Waveform Quantization and Compression - Digital Signal Processing: Fundamentals and Applications - page 531

// See Section 11.2 , Chapter 11
/* Segment

12-bit PCM 4-bit quantization interval */

/* 0 s0000000ABCD s000ABCD */

/* 1 s0000001ABCD s001ABCD */

/* 2 s000001ABCDX s010ABCD */

/* 3 s00001ABCDXX s011ABCD */

/* 4 s0001ABCDXXX s100ABCD */

/* 5 s001ABCDXXXX s101ABCD */

/* 6 s01ABCDXXXXX s110ABCD */

/* 7 s1ABCDXXXXXX s111ABCD */

//
/* Segment Recovered 12-bit PCM */
/* 0 s0000000ABCD */
/* 1 s0000001ABCD */
/* 2 s000001ABCD1 */
/* 3 s00001ABCD10 */
/* 4 s0001ABCD100 */
/* 5 s001ABCD1000 */
/* 6 s01ABCDq0000 */
/* 7 s1ABCD100000 */
/* Note that audio input/output data are in 2's complement form */
/* For encoder, convert the 2's complement form to the sign-magnitude form before
quantization */
/* For decoder, convert the sign-magnitude form to the 2's complement output before DAC */
interrupt void c_int11()
{

int lc; /*left channel input */
int rc; /*right channel input */
int lcnew; /*left channel output */
int rcnew; /*right channel output */
int tmp,ulawcode, dec;
//Left channel and right channel inputs
AIC23_data.combo ¼ input_sample();

lc ¼ (int) (AIC23_data.channel[LEFT]);

(int) (AIC23_data.channel[RIGHT]);
// Insert DSP algorithm below
/* Encoder :*/
tmp

rc ¼

lc;
if (tmp <0 )
{ tmp ¼ -tmp; // Get magnitude bits to work with
}
tmp ¼ (tmp>>4); // Linear scale down to 12 bits to use the u-255 law table
if( (tmp&0x07f0) ¼¼ 0x0) // Segment 0
{ ulawcode ¼ (tmp&0x000f); }
if( (tmp&0x07f0) ¼¼ 0x0010) // Segment 1
{ ulawcode ¼ (tmp&0x00f);
ulawcode ¼ ulawcode j 0x10; }
if( (tmp&0x07E0) ¼¼ 0x0020) // Segment 2

¼