSample=(bps8Bit,bps16Bit,bps32Bit);

function GetSampleRate(SampleRate:TSampleRate):integer;
function GetEnumSampleRate(SampleRate:integer):TSampleRate;

function GetNumChannels(ch:TSoundChannel):word;
function GetSoundChannels(nChannel:word):TSoundChannel;

function GetBitsPerSample(bits:TBitsPerSample):word;
function GetEnumBitsPerSample(bits:word):TBitsPerSample;

implementation


const SampleRates:array[sr8KHz..sr44_1KHz] of integer=
       (8000,11025,22050,44100);

     Channels:array[chMono..chStereo] of word=
     (1,2);
     BitsPerSample:array[bps8Bit..bps32Bit] of word=
     (8,16,32);

function GetSampleRate(SampleRate:TSampleRate):integer;
begin
  result:=SampleRates[SampleRate];
end;

function GetEnumSampleRate(SampleRate:integer):TSampleRate;
begin
  result:=sr8KHz;
  case sampleRate of
    8000:result:=sr8KHz;
    11025:result:=sr11_025KHz;
    22050:result:=sr22_05KHz;
    44100:result:=sr44_1KHz;
  end;
end;

function GetNumChannels(ch:TSoundChannel):word;
begin
  result:=Channels[ch];
end;

function GetSoundChannels(nChannel:word):TSoundChannel;
begin
  result:=chMono;
  case nChannel of
    1:result:=chMono;
    2:result:=chStereo;
  end;
end;

function GetBitsPerSample(bits:TBitsPerSample):word;
begin
  result:=BitsPerSample[bits];
end;