胸哥和祐正學長在 20：35 離開了實驗室 就剩下我一個人了~~
正在想HHT的缺點在哪裡???
上周上課我所報告的PAPER 內容談到HHT應用於心音的好處
感覺 HHT 似乎非常強大
在時域、頻域、能量上做轉換
其中 EMD 所做出來 IMF 更為強大 應用性更好
雖然 HHT 在時域和頻域上可以做廣泛的訊號分析
卻還沒辦法完全取代 傅立葉轉換 和 小波轉換 ??
其中傅立葉轉換有限制時域和頻域 但在種種限制下
卻還是有很多研究堅持使用傅立葉轉換
最近正在看 HHT 在 EMG 上應用
裡面有幾段話 也不太懂到底在講甚麼
似乎在說 HHT 在 EMG訊號的種種缺失和不適用性
類似 所得到的瞬時頻率的震盪周期 會超過HHT的光譜信號範圍 (不懂...
以下是原文
several authors argued that one should not just take any data to perform a
Hilbert transform, find the phase function, and define the instantaneous
frequency as the derivative of this phase function.
They pointed out, if one follows this path, one would obtain a finite number
of points where the frequency becomes very high and even assumes negative
values that bear no relationship to the real oscillation of the data. It is
to say that the instantaneous frequency derived from this method is typically
oscillatory and often extends beyond the spectral range of the signal.
The instantaneous frequency concept is only meaningful for monocomponent or
narrow band signals. To obtain meaningful and well-behaved instantaneous
frequencies, the signal to be analyzed must have no riding waves and be
locally symmetrical about its mean point as defined by the envelopes of local
maxima and local minima .
This limitation of the data for the straight-forward application of Hilbert
transform means that the method is of little practical value on analysis of
EMG signal whose frequency band ranges from 30 to 300 Hz.
不解 誰可以幫我解答這邊再講什麼?? ><"
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