<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def convert_to_wav(self, filename):
 """ Uses sox cmdline tool, to convert audio file to .wav Note: for testing, use - http://www.text2speech.org/, with American Male 2 for best results """

        temp_filename = '{0}.wav'.format(self.temp_filename())
        self.run(['sox', '-G', '-c', '1', filename, temp_filename])
        return temp_filename