fix: Gain adjustment during second quantization phase can exceed minimum gain
diff --git a/src/spec.c b/src/spec.c
index 7b13578..f857f47 100644
--- a/src/spec.c
+++ b/src/spec.c
@@ -44,11 +44,12 @@
* nbits_off Offset on the available bits, temporarily smoothed
* g_off Gain index offset
* reset_off Return True when the nbits_off must be reset
+ * g_min Return lower bound of quantized gain value
* return The quantized gain value
*/
LC3_HOT static int estimate_gain(
enum lc3_dt dt, enum lc3_srate sr, const float *x,
- int nbits_budget, float nbits_off, int g_off, bool *reset_off)
+ int nbits_budget, float nbits_off, int g_off, bool *reset_off, int *g_min)
{
int ne = LC3_NE(dt, sr) >> 2;
int e[LC3_MAX_NE];
@@ -102,12 +103,12 @@
/* --- Limit gain index --- */
- int g_min = x2_max == 0 ? -g_off :
+ *g_min = x2_max == 0 ? -g_off :
ceilf(28 * log10f(sqrtf(x2_max) / (32768 - 0.375f)));
- *reset_off = g_int < g_min || x2_max == 0;
+ *reset_off = g_int < *g_min || x2_max == 0;
if (*reset_off)
- g_int = g_min;
+ g_int = *g_min;
return g_int;
}
@@ -118,10 +119,11 @@
* g_idx The estimated quantized gain index
* nbits Computed number of bits coding the spectrum
* nbits_budget Number of bits available for coding the spectrum
+ * g_idx_min Minimum gain index value
* return Gain adjust value (-1 to 2)
*/
-LC3_HOT static int adjust_gain(
- enum lc3_srate sr, int g_idx, int nbits, int nbits_budget)
+LC3_HOT static int adjust_gain(enum lc3_srate sr, int g_idx,
+ int nbits, int nbits_budget, int g_idx_min)
{
/* --- Compute delta threshold --- */
@@ -149,7 +151,7 @@
/* --- Adjust gain --- */
if (nbits < nbits_budget - (delta + 2))
- return -(g_idx > 0);
+ return -(g_idx > g_idx_min);
if (nbits > nbits_budget)
return (g_idx < 255) + (g_idx < 254 && nbits >= nbits_budget + delta);
@@ -789,8 +791,8 @@
int g_off = resolve_gain_offset(sr, nbytes);
- int g_int = estimate_gain(dt, sr,
- x, nbits_budget, nbits_off, g_off, &reset_off);
+ int g_min, g_int = estimate_gain(dt, sr,
+ x, nbits_budget, nbits_off, g_off, &reset_off, &g_min);
/* --- Quantization --- */
@@ -803,7 +805,8 @@
/* --- Adjust gain and requantize --- */
- int g_adj = adjust_gain(sr, g_int + g_off, nbits, nbits_budget);
+ int g_adj = adjust_gain(sr, g_off + g_int,
+ nbits, nbits_budget, g_off + g_min);
if (g_adj)
quantize(dt, sr, g_adj, x, xq, &side->nq);
diff --git a/test/spec.py b/test/spec.py
index 898c9a1..22c5e3e 100644
--- a/test/spec.py
+++ b/test/spec.py
@@ -589,7 +589,7 @@
(g_int, reset_off) = \
analysis.estimate_gain(x, nbits_budget, nbits_off, g_off)
- (g_int_c, reset_off_c) = lc3.spec_estimate_gain(
+ (g_int_c, reset_off_c, _) = lc3.spec_estimate_gain(
dt, sr, x, nbits_budget, nbits_off, -g_off)
ok = ok and g_int_c == g_int
@@ -664,7 +664,7 @@
g_adj = analysis.adjust_gain(g_idx, nbits, nbits_budget)
- g_adj_c = lc3.spec_adjust_gain(sr, g_idx, nbits, nbits_budget)
+ g_adj_c = lc3.spec_adjust_gain(sr, g_idx, nbits, nbits_budget, 0)
ok = ok and g_adj_c == g_adj
@@ -752,7 +752,7 @@
ok = ok and nbits == C.NBITS_EST[dt][i]
g_adj = lc3.spec_adjust_gain(sr,
- C.GG_IND[dt][i], C.NBITS_EST[dt][i], C.NBITS_SPEC[dt][i])
+ C.GG_IND[dt][i], C.NBITS_EST[dt][i], C.NBITS_SPEC[dt][i], 0)
ok = ok and g_adj == C.GG_IND_ADJ[dt][i] - C.GG_IND[dt][i]
if C.GG_IND_ADJ[dt][i] != C.GG_IND[dt][i]:
diff --git a/test/spec_py.c b/test/spec_py.c
index 814f253..730f68f 100644
--- a/test/spec_py.c
+++ b/test/spec_py.c
@@ -30,7 +30,7 @@
float *x;
int nbits_budget;
float nbits_off;
- int g_off;
+ int g_off, g_min;
bool reset_off;
if (!PyArg_ParseTuple(args, "IIOifi", &dt, &sr,
@@ -45,23 +45,24 @@
CTYPES_CHECK("x", x_obj = to_1d_ptr(x_obj, NPY_FLOAT, ne, &x));
int g_int = estimate_gain(dt, sr,
- x, nbits_budget, nbits_off, g_off, &reset_off);
+ x, nbits_budget, nbits_off, g_off, &reset_off, &g_min);
- return Py_BuildValue("ii", g_int, reset_off);
+ return Py_BuildValue("iii", g_int, reset_off, g_min);
}
static PyObject *adjust_gain_py(PyObject *m, PyObject *args)
{
unsigned sr;
- int g_idx, nbits, nbits_budget;
+ int g_idx, nbits, nbits_budget, g_idx_min;
- if (!PyArg_ParseTuple(args, "Iiii", &sr, &g_idx, &nbits, &nbits_budget))
+ if (!PyArg_ParseTuple(args, "Iiiii", &sr, &g_idx,
+ &nbits, &nbits_budget, &g_idx_min))
return NULL;
CTYPES_CHECK("sr", (unsigned)sr < LC3_NUM_SRATE);
CTYPES_CHECK("g_idx", g_idx >= 0 && g_idx <= 255);
- g_idx = adjust_gain(sr, g_idx, nbits, nbits_budget);
+ g_idx = adjust_gain(sr, g_idx, nbits, nbits_budget, g_idx_min);
return Py_BuildValue("i", g_idx);
}
