I discovered the reason for the scratchiness -- I had a typo in my code that decodes the nibbles. I think I screwed it up when I was copying the code over from the original IMA documentation. Here's the original code:
Here's the fixed code:
Stupid typos!
Here's the fixed chime, sounding MUCH better and probably perfect. Below is the complete working code:
I still get some warning printouts telling me the step index is less than 0 (which forces me to clamp it up to 0), but I think that's OK -- it's probably normal and just means the encoding wanted to keep it at 0. Anyway, great success on a Tuesday morning!
Code:
int diff = 0;
if (s & 4)
diff += step;
if (s & 2)
diff += step >> 1;
if (s & 4)
diff += step >> 2;
diff += step >> 3;
if (s &
diff = -diff;
Code:
int diff = 0;
if (s & 4)
diff += step;
if (s & 2)
diff += step >> 1;
if (s & 1)
diff += step >> 2;
diff += step >> 3;
if (s &
diff = -diff;Here's the fixed chime, sounding MUCH better and probably perfect. Below is the complete working code:
Code:
#include
#include
static const int ima_index_table[] = {
-1, -1, -1, -1, 2, 4, 6, 8,
-1, -1, -1, -1, 2, 4, 6, 8
};
static const int ima_step_table[] = {
7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};
#define NUM_STEP_TABLE_ENTRIES (sizeof(ima_step_table)/sizeof(ima_step_table[0]))
static int predictor = 0;
static int step_index = 0;
static int step = 7;
void do_header(uint8_t h)
{
predictor = (h << ;
if (predictor & 0x8000)
{
predictor |= 0xFFFF0000;
}
}
void do_header2(uint8_t h)
{
predictor |= (h & 0x80);
step_index = h & 0x7F;
if (step_index >= NUM_STEP_TABLE_ENTRIES)
{
printf("Header out of bounds\n");
step_index = NUM_STEP_TABLE_ENTRIES - 1;
}
step = ima_step_table[step_index];
}
void do_sample(uint8_t s, FILE *w)
{
step_index += ima_index_table[(uint8_t)s];
if (step_index < 0)
{
printf("Sample out of bounds < 0\n");
step_index = 0;
}
if (step_index >= NUM_STEP_TABLE_ENTRIES)
{
printf("Sample out of bounds >= %d\n", NUM_STEP_TABLE_ENTRIES);
step_index = NUM_STEP_TABLE_ENTRIES - 1;
}
// Sign-extend the nibble
if (s & 0x08){ s |= 0xF0; }
//int diff = (s + 0.5) * step / 4;
int diff = 0;
if (s & 4)
diff += step;
if (s & 2)
diff += step >> 1;
if (s & 1)
diff += step >> 2;
diff += step >> 3;
if (s &
diff = -diff;
predictor = predictor + diff;
if (predictor < -32768) predictor = -32768;
if (predictor > 32767) predictor = 32767;
step = ima_step_table[step_index];
int16_t value = predictor;
// This is me cheating to convert it back to big-endian for AIFF.
// Probably don't need to do it the way I did it, but whatever...
uint16_t tmpVal = (uint16_t)value;
uint16_t tmpVal2 = ((tmpVal & 0xFF) << | (tmpVal >> ;
fwrite(&tmpVal2, 2, 1, w);
}
int main(int argc, char *argv[])
{
uint32_t headersFound = 0;
uint32_t nibblesFound = 0;
uint32_t upperHeadersFound = 0;
FILE *f = fopen("SoundFile2.bin", "rb");
FILE *w = fopen("SoundFile.out", "wb");
int counter = 0;
uint8_t s;
while (fread(&s, 1, 1, f) > 0)
{
if ((counter % 34) == 0)
{
do_header(s);
}
else if ((counter % 34) == 1)
{
do_header2(s);
}
else
{
uint8_t s1 = s >> 4; // Most significant nibble
uint8_t s2 = s & 0x0F; // Least significant nibble
do_sample(s2, w);
do_sample(s1, w);
}
counter++;
}
fclose(f);
fclose(w);
}