def split_df(df):
    """
    This will split a VOiCES index dataframe by microphone and distractor type

    Inputs:
        df - A pandas dataframe representing the index file of the dataset,
            with the default columns of VOiCES index files.
    Outputs:
        df_dict - A dictionary where keys are (mic,distractor type) and values
            are dataframes corresponding to slices of df with that mic and
            distractor value pair.
    """
    distractor_values =df['distractor'].unique()
    mic_values = df['mic'].unique()
    df_dict = {}
    for m_val in mic_values:
        for dist_val in distractor_values:
            sub_df = df[(df['mic']==m_val) & (df['distractor']==dist_val)]
            df_dict[(m_val,dist_val)]=sub_df
    return df_dict