在 C# 中創建正弦波或方波

Question

如何生成給定頻率的音頻正弦波或方波？

我希望這樣做是為了校准設備，那么這些波的精確度如何？

Answer 1

您可以使用NAudio並創建一個派生的 WaveStream 來輸出正弦波或方波，您可以將其輸出到聲卡或寫入WAV文件。 如果您使用 32 位浮點樣本，您可以直接從 sin 函數中寫入值，而無需縮放，因為它已經在 -1 和 1 之間。

至於准確性，您是指准確的頻率，還是完全正確的波形？ 沒有真正的方波這樣的東西，即使是正弦波，在其他頻率下也可能會有一些非常安靜的偽影。 如果重要的是頻率的准確性，則您依賴於聲卡中時鍾的穩定性和准確性。 話雖如此，我認為准確度對於大多數用途來說已經足夠了。

下面是一些示例代碼，它以 8 kHz 采樣率和 16 位采樣（即非浮點）生成 1 kHz 采樣：

int sampleRate = 8000;
short[] buffer = new short[8000];
double amplitude = 0.25 * short.MaxValue;
double frequency = 1000;
for (int n = 0; n < buffer.Length; n++)
{
    buffer[n] = (short)(amplitude * Math.Sin((2 * Math.PI * n * frequency) / sampleRate));
}

Answer 2

這讓你可以給出頻率、持續時間和幅度，它是 100% .NET CLR 代碼。 沒有外部DLL。 它通過創建一個 WAV 格式的MemoryStream ，就像只在內存中創建一個文件，而不將它存儲到磁盤。 然后它使用System.Media.SoundPlayer播放MemoryStream 。

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Windows.Forms;

public static void PlayBeep(UInt16 frequency, int msDuration, UInt16 volume = 16383)
{
    var mStrm = new MemoryStream();
    BinaryWriter writer = new BinaryWriter(mStrm);

    const double TAU = 2 * Math.PI;
    int formatChunkSize = 16;
    int headerSize = 8;
    short formatType = 1;
    short tracks = 1;
    int samplesPerSecond = 44100;
    short bitsPerSample = 16;
    short frameSize = (short)(tracks * ((bitsPerSample + 7) / 8));
    int bytesPerSecond = samplesPerSecond * frameSize;
    int waveSize = 4;
    int samples = (int)((decimal)samplesPerSecond * msDuration / 1000);
    int dataChunkSize = samples * frameSize;
    int fileSize = waveSize + headerSize + formatChunkSize + headerSize + dataChunkSize;
    // var encoding = new System.Text.UTF8Encoding();
    writer.Write(0x46464952); // = encoding.GetBytes("RIFF")
    writer.Write(fileSize);
    writer.Write(0x45564157); // = encoding.GetBytes("WAVE")
    writer.Write(0x20746D66); // = encoding.GetBytes("fmt ")
    writer.Write(formatChunkSize);
    writer.Write(formatType);
    writer.Write(tracks);
    writer.Write(samplesPerSecond);
    writer.Write(bytesPerSecond);
    writer.Write(frameSize);
    writer.Write(bitsPerSample);
    writer.Write(0x61746164); // = encoding.GetBytes("data")
    writer.Write(dataChunkSize);
    {
        double theta = frequency * TAU / (double)samplesPerSecond;
        // 'volume' is UInt16 with range 0 thru Uint16.MaxValue ( = 65 535)
        // we need 'amp' to have the range of 0 thru Int16.MaxValue ( = 32 767)
        double amp = volume >> 2; // so we simply set amp = volume / 2
        for (int step = 0; step < samples; step++)
        {
            short s = (short)(amp * Math.Sin(theta * (double)step));
            writer.Write(s);
        }
    }

    mStrm.Seek(0, SeekOrigin.Begin);
    new System.Media.SoundPlayer(mStrm).Play();
    writer.Close();
    mStrm.Close();
} // public static void PlayBeep(UInt16 frequency, int msDuration, UInt16 volume = 16383)

Answer 3

嘗試在 C# 中創建正弦並保存到波形文件

private void TestSine()
{
    IntPtr format;
    byte[] data;
    GetSineWave(1000, 100, 44100, -1, out format, out data);
    WaveWriter ww = new WaveWriter(File.Create(@"d:\work\sine.wav"),
        AudioCompressionManager.FormatBytes(format));
    ww.WriteData(data);
    ww.Close();
}

private void GetSineWave(double freq, int durationMs, int sampleRate, short decibel, out IntPtr format, out byte[] data)
{
    short max = dB2Short(decibel);//short.MaxValue
    double fs = sampleRate; // sample freq
    int len = sampleRate * durationMs / 1000;
    short[] data16Bit = new short[len];
    for (int i = 0; i < len; i++)
    {
        double t = (double)i / fs; // current time
        data16Bit[i] = (short)(Math.Sin(2 * Math.PI * t * freq) * max);
    }
    IntPtr format1 = AudioCompressionManager.GetPcmFormat(1, 16, (int)fs);
    byte[] data1 = new byte[data16Bit.Length * 2];
    Buffer.BlockCopy(data16Bit, 0, data1, 0, data1.Length);
    format = format1;
    data = data1;
}

private static short dB2Short(double dB)
{
    double times = Math.Pow(10, dB / 10);
    return (short)(short.MaxValue * times);
}

Answer 4

使用Math.NET 數字

https://numerics.mathdotnet.com/Generate.html

正弦

生成給定長度的正弦波陣列。 這等效於將縮放三角正弦函數應用於幅度為 2π 的周期性鋸齒波。

s(x)=A⋅sin(2πνx+θ)

Generate.Sinusoidal(length,samplingRate,frequency,amplitude,mean,phase,delay)

例如

 Generate.Sinusoidal(15, 1000.0, 100.0, 10.0);

返回數組 { 0, 5.9, 9.5, 9.5, 5.9, 0, -5.9, ... }

還有

Generate.Square(...

這將

創建一個周期性方波...

不能談精度。