add image for specaugment.

Author: vincentqb

docs/source/_static/img/specaugment-freq.jpg

@@ -821,6 +821,9 @@ def forward(self, specgram: Tensor, mask_value: float = 0.) -> Tensor:
 class FrequencyMasking(_AxisMasking):
     r"""Apply masking to a spectrogram in the frequency domain.
 
+    In the image below, a frequency band has been masked on a spectrogram.
+    .. image:: _static/img/specaugment-freq.jpg
+
     Args:
         freq_mask_param (int): maximum possible length of the mask.
             Indices uniformly sampled from [0, freq_mask_param).
@@ -835,6 +838,9 @@ def __init__(self, freq_mask_param: int, iid_masks: bool = False) -> None:
 class TimeMasking(_AxisMasking):
     r"""Apply masking to a spectrogram in the time domain.
 
+    In the image below, a time band has been masked on a spectrogram.
+    .. image:: _static/img/specaugment-time.jpg
+
     Args:
         time_mask_param (int): maximum possible length of the mask.
             Indices uniformly sampled from [0, time_mask_param).