mp3 samples are signed

shared-module/audiomp3/MP3Decoder.c

@@ -385,7 +385,7 @@ void common_hal_audiomp3_mp3file_set_file(audiomp3_mp3file_obj_t *self, mp_obj_t
     self->base.channel_count = fi.nChans;
     self->base.single_buffer = false;
     self->base.bits_per_sample = 16;
-    self->base.samples_signed = false;
+    self->base.samples_signed = true;
     self->base.max_buffer_length = fi.outputSamps * sizeof(int16_t);
     self->len = 2 * self->base.max_buffer_length;
     self->samples_decoded = 0;

tests/circuitpython/issue9705.py

@@ -1,25 +1,19 @@
 import audiomp3, audiocore
-import ulab.numpy as np
 
 TEST_FILE = (
     __file__.rsplit("/", 1)[0]
     + "/../circuitpython-manual/audiocore/jeplayer-splash-44100-stereo.mp3"
 )
 
 
-def normalized_rms_ulab(values):
-    values = np.frombuffer(values, dtype=np.int16)
-    # this function works with ndarrays only
-    minbuf = np.mean(values)
-    values = values - minbuf
-    samples_sum = np.sum(values * values)
-    return (samples_sum / len(values)) ** 0.5
+def loudness(values):
+    return sum(abs(a) for a in values)
 
 
 def print_frame_loudness(decoder, n):
     for i in range(n):
         result, buf = audiocore.get_buffer(decoder)
-        print(f"{i} {result} {normalized_rms_ulab(buf):5.0f}")
+        print(f"{i} {result} {loudness(buf):5.0f}")
     print()
 
 

tests/circuitpython/issue9705.py.exp

@@ -1,16 +1,16 @@
 0 1     0
-1 1  4730
-2 1 27914
-3 1 28737
-4 1 29251
-5 1 29219
-6 1 28672
-7 1 28213
+1 1    25
+2 1   830
+3 1   880
+4 1   932
+5 1   892
+6 1   869
+7 1   839
 
 0 1     0
-1 1  4730
+1 1    25
 
 0 1     0
-1 1  4730
-2 1 27914
+1 1    25
+2 1   830