MP3-like approach to improve sound quality of telephones and video conferencing
By Darren Quick
May 30, 2011
Engineers from one of the main players responsible for the development of the MP3 codec, the Fraunhofer Institute for Integrated Circuits IIS, have developed a new audio coding technology that aims to provide telephone calls and video conferences with sound quality approaching that of direct communication, while at the same time cutting delay times that often sees both speakers talking over each other. The solution is called Enhanced Low Delay Advanced Audio Coding - or AAC-ELD - and researchers claim it results in long-distance communications that appear almost as if the participants are sitting across from each other.
The MP3 codec uses a lossy compression algorithm that essentially reduces the accuracy of certain parts of sound that are considered beyond the ability of most people to hear. The result is much smaller audio files that can be transmitted much faster while still sounding fairly faithful to the original audio. However, since the audio first needs to be encoded and then decoded at the listener's end, the Fraunhofer engineers faced a bit of a balancing act in developing something similar for interactive communications.
"The algorithm requires a certain amount of time to encode the data and to decode it again at the other end of the line. The process requires data that is still in the future, as it must wait for the data to arrive. This can result in a situation where interactive communication is very difficult," explains Markus Schnell.
After several years of trying to strike an optimum balance that gave the best possible quality with the shortest possible delay, the team decided on an algorithm that produced a delay of only about 15 milliseconds. The engineers say that is this timespan the algorithm manages to reduce the audio data to less than one-thirtieth of its original size without a major loss in sound quality.
The Fraunhofer team says the improved speech transmission offered by AAC-ELD could have applications not only for telephone calls, but also for video conferencing applications used on mobile devices and real-time chat during games.