错误的IO操作顺序使用putStr和getLine(Wrong IO actions order using putStr and getLine)

 在已经有很多类似/相关的问题上，这些问题值得一读，因为答案中包含了大量有用的信息和建议，但实质上你需要这样做： 
 
 
 
 将音频数据转换为FFT所需的格式（例如int - > float，单独的L / R通道） 
 
 
 应用合适的窗口功能 （例如Hann aka Hanning窗口 ） 
 
 
 应用FFT（注意：如果使用典型的复数到复数的FFT，则将输入数组的虚部设置为零） 
 
 
 计算第一个N / 2 FFT输出格的大小（ sqrt(re*re + im*im) ） 
 
 
 可选将幅度转换为dB（log）标度（ 20 * log10(magnitude) ） 
 
 
 绘制N / 2（对数）幅度值 
 
 
 请注意，尽管FFTW是一种非常好且非常快的FFT，但对于初学者来说可能会有些压倒性的影响 - 如果您想将其作为商业产品的一部分包含在内，它也非常昂贵 - 我建议从KissFFT开始。 

There are quite a few similar/related questions on SO already which are well worth reading as the answers contain a lot of useful information and advice, but in essence you need to do this:
 
 
 
convert audio data to format required by FFT (e.g. int -> float, separate L/R channels)
 
 
apply suitable window function (e.g. Hann aka Hanning window)
 
 
apply FFT (NB: if using typical complex-to-complex FFT then set imaginary parts of input array to zero)
 
 
calculate magnitude of first N/2 FFT output bins (sqrt(re*re + im*im))
 
 
optionally convert magnitude to dB (log) scale (20 * log10(magnitude))
 
 
plot N/2 (log) magnitude values
 
 
Note that while FFTW is a very good and very fast FFT it may be a little overwhelming for a beginner - it's also very expensive if you want to include it as part of a commercial product - I recommend starting with KissFFT instead.