/*****************************************************************************
*                                                                            *
*   EFFBIT.SPL   Copyright (C) 2000 DSP Development Corporation              *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Abraham Goldsmith                                           *
*                                                                            *
*   Synopsis:    Calculates the number of effective bits based on the        *
*                frequency of a sample                                       *                                                                            *
*                                                                            *
*   Revisions:   25 Aug 2000  AG   Creation                                  *
*                                                                            *
*****************************************************************************/

#if @HELP_EFFBIT

    EFFBIT

    Purpose: Calculate the number of effective bits possible at a given
             frequency for a quantizing device.

    Syntax:  EFFBIT(s, freq, fs)

                  s - sinusoidal input series

               freq - known frequency of the input signal

                 fs - full scale input amplitude of the device being tested,
                      defaults to abs(max(s) - min(s)).

    Returns: a constant

    Example:
             W1: DATA1.1.TEST
             W2: EFFBIT( w1, 300, 40)

             Calculates the number of bits that are effective for every
             sample of the input data.

    Remarks:
             This routine uses the LSINFIT spl to match a sine wave
             to the input data. The number of effective bits is
             then calculated as:

                -log2( rms (input data - fitted sin wave) * sqrt(12) / FS)

    See Also:
             LSINFIT

    References:
             IEEE Std 1057-1994

#endif


/* effective bits calculation */
effbit(s, freq, fs)
{
        local fit, coef, eb, rmserror;

        if (argc < 3)
        {
                if (argc < 2)
                {
                        if (argc < 1)
                        {
                                error("effbit - input series required");
                        }

                        freq = -1;
                }
                
                fs = abs(max(s) - min(s));
        }
        
        /*
         *  Call SINFIT3 to return an ideal sine wave for the given frequency,
         *  (or unknown frequency) the fit coefficients and the rms error
         *  between the original signal and the fitted one, only the rms error
         *  is actually used.
         */
         
        (fit, coef, rmserror) = sinfit3(s, freq, 1);

        /* the effective bit calculation */
        eb = -log2(rmserror * sqrt(12) / fs);
        
        return(eb);
}