Help with phase shift in Digital filter in MATLAB

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I am using fdatool in MATLAB to design digital filter. The sampling rate is 6400 Hz. Cutoff freqq=uency is 100 Hz.THe following is the screenshot:

Now the filter info shows that filter has linear phase. The input to the filter is a simple sine wave of 50Hz frequency, shown as this:
The output of the filter is this:
The output looks like distorted, not only phase shifted. How to extract original signal from this output? How to compensate the phase shift so as to get almost exact signal as input?
 

The input to the filter is a simple sine wave of 50Hz frequency
Click to expand...
It isn't a "simple sine wave".The input generating the shown output is a single sine cycle, not a continuous sine wave. The output looks respectively "distorted".

The output looks like distorted, not only phase shifted.
Click to expand...
According to the nature of FIR filter, the output is delayed by 20 samples, not phase shifted. The only way to "compensate" the filter effect is to delay the original signal, too.
 

Thanks. Yes this is just one cycle, actually i am trying to do frame based processing of signal. I have delayed input by 20 samples like:

However the output is:

Please tell me can i recover the peak value of the input from the output signal?
 

The filter arithmetics uses a tapped delay line so its output grows slowly and reaches maximum at the delay equal to half a length. For 40 order it is 20 samples.
If you dont want distorted signal just take two sinewave periods and remove first from analysis at the output. And dont delay input signal at the filter input, it is sensless.
 

Mityan said:
If you dont want distorted signal just take two sinewave periods and remove first from analysis at the output.
Click to expand...
This is completely correct and i have verified it. Thanks. Now only thing remaining is the problem with the amplitude of the signal. Input signal has peak equal to 1 whereas output signal has peak of about 0.85. Can i generalize the difference i.e. 0.15 for every signal filtered through this filter?
 

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