[Tftb-help] instfreq result

[Luis Torres]

    Hello. I am new using tftb.
    
    t1=0:0.001:1;
     t2=1:0.001:2;
     x1 = sin(t1*50*2*pi);
     x2 = sin(t2*75*2*pi);
     x = [x1 x2];
     plot(x);
     figure;
    [instf,t]=instfreq(x');
    plot(t,instf)
    
    I get ever 0.5 at the top and 0.25 values at the bottom. The unique
    difference is like the duty cycle between 50Hz part and the 75Hz
    part of the signal.
    Shall I calculate the mean value?

    How to get Hz frequencies from normalized. 
    I understood   f= w' * (fs/2)   but I get 0,5 normalized frequency
    at the top part of the returned value. 
    0.50  ->   f = 0.5*1000 = 250Hz in a 50Hz signal.
    0.25  ->    f = 0.25*1000 = 125Hz in a 50Hz signal.
    
    If i interpolate to 5KHz i get again 0.5 so 1250Hz. It has no sense.
    
    I have tried with a real signal captured at 1kHz rate and i get
    similar values.
    This is my Zero Crossing Frequency.

    I have read this thread from the mailing list but it does not
    resolve my question:
    
https://lists.nongnu.org/archive/html/tftb-help/2010-05/msg00001.html
    
    Thank you in advance.