求翻译：由于心音信号在时域并不稀疏，我们将观测信号作频域处理。观测信号经快速傅里叶变换后所得信号的频域散列图如图3所示。是什么意思？

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When they heard from him in my heart because of sparse domain does not, we will be observing signal frequency domain processing. Observing signals after the Fast Fourier Transform signals derived from the frequency domain hash map as shown in figure 3.

Because the sound of the heart signal is not sparse in the time domain, we will observe the signal to make frequency range processing.The observation signal the obtained signal frequency range disperses row chart as shown in Figure after the fast Fournier transformation 3.

As heart sound signal in the time domain is not sparse, we will observe for frequency domain signal processing. After Fast Fourier transform, the observed signal received signal in frequency-domain hash map as shown in Figure 3.

As heart sound signal in the time domain is not sparse, we will observe for frequency domain signal processing. After Fast Fourier transform, the observed signal received signal in frequency-domain hash map as shown in Figure 3.