add window process func

third_party/paddle_audio/frontend/common.py

 import paddle
 import numpy as np
-from typing import Tuple
+from typing import Tuple, Optional
 
 
 # https://github.com/kaldi-asr/kaldi/blob/cbed4ff688/src/feat/feature-window.cc#L109
@@ -32,7 +32,7 @@ def hamm_window(frame_len:int) -> np.ndarray:
         win[i] = 0.54 - 0.46 * np.cos(a * i)
     return win
 
-def get_window(wintype:str, winlen:int) -> np.ndarray:
+def get_window(wintype:Optional[None, str], winlen:int) -> np.ndarray:
     # calculate window
     if not wintype or wintype == 'rectangular':
         window = np.ones(winlen)

third_party/paddle_audio/frontend/kaldi.py

@@ -68,6 +68,29 @@ def frames(x: Tensor,
     return frames, num_frames
 
 
+def do_dither(signal, dither_value=1.0):
+    signal += paddle.normal(shape=signal.shape) * dither_value
+    return signal
+    
+    
+def do_remove_dc_offset(signal):
+    signal -= paddle.mean(signal)
+    return signal
+
+
+def do_preemphasis(signal, coeff=0.97):
+    """perform preemphasis on the input signal.
+
+    :param signal: The signal to filter.
+    :param coeff: The preemphasis coefficient. 0 is no filter, default is 0.95.
+    :returns: the filtered signal.
+    """
+    return paddle.concat([
+        (1-coeff)*signal[0:1],
+        signal[1:] - coeff * signal[:-1]
+    ])
+
+
 class STFT(nn.Layer):
     """A module for computing stft transformation in a differentiable way.