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How to create stereo wave files with accurate frequencies Turn on/off line numbers in source code. Switch to Orginial background IDE or DSP color Comment or reply to this aritlce/tip for discussion. Bookmark this article to my favorite article(s). Print this article
30-Aug-02
Category
Multimedia
Language
Delphi 2.x
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Publisher:
DSP, Administrator
Reference URL:
DKB
			Author: Tomas Rutkauskas

How do I generate low frequency audio < 1000 Hz with one frequency to the left 
channel and a slightly different frequency to the right? For example , a tone of 
400 Hz is presented to the right ear and a tone of 410 Hz is presented 
simultaneously to the left ear ? I'm trying to write a small binaural beat test 
program. I understand the science but not how to generate the two tones in Windows.

Answer:

Assuming you want precise control over the waveforms, the best thing to do is to 
create a stereo .WAV file containing the desired data. Here's a function that will 
do that; you can adapt it to your needs (add MMSystem to your USES list):


1   procedure CreateSineWave(LeftFreq, RightFreq: Single; Duration: Cardinal; 
2   const FileName: string);
3   const
4     BitsPerSample = 16;
5     NumChannels = 2;
6     SampleRate = 44100;
7   var
8     ChunkSize: Integer;
9     DataSize: Integer;
10    Factor: Single;
11    Format: TWaveFormatEx;
12    FourCC: array[0..3] of Char;
13    I: Integer;
14    NumSamples: Integer;
15    L: SmallInt;
16    R: SmallInt;
17    WaveStream: TFileStream;
18  begin
19    WaveStream := TFileStream.Create(FileName, fmCreate);
20    try
21      FourCC := 'RIFF';
22      WaveStream.write(FourCC, SizeOf(FourCC));
23      NumSamples := (SampleRate * Duration) div 1000;
24      DataSize := (BitsPerSample shr 3) * NumChannels * NumSamples;
25      ChunkSize := DataSize + SizeOf(TWaveFormatEx) + 20;
26      WaveStream.write(ChunkSize, SizeOf(ChunkSize));
27      FourCC := 'WAVE';
28      WaveStream.write(FourCC, SizeOf(FourCC));
29      FourCC := 'fmt ';
30      WaveStream.write(FourCC, SizeOf(FourCC));
31      ChunkSize := SizeOf(TWaveFormatEx);
32      WaveStream.write(ChunkSize, SizeOf(ChunkSize));
33      with Format do
34      begin
35        wFormatTag := WAVE_FORMAT_PCM;
36        nChannels := NumChannels;
37        nSamplesPerSec := SampleRate;
38        wBitsPerSample := BitsPerSample;
39        nBlockAlign := nChannels * wBitsPerSample shr 3;
40        nAvgBytesPerSec := nSamplesPerSec * nBlockAlign;
41        cbSize := 0
42      end;
43      WaveStream.write(Format, SizeOf(Format));
44      FourCC := 'data';
45      WaveStream.write(FourCC, SizeOf(FourCC));
46      ChunkSize := DataSize;
47      WaveStream.write(ChunkSize, SizeOf(ChunkSize));
48      for I := 0 to 999 do
49      begin
50        Factor := Exp(-0.005 * (1000 - I));
51        L := Round(Factor * 32767 * Sin(2 * Pi * LeftFreq * I / SampleRate));
52        R := Round(Factor * 32767 * Sin(2 * Pi * RightFreq * I / SampleRate));
53        WaveStream.write(L, SizeOf(L));
54        WaveStream.write(R, SizeOf(R))
55      end;
56      for I := 1000 to NumSamples - 1001 do
57      begin
58        L := Round(32767 * Sin(2 * Pi * LeftFreq * I / SampleRate));
59        R := Round(32767 * Sin(2 * Pi * RightFreq * I / SampleRate));
60        WaveStream.write(L, SizeOf(L));
61        WaveStream.write(R, SizeOf(R))
62      end;
63      for I := NumSamples - 1000 to NumSamples - 1 do
64      begin
65        Factor := Exp(0.005 * (NumSamples - 1001 - I));
66        L := Round(Factor * 32767 * Sin(2 * Pi * LeftFreq * I / SampleRate));
67        R := Round(Factor * 32767 * Sin(2 * Pi * RightFreq * I / SampleRate));
68        WaveStream.write(L, SizeOf(L));
69        WaveStream.write(R, SizeOf(R))
70      end;
71      WaveStream.Position := 0;
72    finally
73      WaveStream.Free
74    end
75  end;




So, for example, to create a two-second sample having a 400 Hz left channel and a 
410 Hz right channel:


76  CreateSineWave(400.0, 410.0, 2000, 'foo.wav');



You can play the sound like this:


77  sndPlaySound('foo.wav', SND_SYNC);


			
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