I need to introduce a metric for ECG signals after de-nosing operation to see the difference before and after that operation and the de-noising results.

I have worked with the procedure de-noising with 'wden' using wavelet 'sym8' and in particular I have to make a plot of this metric (square root or variance) of these two functions to see the difference before and after the operation of de-noising and maybe also use the autocorrelation to see if I eliminated the noise. how?? help me please

>> whos
   Name Size Bytes Class Attributes

   ecg_60_20_f 80000 10000x1 double
>> lev = 5;
>> xd = wden (ecg_60_20_f, 'heursure', 's', 'one', lev, 'sym8');
>> Plot (ecg_60_20_f); hold on;
>> Plot (xd, 'r', 'linewidth', 2)
>> Legend ('Original signal', 'denoised signal')