如何在 C++ 中使用 fft 生成音频频谱？
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How to generate the audio spectrum using fft in C++?
提问by MRashid
I want to generate an audio spectrum (as seen in this video) of a mp3 audio file. Basically this problem requires calculating the fft of the audio signal. How do I program this in C/C++?
我想生成一个 mp3 音频文件的音频频谱（如本视频所示）。基本上这个问题需要计算音频信号的fft。我如何在 C/C++ 中编程？
I've looked at a couple of open source libraries such as FFTWand I really don't know how to use these for my problem. Any help would be greatly appreciated. Thanks in advance!
我查看了几个开源库，例如FFTW，但我真的不知道如何将它们用于解决我的问题。任何帮助将不胜感激。提前致谢！
回答by Paul R
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:
已经有很多关于 SO 的类似/相关问题非常值得一读，因为答案包含很多有用的信息和建议，但本质上你需要这样做：
- 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
- 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）
- 应用合适的窗口函数（例如Hann aka Hanning window）
- 应用 FFT（注意：如果使用典型的复数到复数 FFT，则将输入数组的虚部设置为零）
- 计算前 N/2 个 FFT 输出箱的幅度 (
sqrt(re*re + im*im)) - 可选择将幅度转换为 dB（对数）标度 (
20 * log10(magnitude)) - 绘制 N/2（对数）幅度值
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 KissFFTinstead.
请注意，虽然 FFTW 是一种非常好且速度非常快的 FFT，但它对于初学者来说可能有点不知所措 - 如果您想将其作为商业产品的一部分，它也非常昂贵 - 我建议从KissFFT开始。
