Add more comments about normalization loudness

Author: yilun-zhangs

code/include/IAMF_decoder.h

@@ -136,6 +136,8 @@ char *IAMF_decoder_get_codec_capability();
  *            adjusted to the setting target.
  * @param     [in] handle : iamf decoder handle.
  * @param     [in] loundness : target normalization loudness in LKFS.
+ *                             0 dose not do normalization,
+ *                             others(<0) target value of normalization.
  * @return    @ref IAErrCode.
  */
 int IAMF_decoder_set_normalization_loudness(IAMF_DecoderHandle handle,
@@ -225,7 +227,6 @@ typedef struct IAMF_extradata {
 
 /**
  * @brief     Set the start timestamp and time base to decoder.
- *            max frame size could be gotten.
  * @param     [in] handle : iamf decoder handle.
  * @param     [in] pts : the start timestamp.
  * @param     [in] time_base : the time base used for pts.

code/src/iamf_dec/IAMF_decoder.c

@@ -40,6 +40,7 @@
 #define INVALID_TIMESTAMP 0xFFFFFFFF
 #define OUTPUT_SAMPLERATE 48000
 #define SPEEX_RESAMPLER_QUALITY 4
+#define MAX_LIMITED_NORMALIZATION_LOUDNESS 0.0f
 
 #define IAMF_DECODER_CONFIG_MIX_PRESENTATION 0x1
 #define IAMF_DECODER_CONFIG_OUTPUT_LAYOUT 0x2
@@ -3676,7 +3677,7 @@ static int iamf_decoder_internal_decode(IAMF_DecoderHandle handle,
       swap((void **)&f->data, (void **)&out);
     }
 
-    if (ctx->normalization_loudness) {
+    if (ctx->normalization_loudness < MAX_LIMITED_NORMALIZATION_LOUDNESS) {
       iamf_loudness_process(
           f->data, real_frame_size, ctx->output_layout->channels,
           db2lin(ctx->normalization_loudness - ctx->loudness));
@@ -3919,6 +3920,8 @@ IAMF_DecoderHandle IAMF_decoder_open(void) {
     handle->ctx.threshold_db = LIMITER_MaximumTruePeak;
     handle->ctx.loudness = 1.0f;
     handle->ctx.sampling_rate = OUTPUT_SAMPLERATE;
+    handle->ctx.normalization_loudness =
+        MAX_LIMITED_NORMALIZATION_LOUDNESS;
     handle->ctx.status = IAMF_DECODER_STATUS_INIT;
     handle->ctx.mix_presentation_id = INVALID_ID;
     handle->limiter = audio_effect_peak_limiter_create();

code/test/tools/iamfdec/src/test_iamfdec.c

@@ -101,7 +101,7 @@ static void print_usage(char *argv[]) {
   fprintf(stderr, "          12 : Sound system mono (0+1+0)\n");
   fprintf(stderr, "           b : Binaural.\n");
   fprintf(stderr, "-p [dB]      : Peak threshold in dB.\n");
-  fprintf(stderr, "-l [LKFS]    : Normalization loudness in LKFS.\n");
+  fprintf(stderr, "-l [LKFS]    : Normalization loudness(<0) in LKFS.\n");
   fprintf(stderr, "-d [bit]     : Bit depth of WAVE output.\n");
   fprintf(stderr, "-mp [id]     : Set mix presentation id.\n");
   fprintf(stderr,