/*****************************************************************************
*                                                                            *
*   MODPM.SPL    Copyright (C) 2019 DSP Development Corporation              *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Phase modulation of an input series                         *
*                                                                            *
*   Revisions:   10 Jan 2019  RRR  Creation                                  *
*                                                                            *
*****************************************************************************/

#if @HELP_MODPM

    MODPM

    Purpose: Performs phase modulation of a series.

    Syntax:  MODPM(s, fc, pdev, p0)

              s - the input series

             fc - Optional, a real. The center frequency of the phase
                  modulated result. Defaults to rate(s) / 10.

           pdev - Optional, a real. The phase deviation. Defaults to 
                  pi / 2;

             p0 - Optional, a real. The initial phase. Defaults to 0.0.

    Returns: A series, the phase modulated output.

    Example:
             W1: gtriwave(1000,.001, 4)
             W2: modpm(w1)
             W3: demodpm(w2)

             The triangle series of W1 is phase modulated between
             0 and pi/2 radians in W2. W3 recovers the modulated
             series.

    Example:
             W1: gtriwave(1000,.001, 4)
             W2: modpm(w1, 200, pi/3, pi/20)
             W3: demodpm(w2, 200, pi/3, pi/20)

             Same as above except the series is phase modulated at a center
             frequency of 200 Hz between 0 and pi/3 radians with an initial
             phase of pi/20 radians.

    Remarks:
             The center frequency, fc, should be less than rate(s) / 2.

             See DEMODPM to demodulate a phase modulated series.

    See Also:
             Modam
             Modfm
             Demodam
             Demodfm
             Demodpm
             Gsweep
             Specgram

#endif


/* phase modulate a series */
ITERATE modpm(s, fc, pdev, p0)
{
        local pm;

        if (argc < 4)
        {
                if (argc < 3)
                {
                        if (argc < 2)
                        {
                                if (argc < 1) error("modpm - input series required");
                        
                                fc = rate(s) / 10;
                        }
                
                        pdev = pi / 2;
                }

                p0 = 0;
        }        

        pm = cos(2 * pi * fc * xvals(s) + s * pdev + p0);
        
        return(pm);
}