Add support for 24-bit signed LPCM wav in sox_io backend (#1389) (#1398)

Co-authored-by: Isaac Seessel <iseessel@oberlin.edu>

Author: vincentqb

test/torchaudio_unittest/backend/sox_io/load_test.py

@@ -42,6 +42,49 @@ def assert_wav(self, dtype, sample_rate, num_channels, normalize, duration):
         assert sr == sample_rate
         self.assertEqual(data, expected)
 
+    def assert_24bit_wav(self, sample_rate, num_channels, normalize, duration):
+        """ `sox_io_backend.load` can load 24-bit signed PCM wav format. Since torch does not support the ``int24`` dtype,
+        we implicitly cast the resulting tensor to the ``int32`` dtype.
+
+        It is not possible to use #assert_wav method above, as #get_wav_data does not support
+        the 'int24' dtype. This is because torch does not support the ``int24`` dtype.
+        Hence, we must use the following workaround.
+
+         x
+         |
+         |    1. Generate 24-bit wav with Sox.
+         |
+         v    2. Convert 24-bit wav to 32-bit wav with Sox.
+      wav(24-bit) ----------------------> wav(32-bit)
+         |                                   |
+         | 3. Load 24-bit wav with torchaudio| 4. Load 32-bit wav with scipy
+         |                                   |
+         v                                   v
+        tensor ----------> x <----------- tensor
+                       5. Compare
+
+        # Underlying assumptions are:
+        # i. Sox properly converts from 24-bit to 32-bit
+        # ii. Loading 32-bit wav file with scipy is correct.
+        """
+        path = self.get_temp_path('1.original.wav')
+        ref_path = self.get_temp_path('2.reference.wav')
+
+        # 1. Generate 24-bit signed wav with Sox
+        sox_utils.gen_audio_file(
+            path, sample_rate, num_channels,
+            bit_depth=24, duration=duration)
+
+        # 2. Convert from 24-bit wav to 32-bit wav with sox
+        sox_utils.convert_audio_file(path, ref_path, bit_depth=32)
+        # 3. Load 24-bit wav with torchaudio
+        data, sr = sox_io_backend.load(path, normalize=normalize)
+        # 4. Load 32-bit wav with scipy
+        data_ref = load_wav(ref_path, normalize=normalize)[0]
+        # 5. Compare
+        assert sr == sample_rate
+        self.assertEqual(data, data_ref, atol=3e-03, rtol=1.3e-06)
+
     def assert_mp3(self, sample_rate, num_channels, bit_rate, duration):
         """`sox_io_backend.load` can load mp3 format.
 
@@ -50,7 +93,7 @@ def assert_mp3(self, sample_rate, num_channels, bit_rate, duration):
 
          x
          |
-         | 1. Generate mp3 with Sox
+         |    1. Generate mp3 with Sox
          |
          v    2. Convert to wav with Sox
         mp3 ------------------------------> wav
@@ -61,7 +104,7 @@ def assert_mp3(self, sample_rate, num_channels, bit_rate, duration):
         tensor ----------> x <----------- tensor
                        5. Compare
 
-        Underlying assumptions are;
+        Underlying assumptions are:
         i. Conversion of mp3 to wav with Sox preserves data.
         ii. Loading wav file with scipy is correct.
 
@@ -213,6 +256,15 @@ def test_wav(self, dtype, sample_rate, num_channels, normalize):
         """`sox_io_backend.load` can load wav format correctly."""
         self.assert_wav(dtype, sample_rate, num_channels, normalize, duration=1)
 
+    @parameterized.expand(list(itertools.product(
+        [8000, 16000],
+        [1, 2],
+        [False, True],
+    )), name_func=name_func)
+    def test_24bit_wav(self, sample_rate, num_channels, normalize):
+        """`sox_io_backend.load` can load 24bit wav format correctly. Corectly casts it to ``int32`` tensor dtype."""
+        self.assert_24bit_wav(sample_rate, num_channels, normalize, duration=1)
+
     @parameterized.expand(list(itertools.product(
         ['int16'],
         [16000],

torchaudio/backend/sox_io_backend.py

@@ -73,6 +73,7 @@ def load(
 
             * 32-bit floating-point
             * 32-bit signed integer
+            * 24-bit signed integer
             * 16-bit signed integer
             * 8-bit unsigned integer (WAV only)
 
@@ -92,10 +93,11 @@ def load(
     The samples are normalized to fit in the range of ``[-1.0, 1.0]``.
 
     When the input format is WAV with integer type, such as 32-bit signed integer, 16-bit
-    signed integer and 8-bit unsigned integer (24-bit signed integer is not supported),
-    by providing ``normalize=False``, this function can return integer Tensor, where the samples
-    are expressed within the whole range of the corresponding dtype, that is, ``int32`` tensor
-    for 32-bit signed PCM, ``int16`` for 16-bit signed PCM and ``uint8`` for 8-bit unsigned PCM.
+    signed integer, 24-bit signed integer, and 8-bit unsigned integer, by providing ``normalize=False``,
+    this function can return integer Tensor, where the samples are expressed within the whole range
+    of the corresponding dtype, that is, ``int32`` tensor for 32-bit signed PCM,
+    ``int16`` for 16-bit signed PCM and ``uint8`` for 8-bit unsigned PCM. Since torch does not
+    support ``int24`` dtype, 24-bit signed PCM are converted to ``int32`` tensors.
 
     ``normalize`` parameter has no effect on 32-bit floating-point WAV and other formats, such as
     ``flac`` and ``mp3``.

torchaudio/csrc/sox/utils.cpp

@@ -118,15 +118,16 @@ caffe2::TypeMeta get_dtype(
     switch (encoding) {
       case SOX_ENCODING_UNSIGNED: // 8-bit PCM WAV
         return torch::kUInt8;
-      case SOX_ENCODING_SIGN2: // 16-bit or 32-bit PCM WAV
+      case SOX_ENCODING_SIGN2: // 16-bit, 24-bit, or 32-bit PCM WAV
         switch (precision) {
           case 16:
             return torch::kInt16;
+          case 24: // Cast 24-bit to 32-bit.
           case 32:
             return torch::kInt32;
           default:
             throw std::runtime_error(
-                "Only 16 and 32 bits are supported for signed PCM.");
+                "Only 16, 24, and 32 bits are supported for signed PCM.");
         }
       default:
         // default to float32 for the other formats, including