wscompand.c

// wscompand.c
// waveshaping compander, mostly for speech
/*
This file is part of a program that implements a Software-Defined Radio.

Copyright (C) 2004, 2005, 2006 by Frank Brickle, AB2KT and Bob McGwier, N4HY

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

The authors can be reached by email at

ab2kt@arrl.net
or
rwmcgwier@comcast.net

or by paper mail at

The DTTS Microwave Society
6 Kathleen Place
Bridgewater, NJ 08807
*/

#include <wscompand.h>

PRIVATE INLINE REAL
WSCLookup(WSCompander wsc, REAL x)
{
    if(x > 0.0)
    {
        REAL d = x - (int)x, y, *tbl = wsc->tbl;
        int i = (int)(x * wsc->npts), end = wsc->nend;
        if(i < end) y = tbl[i] + d * (tbl[i + 1] - tbl[i]);
        else y = tbl[end];
        return (y / x);
    } else return (0.0);
}

void
WSCompand(WSCompander wsc)
{
    int i, n = CXBsize(wsc->buff);

    for (i = 0; i < n; i++)
    {
        COMPLEX val = CXBdata(wsc->buff, i);
        REAL mag = Cmag(val), scl = WSCLookup(wsc, mag);
        CXBdata(wsc->buff, i) = Cscl(val, 0.8f * scl);
    }
}

void
WSCReset(WSCompander wsc, REAL fac)
{
    int i;
    REAL *tbl = wsc->tbl;

    if(fac == 0.0)       // just linear
        for (i = 0; i < wsc->npts; i++) tbl[i] = i / (REAL)wsc->nend;

    else
    {               // exponential
        REAL del = fac / wsc->nend, scl = (REAL)(1.0 - exp(fac));
        for (i = 0; i < wsc->npts; i++) tbl[i] = (REAL)((1.0 - exp(i * del)) / scl);
    }
    wsc->fac = fac;
}

// fac < 0: compression
// fac > 0: expansion

WSCompander
newWSCompander(int npts, REAL fac, CXB buff)
{
    WSCompander wsc;

    wsc = (WSCompander)safealloc(1,
                                 sizeof(WSCompanderInfo),
                                 "WSCompander struct");
    wsc->npts = npts;
    wsc->nend = npts - 1;
    wsc->tbl = newvec_REAL(npts, "WSCompander table");
    wsc->buff = newCXB(CXBsize(buff), CXBbase(buff), "WSCompander buff");
    WSCReset(wsc, fac);
    return (wsc);
}

void
delWSCompander(WSCompander wsc)
{
    if(wsc)
    {
        delvec_REAL(wsc->tbl);
        delCXB(wsc->buff);
        safefree((char *)wsc);
    }
}