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极坐标图象
( A0 T3 f; Y$ e5 @4 V( l, u" w Matlab中包括一个重要的函数叫做polar,它用于在极坐标系中画图。这个函数的基本形式如下:
# Y1 c; G/ A0 a) X6 y* t0 i) t$ fpolar(theta,r)
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" [+ g' \# P! C. F+ h其是theta代表一个弧度角数组,r代表一个距离数组。它用来画以角度为自变量的函数的极坐标图是非常有用的。
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心形麦克风 & w1 \6 j2 }: p* Q' H" T& K; z
为舞台表演设计的麦克风大多都是定向麦克风,它能够增大来自演唱者的信号,抑制后面观众的噪声信号。一个心形麦克风的增益gain是关于角度θ的函数,关系式如下
& \7 S, t" X$ _/ y& Q1 MGain=2g(1+cosθ) (3.3)
$ y1 E) G. i" z, r( z/ G其中g是和特定的心形麦克风有关的常量。θ是声源和麦克风之间的夹角。假设一个麦克风的g是0.5,画出函数Gain的极坐标图。
2 `2 H) A8 N& ^! X2 j8 n& @: M答案:我们必须计算出与角度对应的函数值,然后画出相应的极坐标图。产生的结果如图3.7所示。注意这种麦克风叫做心形麦克风,所以得出来曲线的形状像颗心。
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file:///C:/Users/lx/AppData/Local/Temp/msohtmlclip1/01/clip_image003.gif
$ E+ i* P3 ^3 N$ O) r( U1 U代码如下: ' w: ]& ^$ {+ ^8 u' u% Q
- <div align="left"><font face="Times New Roman"><font color="#000000">% Scriptfile: microphone.m</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%Purpose:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Thisprogram plots the gain pattern of a cardioid</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% microphone.</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Recordof revisions:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% DateProgrammer Description of change</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% ============== =====================</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% </font></font><font face="Times New Roman"><font color="#000000">12/10/97</font></font><font face="Times New Roman"><font color="#000000">S. J. Chapman Original code</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Definevariables:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% g --Microphone gain constant</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% gain --Gain as a function of angle</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% theta-- Angle from microphone axis (radians)</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%Calculate gain versus angle</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">g = 0.5;</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">theta =0:pi/20:2*pi;</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">gain =2*g*(1+cos(theta));</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Plotgain</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">polar(theta,gain,'r-');</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">title('Gain versus angle \it\theta');</font></font></div>
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