Add warning for non-integer resampling frequencies (pytorch#1490)

test/torchaudio_unittest/functional/functional_impl.py

@@ -9,7 +9,7 @@
 from parameterized import parameterized
 from scipy import signal
 
-from torchaudio_unittest.common_utils import TestBaseMixin, get_sinusoid, nested_params
+from torchaudio_unittest.common_utils import TestBaseMixin, get_sinusoid, nested_params, get_whitenoise
 
 
 class Functional(TestBaseMixin):
@@ -259,6 +259,31 @@ def test_mask_along_axis_iid_preserve(self, mask_param, mask_value, axis):
 
             self.assertEqual(specgrams, specgrams_copy)
 
+    def test_resample_no_warning(self):
+        sample_rate = 44100
+        waveform = get_whitenoise(sample_rate=sample_rate, duration=0.1)
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            F.resample(waveform, float(sample_rate), sample_rate / 2.)
+        assert len(w) == 0
+
+    def test_resample_warning(self):
+        """resample should throw a warning if an input frequency is not of an integer value"""
+        sample_rate = 44100
+        waveform = get_whitenoise(sample_rate=sample_rate, duration=0.1)
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            F.resample(waveform, sample_rate, 5512.5)
+        assert len(w) == 1
+
+
+class FunctionalComplex(TestBaseMixin):
+    complex_dtype = None
+    real_dtype = None
+    device = None
+
     @nested_params(
         [0.5, 1.01, 1.3],
         [True, False],

torchaudio/functional/functional.py

@@ -1395,6 +1395,19 @@ def resample(
 
     assert orig_freq > 0.0 and new_freq > 0.0
 
+    if not (int(orig_freq) == orig_freq and int(new_freq) == new_freq):
+        warnings.warn(
+            "Non-integer frequencies are being cast to ints and may result in poor resampling quality "
+            "because the underlying algorithm requires an integer ratio between `orig_freq` and `new_freq`. "
+            "Using non-integer valued frequencies will throw an error in the next release. "
+            "To work around this issue, manually convert both frequencies to integer values "
+            "that maintain their resampling rate ratio before passing them into the function "
+            "Example: To downsample a 44100 hz waveform by a factor of 8, use "
+            "`orig_freq=8` and `new_freq=1` instead of `orig_freq=44100` and `new_freq=5512.5` "
+            "For more information or to leave feedback about this change, please refer to "
+            "https://github.com/pytorch/audio/issues/1487."
+        )
+
     orig_freq = int(orig_freq)
     new_freq = int(new_freq)
     gcd = math.gcd(orig_freq, new_freq)