如何利用傅立叶变换从WAV文件中提取半precise频率 [英] How to extract semi-precise frequencies from a WAV file using Fourier Transforms

问题描述

让我们说，我有一个WAV文件。在这个文件中，是precise间隔1秒一连串正弦波音。我想使用的FFTW库按顺序提取这些音调。这是特别难呢？我怎么会去吗？

Let us say that I have a WAV file. In this file, is a series of sine tones at precise 1 second intervals. I want to use the FFTW library to extract these tones in sequence. Is this particularly hard to do? How would I go about this?

此外，什么是写这种色调成WAV文件的最好方法？我想我只需要一个简单的音频库的输出。

Also, what is the best way to write tones of this kind into a WAV file? I assume I would only need a simple audio library for the output.

我选择的语言是C

推荐答案

要得到一个部分的功率谱您的文件：

To get the power spectrum of a section of your file:

• 收集N个样本，其中N是2的幂 - 如果你的采样率44.1千赫例如，你想品尝大约每一秒，然后去说，N = 32768样品

• collect N samples, where N is a power of 2 - if your sample rate is 44.1 kHz for example and you want to sample approx every second then go for say N = 32768 samples.

应用合适的窗函数的样品，例如寒凝

apply a suitable window function to the samples, e.g. Hanning

传递窗采样到 FFT 程序 - 最好你想要一个真正的到复杂，但FFT如果你有一个复杂到复杂FFT那么对于所有的虚拟输入部分传递0

pass the windowed samples to an FFT routine - ideally you want a real-to-complex FFT but if all you have a is complex-to-complex FFT then pass 0 for all the imaginary input parts

计算你的FFT输出箱（重*重+ IM * IM）

calculate the squared magnitude of your FFT output bins (re * re + im * im)

（可选）计算出每级10 * log10的平方出纸槽，以获得分贝一个幅值

(optional) calculate 10 * log10 of each magnitude squared output bin to get a magnitude value in dB

现在，你有你的功率谱，你只需要确定峰（S），这应该是pretty简单，如果你有一个合理的S / N比率。注意，频率分辨率与较大N.改善有关的44.1千赫采样率和N = 32768上面的例子中每个仓的频率分辨率为44100/32768 = 1.35赫兹

Now that you have your power spectrum you just need to identify the peak(s), which should be pretty straightforward if you have a reasonable S/N ratio. Note that frequency resolution improves with larger N. For the above example of 44.1 kHz sample rate and N = 32768 the frequency resolution of each bin is 44100 / 32768 = 1.35 Hz.

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