在C＃中创build正弦波或方波
如何产生给定频率的audio正弦波或方波？
我希望这样做来校准设备，那么这些浪潮究竟有多精确呢？
您可以使用NAudio创build派生的WaveStream，输出正弦波或方波，您可以将其输出到声卡或写入WAV文件。 如果使用32位浮点数样本，则可以将值直接写出sin函数，而不必进行缩放，因为它已经在-1和1之间。
至于准确性，你的意思是恰到好处的频率，还是正确的波形？ 没有真正的方波这样的东西，甚至正弦波在其他频率可能会有一些非常安静的文物。 如果重要的是频率的准确性，那么您就依赖于声卡中时钟的稳定性和准确性。 话虽如此，我可以想象大多数用途的准确性是足够好的。
以下是一些以8 kHz采样率和16位采样（即不是浮点）形成1 kHz采样的示例代码：
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)); } 这可以让你给出频率，持续时间和幅度，它是100％的.NET CLR代码。 没有外部DLL的。 它的工作原理是创build一个WAV格式的MemoryStream ，就像在内存中创build一个文件一样，不需要将其存储到磁盘。 然后它与System.Media.SoundPlayer一起播放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)
尝试从创build正弦波并保存到C＃中的波形文件
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); }
