fix: clamp shift perturbation for short audio instead of silently skipping

nemo/collections/asr/parts/preprocessing/perturb.py

@@ -438,10 +438,12 @@ def __init__(self, min_shift_ms=-5.0, max_shift_ms=5.0, rng=None):
 
     def perturb(self, data):
         shift_ms = random.uniform(self._min_shift_ms, self._max_shift_ms)
-        if abs(shift_ms) / 1000 > data.duration:
-            # TODO: do something smarter than just ignore this condition
-            return
+        max_shift_ms = data.duration * 1000
+        if abs(shift_ms) > max_shift_ms:
+            shift_ms = max(-max_shift_ms, min(shift_ms, max_shift_ms))
         shift_samples = int(shift_ms * data.sample_rate // 1000)
+        if shift_samples == 0:
+            return
         # logging.debug("shift: %s", shift_samples)
         if shift_samples < 0:
             data._samples[-shift_samples:] = data._samples[:shift_samples]

tests/collections/asr/test_preprocessing_segment.py

@@ -22,7 +22,7 @@
 import pytest
 import soundfile as sf
 
-from nemo.collections.asr.parts.preprocessing.perturb import NoisePerturbation, SilencePerturbation
+from nemo.collections.asr.parts.preprocessing.perturb import NoisePerturbation, ShiftPerturbation, SilencePerturbation
 from nemo.collections.asr.parts.preprocessing.segment import AudioSegment, select_channels
 
 
@@ -485,3 +485,48 @@ def test_audio_segment_trim_match(self, tmpdir, target_sr):
 
                 # Test
                 assert audio_segment_1 == audio_segment_2, f'trim setup {trim_setup}, loaded segments not matching'
+
+
+class TestShiftPerturbation:
+    sample_rate = 16000
+
+    def _make_audio_segment(self, duration_sec=1.0):
+        """Create a simple AudioSegment with a sine wave for testing."""
+        num_samples = int(duration_sec * self.sample_rate)
+        t = np.linspace(0, duration_sec, num_samples, dtype=np.float32)
+        samples = np.sin(2 * np.pi * 440 * t)
+        return AudioSegment(samples=samples, sample_rate=self.sample_rate)
+
+    def test_shift_perturbation_normal(self):
+        """Shift perturbation modifies audio when shift is within duration."""
+        perturb = ShiftPerturbation(min_shift_ms=-5.0, max_shift_ms=5.0)
+        segment = self._make_audio_segment(duration_sec=1.0)
+        original = segment.samples.copy()
+        perturb.perturb(segment)
+        assert segment.samples.shape == original.shape, "Audio length should not change"
+
+    def test_shift_perturbation_short_audio_not_skipped(self):
+        """Shift perturbation should clamp and apply shift for short audio, not silently skip."""
+        perturb = ShiftPerturbation(min_shift_ms=10.0, max_shift_ms=20.0)
+        duration_sec = 0.005  # 5ms — shorter than min_shift_ms
+        segment = self._make_audio_segment(duration_sec=duration_sec)
+        original = segment.samples.copy()
+        perturb.perturb(segment)
+        assert segment.samples.shape == original.shape, "Audio length should not change"
+
+    @pytest.mark.parametrize("duration_sec", [0.001, 0.01, 0.1, 1.0])
+    def test_shift_perturbation_preserves_length(self, duration_sec):
+        """Audio length must be preserved regardless of duration."""
+        perturb = ShiftPerturbation(min_shift_ms=-50.0, max_shift_ms=50.0)
+        segment = self._make_audio_segment(duration_sec=duration_sec)
+        original_len = len(segment.samples)
+        perturb.perturb(segment)
+        assert len(segment.samples) == original_len, "Shift perturbation must preserve audio length"
+
+    def test_shift_perturbation_zero_shift(self):
+        """When min and max shift are both 0, audio should be unchanged."""
+        perturb = ShiftPerturbation(min_shift_ms=0.0, max_shift_ms=0.0)
+        segment = self._make_audio_segment(duration_sec=0.5)
+        original = segment.samples.copy()
+        perturb.perturb(segment)
+        np.testing.assert_array_equal(segment.samples, original, "Zero shift should not modify audio")