Matrixing of bit rate reduced audio signals

The effects of the combined use of matrixing and bit rate reduction of audio signals are discussed. Bit rate reduction introduces quantization noise in the audio signal. This noise remains unnoticed by the human ear because of the masking caused by the audio signal. However, when matrixing is applied to such a quantized signal the audio part and the quantization noise can be separated and routed to different loudspeakers. This may result in the appearance of audible artifacts. A method is presented by which bit rate reduced audio signals can be matrixed without causing such artifacts to occur. The first step is to apply prequantization before the enmatrixing. The second step is to adapt the masking signal input to the encoder. Application is in HDTV, where a surround sound signal should be transmitted in a compatible way with the existing stereo format. Compatible transmission is possible by the combined use of bit rate reduction and matrixing. In the proposed scheme the resulting signals will remain free from audible artifacts