Path: super!cfreeseFrom: cfreese@super.ORG (Craig F. Reese)Newsgroups: comp.dspSubject: SPARCStation audio conversion (ulaw <-> linear)Message-ID: <14899@super.ORG>Date: 29 Sep 89 23:23:49 GMTSender: news@super.ORGReply-To: cfreese@super.UUCP (Craig F. Reese)Distribution: naOrganization: Supercomputing Research Center, Bowie, Md.Lines: 120TWIMC,Below are two routines I wrote for converting between ulaw and linear. I use them with the SparcStation and they seem to work fine.I am pretty sure (99.9%) that they implement the standard as specifiedin the references. Note that the standard deals with converting between 12 bit linearand 8 bit ulaw.  These routines assume 16 bit linear.  Thus, somebit shifting may be necessary.craig------------------------------------------------------------------/** ** Signal conversion routines for use with the Sun4/60 audio chip **//* * This routine converts from linear to ulaw * 29 September 1989 * * Craig Reese: IDA/Supercomputing Research Center * Joe Campbell: Department of Defense * * References: * 1) CCITT Recommendation G.711  (very difficult to follow) * 2) "A New Digital Technique for Implementation of Any  *     Continuous PCM Companding Law," Villeret, Michel, *     et al. 1973 IEEE Int. Conf. on Communications, Vol 1, *     1973, pg. 11.12-11.17 * 3) MIL-STD-188-113,"Interoperability and Performance Standards *     for Analog-to_Digital Conversion Techniques," *     17 February 1987 * * Input: Signed 16 bit linear sample * Output: 8 bit ulaw sample */#define ZEROTRAP    /* turn on the trap as per the MIL-STD */#define BIAS 0x84   /* define the add-in bias for 16 bit samples */#define CLIP 32635unsigned charlinear2ulaw(sample)int sample;{    static int exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,                               4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};    int sign, exponent, mantissa;    unsigned char ulawbyte;    /** get the sample into sign-magnitude **/    sign = (sample >> 8) & 0x80;        /* set aside the sign */    if (sign != 0) sample = -sample;    /* get magnitude */    if (sample > CLIP) sample = CLIP;   /* clip the magnitude */    /** convert from 16 bit linear to ulaw **/    sample = sample + BIAS;    exponent = exp_lut[(sample>>7) & 0xFF];    mantissa = (sample >> (exponent+3)) & 0x0F;    ulawbyte = ~(sign | (exponent << 4) | mantissa);#ifdef ZEROTRAP    if (ulawbyte == 0 ) ulawbyte = 0x02;  /* optional CCITT trap */#endif    /** return the result **/    return(ulawbyte);    }/* * This routine converts from ulaw to 16 bit linear * 29 September 1989 * * Craig Reese: IDA/Supercomputing Research Center * * References: * 1) CCITT Recommendation G.711  (very difficult to follow) * 2) MIL-STD-188-113,"Interoperability and Performance Standards *     for Analog-to_Digital Conversion Techniques," *     17 February 1987 * * Input: 8 bit ulaw sample * Output: signed 16 bit linear sample */intulaw2linear(ulawbyte)unsigned char ulawbyte;{    static int exp_lut[8]={0,132,396,924,1980,4092,8316,16764};    int sign, exponent, mantissa, sample;    ulawbyte = ~ulawbyte;    sign = (ulawbyte & 0x80);    exponent = (ulawbyte >> 4) & 0x07;    mantissa = ulawbyte & 0x0F;    sample = exp_lut[exponent] + (mantissa << (exponent+3));    if (sign != 0) sample = -sample;    return(sample);    }-----------------Craig F. Reese                           Email: cfreese@super.orgInstitute for Defense Analyses/Supercomputing Research Center17100 Science Dr.Bowie, MD  20715-4300