src/transformers/models/mctct/feature_extraction_mctct.py/MCTCTFeatureExtractor/_normalize_one
class MCTCTFeatureExtractor:    def _normalize_one(self, x, input_length, padding_value):
        # make sure we normalize float32 arrays
        if self.normalize_means:
            mean = x[:input_length].mean(axis=0)
            x = np.subtract(x, mean)
        if self.normalize_vars:
            std = x[:input_length].std(axis=0)
            x = np.divide(x, std)

        if input_length < x.shape[0]:
            x[input_length:] = padding_value

        # make sure array is in float32
        x = x.astype(np.float32)

        return x