Estimation of Instantaneous Amplitude I'm reading a paper on EMG analysis. The formulas are all clear to me, but the paper refers to the signal amplitude as "instantaneous" amplitude.

I know what instantaneous mean, but what does it mean in the context of signal processing?
Instantaneous amplitude is usually done in conjunction with analytic signals and the Hilbert transform. See this answer on this site.


  For signal $s(t)$, given its Hilbert Transform $\hat{s}(t)$ it is defined as a composition:
  
  $$s_A(t)=s(t)+j\hat{s}(t) $$
  
  The Analytic Signal that we obtain is complex valued, therefore we can express it in exponential notation:
  
  $$s_A(t)=A(t)e^{j\psi(t)}$$
  
  where:
  
  $A(t)$ is the instantaneous amplitude (envelope)
  
  $\psi(t)$ is the instantaneous phase.