如何生成给定频率的音频正弦波或方波?
我希望这样做能够校准设备,那么这些波浪的准确度如何?
您可以使用NAudio并创建派生的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位浮点样本,则可以直接从sin函数中写入值,而不必进行缩放,因为它已经介于-1和1之间.
至于准确度,你的意思是恰当的频率,还是恰好正确的波形?没有真正的方波,甚至正弦波也可能在其他频率上有一些非常安静的伪像.如果频率的准确性很重要,那么您依赖于声卡中时钟的稳定性和准确性.话虽如此,我认为准确性对于大多数用途来说已经足够了.
下面是一些示例代码,它以8 kHz采样率和16位采样(即非浮点)产生1 kHz采样:
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)); }
这使您可以给出频率,持续时间和幅度,它是100%.NET CLR代码.没有外部DLL.它的工作原理是创建一个WAV格式MemoryStream
,就像在内存中创建一个文件,而不是将其存储到磁盘.然后,它扮演的是MemoryStream
有System.Media.SoundPlayer
.
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)
尝试创建正弦并保存到C#中的wave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); }