A system for improving speech intelligibility of an audio signal, comprises a hearing aid (10), a server (71), and an external device (50)—such as a smartphone or a tablet computer. The hearing aid has a short range transceiver. The server is accessible via the Internet, and has a Speech Recognition Engine converting speech into text. The external device has a short range transceiver for communication with said hearing aid, a second transceiver for providing a wireless data connection to said server via the Internet, means for handling a speech stream intended for the hearing aid, and a Text-To-Speech engine adapted to synthesize speech based on a string of text. The invention also provides a method of improving speech intelligibility of an audio signal.