The levinson_durbin algorithm in lpc.c has a couple of arrays that are not
used. I changed the code to use just a variable instead. Not a lot of
memory saved, but this routine is called every encode frame (20 or 40 ms).
To check that the algorithm works the same, I used c2enc with hts1a.raw and
checked that the output values were the same. Here's a snippet:
Old algorithm: 1.000000 -1.930401 1.770051 -1.443837 0.961698 -0.523273
0.465262 -0.275403 0.496277 -0.624951
New algorithm: 1.000000 -1.930401 1.770051 -1.443837 0.961698 -0.523273
0.465262 -0.275403 0.496277 -0.624951
Old algorithm: 1.000000 -1.255710 0.800782 -1.023655 0.902301 -0.582309
0.414592 -0.220164 0.191661 -0.027249
New algorithm: 1.000000 -1.255710 0.800782 -1.023655 0.902301 -0.582309
0.414592 -0.220164 0.191661 -0.027249
diff -ruN freetel-code/codec2-dev/src/lpc.c
freetel-code-new/codec2-dev/src/lpc.c
--- freetel-code/codec2-dev/src/lpc.c 2014-06-26 08:08:06.042562836 -0500
+++ freetel-code-new/codec2-dev/src/lpc.c 2014-06-26 08:15:22.090549952
-0500
@@ -156,28 +156,26 @@
int order /* order of the LPC analysis */
)
{
- float E[order+1];
- float k[order+1];
float a[order+1][order+1];
- float sum;
+ float sum, e, k;
int i,j; /* loop variables */
- E[0] = R[0]; /* Equation 38a, Makhoul */
+ e = R[0]; /* Equation 38a, Makhoul */
for(i=1; i<=order; i++) {
sum = 0.0;
for(j=1; j<=i-1; j++)
sum += a[i-1][j]*R[i-j];
- k[i] = -1.0*(R[i] + sum)/E[i-1]; /* Equation 38b, Makhoul */
- if (fabsf(k[i]) > 1.0)
- k[i] = 0.0;
+ k = -1.0*(R[i] + sum)/e; /* Equation 38b, Makhoul */
+ if (fabsf(k) > 1.0)
+ k = 0.0;
- a[i][i] = k[i];
+ a[i][i] = k;
for(j=1; j<=i-1; j++)
- a[i][j] = a[i-1][j] + k[i]*a[i-1][i-j]; /* Equation 38c, Makhoul */
+ a[i][j] = a[i-1][j] + k*a[i-1][i-j]; /* Equation 38c, Makhoul */
- E[i] = (1-k[i]*k[i])*E[i-1]; /* Equation 38d, Makhoul */
+ e *= (1-k*k); /* Equation 38d, Makhoul */
}
for(i=1; i<=order; i++)
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