From 3d7abfcb94fa7555bac6d806b05338edd857edf7 Mon Sep 17 00:00:00 2001
From: Todd Stephenson <71510807+toddstep@users.noreply.github.com>
Date: Fri, 18 Sep 2020 15:55:44 +0000
Subject: [PATCH 1/3] Add test for warning from create_fb_matrix

---
 .../functional/functional_cpu_test.py           | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/test/torchaudio_unittest/functional/functional_cpu_test.py b/test/torchaudio_unittest/functional/functional_cpu_test.py
index 96aac4e770..4fbe4d871e 100644
--- a/test/torchaudio_unittest/functional/functional_cpu_test.py
+++ b/test/torchaudio_unittest/functional/functional_cpu_test.py
@@ -21,6 +21,23 @@ class TestLFilterFloat64(Lfilter, common_utils.PytorchTestCase):
     device = torch.device('cpu')
 
 
+class TestCreateFBMatrix(common_utils.TorchaudioTestCase):
+    def test_no_warning_high_n_freq(self):
+        with pytest.warns(None) as w:
+            F.create_fb_matrix(288, 0, 8000, 128, 16000)
+        assert len(w) == 0
+
+    def test_no_warning_low_n_mels(self):
+        with pytest.warns(None) as w:
+            F.create_fb_matrix(201, 0, 8000, 89, 16000)
+        assert len(w) == 0
+
+    def test_warning(self):
+        with pytest.warns(None) as w:
+            F.create_fb_matrix(201, 0, 8000, 128, 16000)
+        assert len(w) == 1
+
+
 class TestComputeDeltas(common_utils.TorchaudioTestCase):
     """Test suite for correctness of compute_deltas"""
     def test_one_channel(self):

From 1dd8f0dd808b9f3cf635443712ab9582cc63b892 Mon Sep 17 00:00:00 2001
From: Todd Stephenson <71510807+toddstep@users.noreply.github.com>
Date: Fri, 18 Sep 2020 15:55:57 +0000
Subject: [PATCH 2/3] Warn if create_fb_matrix produces a column whose weights
 are all zeros

---
 torchaudio/functional.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/torchaudio/functional.py b/torchaudio/functional.py
index 4e8e62848e..8a7b3babfb 100644
--- a/torchaudio/functional.py
+++ b/torchaudio/functional.py
@@ -313,6 +313,13 @@ def create_fb_matrix(
         enorm = 2.0 / (f_pts[2:n_mels + 2] - f_pts[:n_mels])
         fb *= enorm.unsqueeze(0)
 
+    if (fb.max(dim=0).values == 0.).any():
+        warnings.warn(
+            "At least one mel filterbank has all zero values."
+            "The value for `n_mels` ({}) may be set too high."
+            "Or, the value for `n_freqs` ({}) may be set too low.".format(n_mels, n_freqs)
+        )
+
     return fb
 
 

From 45fdc398c994f1eb5711f83a92bc35dd7d5bbd1a Mon Sep 17 00:00:00 2001
From: Todd Stephenson <71510807+toddstep@users.noreply.github.com>
Date: Fri, 18 Sep 2020 18:24:19 +0000
Subject: [PATCH 3/3] Clean up formatting of Mel FB warning message

---
 torchaudio/functional.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/torchaudio/functional.py b/torchaudio/functional.py
index 8a7b3babfb..a6514c79f2 100644
--- a/torchaudio/functional.py
+++ b/torchaudio/functional.py
@@ -315,9 +315,9 @@ def create_fb_matrix(
 
     if (fb.max(dim=0).values == 0.).any():
         warnings.warn(
-            "At least one mel filterbank has all zero values."
-            "The value for `n_mels` ({}) may be set too high."
-            "Or, the value for `n_freqs` ({}) may be set too low.".format(n_mels, n_freqs)
+            "At least one mel filterbank has all zero values. "
+            f"The value for `n_mels` ({n_mels}) may be set too high. "
+            f"Or, the value for `n_freqs` ({n_freqs}) may be set too low."
         )
 
     return fb