Reports on Progress:

Quality Adviser

Quality Adviser is a multichannel audio quality expert system designed using the data base of subjective responses obtained in the course of the project. It has been design to assist broadcasting engineers in some decisions. For example, what decision should audio engineers make in case of broadcasting multichannel audio under highly restricted transmission conditions (e.g. broadcasting over the internet)? Should they decide to limit the bandwidth of individual channels of the broadcasted audio material or should they sacrifice spatial quality by down-mixing the original multichannel audio material to a lower number of broadcasted audio channels? The Quality Adviser can be used in order to find the answer to this difficult question.

The figure below shows the graphical user interface of the Quality Adviser. In this example the Quality Adviser was used to solve the following problem.


What to do in order to gracefully reduce the effective bandwidth of an uncompressed multichannel audio material down to two effective channels (equivalent of two full bandwidth channels)? The programme material will be broadcast in the audio-visual format (picture will accompany audio). It is known that audio programme material contains an F-B spatial scene. There is no dialogue in the centre channel. The answer should take into account averaged audio quality across different listening position.

figure: Spat


The Quality Adviser displays four best solutions in the descending order. In this example the best solution is to broadcast a full bandwidth stereo down-mix (Advice 1). This should result in a Good audio quality. Another possible solution is to broadcast all channels; however front left and right channels should be band-limited to 10 kHz, the centre channel to 13 kHz, and the surround channels to 3.5 kHz (Advice 2). This solution should provide the listener with a Fair audio quality. The next possible solution is to broadcast front and right channels band-limited to 13 kHz, the centre channel limited to 7 kHz and the surround channels limited to 3.5 kHz (Advice 3). It is predicted that this solution will provide the listener with a Fair audio quality. The last displayed advice is to broadcast all channels band-limited down to 8 kHz (Advice 4). However, it is predicted that this solution will result in the quality between Fair and Poor.

An important question that one may ask looking at the Quality Adviser is how reliable it is. Another possible question is: How can we be sure that the results obtained from the Quality Adviser really match the actual responses what the real listeners? In order to find the answer click here.