| 摘要 |
A coder for incorporating extra information in the form of an auxiliary signal in a digital audio signal having a predetermined format as well as a decoder for extracting this extra information from this digital signal, whilst the digital audio signal having the predetermined format is divided into frequency sub-bands, in which on the basis of psychoacoustic qualities of the human auditory system a relatively large amount of quantization noise is permissible, and the samples in each of these sub-bands are quantized relatively coarsely according to a preset criterion, whilst the quantized sub-band signals are summed with samples of the auxiliary signal, whose maximum amplitude is always smaller than a half quantization step of the relevant sample of the main signal; the summed sub-band signals are then reconstructed to a signal covering the entire frequency band, converted into a digital signal having the predetermined format and recorded or transmitted. In an unmodified receiver or reproducing device the original digital audio signal can be reproduced in a conventional way whereas the auxiliary signal remains masked. In a receiver or reproducing device comprising a decoder the signal is again divided into an equal number of frequency sub-hands in a way corresponding to that used in the coder and they are re-quantized according to the criterion applied in the coder. By subtracting per sub-band the quantized signal from the non-quantized signal, sub-bands of the auxiliary signal are formed, which are reconstructed into a replica of the complete original auxiliary signal. The coder can be employed in a device for recording a digital signal on the record carrier. Thus, record carriers can be obtained which are provided with a copy inhibit code and which are thus protected against unauthorized copying. If a signal containing such a copy inhibit code is to be recorded again this inhibit code is detected and recording can be inhibited, the signal to be recorded can be distorted seriously and/or the presence of the copy inhibit code can be signalled. |
