在进行机器人项目信号处理研究时，发现C#编写的示例代码较为罕见。这促使创建了一些自己的类，这里展示的代码就是用于演示的。
本文主要介绍了如何利用C#和Windows GDI实现声音信号的实时可视化。通过Fast Fourier Transform（快速傅里叶变换）和Windows GDI，可以将声音信号在时间和频率域的表示形式进行可视化。
在进行机器人项目信号处理研究时，发现C#编写的示例代码较为罕见。这促使创建了一些自己的类，这里展示的代码就是用于演示的。
本文的演示使用Ianier Munoz开发的Wave类来提供音频输入。Wave样本进一步使用AudioFrame类进行处理。
AudioFrame类是C#中一个用于处理音频样本的类，它包含画布、波形数据、快速傅里叶变换数据等成员。
AudioFrame类的主要功能是处理16位音频样本，并将其在时间和频率域的可视化渲染到PictureBox控件中。
AudioFrame类中的Process方法用于处理16位音频样本。如果_isTest为false，则从样本中分离出左右声道；如果为true，则生成人工样本用于测试。
public void Process(ref byte[] wave)
{
_waveLeft = new double[wave.Length / 4];
_waveRight = new double[wave.Length / 4];
if (!_isTest)
{
// 分离出左右声道
int h = 0;
for (int i = 0; i < wave.Length; i += 4)
{
_waveLeft[h] = (double)BitConverter.ToInt16(wave, i);
_waveRight[h] = (double)BitConverter.ToInt16(wave, i + 2);
h++;
}
}
else
{
// 生成人工样本用于测试
_signalGenerator = new SignalGenerator();
_signalGenerator.SetWaveform("Sine");
_signalGenerator.SetSamplingRate(44100);
_signalGenerator.SetSamples(16384);
_signalGenerator.SetFrequency(5000);
_signalGenerator.SetAmplitude(32768);
_waveLeft = _signalGenerator.GenerateSignal();
_waveRight = _signalGenerator.GenerateSignal();
}
// 生成频率域数据
_fftLeft = FourierTransform.FFTDb(ref _waveLeft);
_fftRight = FourierTransform.FFTDb(ref _waveRight);
}
RenderTimeDomain方法用于将时间域数据渲染到PictureBox控件中。首先设置绘图环境，然后确定左右声道的边界，接着绘制左右声道的波形。
public void RenderTimeDomain(ref PictureBox pictureBox)
{
// 设置绘图环境
_canvasTimeDomain = new Bitmap(pictureBox.Width, pictureBox.Height);
Graphics offScreenDC = Graphics.FromImage(_canvasTimeDomain);
SolidBrush brush = new System.Drawing.SolidBrush(Color.FromArgb(0, 0, 0));
Pen pen = new System.Drawing.Pen(Color.WhiteSmoke);
// 确定左右声道的边界
int width = _canvasTimeDomain.Width;
int center = _canvasTimeDomain.Height / 2;
int height = _canvasTimeDomain.Height;
offScreenDC.DrawLine(pen, 0, center, width, center);
// 绘制左声道
double yCenterLeft = (leftBottom - leftTop) / 2;
double yScaleLeft = 0.5 * (leftBottom - leftTop) / 32768;
int xPrevLeft = 0, yPrevLeft = 0;
for (int xAxis = leftLeft; xAxis < leftRight; xAxis++)
{
int yAxis = (int)(yCenterLeft + (_waveLeft[_waveLeft.Length / (leftRight - leftLeft) * xAxis] * yScaleLeft));
if (xAxis == 0)
{
xPrevLeft = 0;
yPrevLeft = yAxis;
}
else
{
pen.Color = Color.LimeGreen;
offScreenDC.DrawLine(pen, xPrevLeft, yPrevLeft, xAxis, yAxis);
xPrevLeft = xAxis;
yPrevLeft = yAxis;
}
}
// 绘制右声道
double yScaleRight = 0.5 * (rightBottom - rightTop) / 32768;
int xCenterRight = rightTop + ((rightBottom - rightTop) / 2);
int xPrevRight = 0, yPrevRight = 0;
for (int xAxis = rightLeft; xAxis < rightRight; xAxis++)
{
int yAxis = (int)(xCenterRight + (_waveRight[_waveRight.Length / (rightRight - rightLeft) * xAxis] * yScaleRight));
if (xAxis == 0)
{
xPrevRight = 0;
yPrevRight = yAxis;
}
else
{
pen.Color = Color.LimeGreen;
offScreenDC.DrawLine(pen, xPrevRight, yPrevRight, xAxis, yAxis);
xPrevRight = xAxis;
yPrevRight = yAxis;
}
}
// 清理
pictureBox.Image = _canvasTimeDomain;
offScreenDC.Dispose();
}
public void RenderFrequencyDomain(ref PictureBox pictureBox)
{
// 设置绘图环境
_canvasFrequencyDomain = new Bitmap(pictureBox.Width, pictureBox.Height);
Graphics offScreenDC = Graphics.FromImage(_canvasFrequencyDomain);
SolidBrush brush = new System.Drawing.SolidBrush(Color.FromArgb(0, 0, 0));
Pen pen = new System.Drawing.Pen(Color.WhiteSmoke);
// 确定左右声道的边界
int width = _canvasFrequencyDomain.Width;
int center = _canvasFrequencyDomain.Height / 2;
int height = _canvasFrequencyDomain.Height;
offScreenDC.DrawLine(pen, 0, center, width, center);
// 绘制左声道
for (int xAxis = leftLeft; xAxis < leftRight; xAxis++)
{
double amplitude = (int)_fftLeft[(int)(((double)(_fftLeft.Length) / (double)(width)) * xAxis)];
if (amplitude < 0)
amplitude = 0;
int yAxis = (int)(leftTop + ((leftBottom - leftTop) * amplitude) / 100);
pen.Color = Color.FromArgb(0, 0, (int)amplitude % 255);
offScreenDC.DrawLine(pen, xAxis, leftTop, xAxis, yAxis);
}
// 绘制右声道
for (int xAxis = rightLeft; xAxis < rightRight; xAxis++)
{
double amplitude = (int)_fftRight[(int)(((double)(_fftRight.Length) / (double)(width)) * xAxis)];
if (amplitude < 0)
amplitude = 0;
int yAxis = (int)(rightBottom - ((rightBottom - rightTop) * amplitude) / 100);
pen.Color = Color.FromArgb(0, 0, (int)amplitude % 255);
offScreenDC.DrawLine(pen, xAxis, rightBottom, xAxis, yAxis);
}
// 清理
pictureBox.Image = _canvasFrequencyDomain;
offScreenDC.Dispose();
}