Coder for incorporating an auxiliary information signal in a digital audio signal, decoder for recovering such signals from the combined signal, and record carrier having such combined signal recorded thereon

A decoder for a received digital audio signal which is an encoded form of an original digital audio signal, the received signal having a plurality (P) of successive frequency sub-bands which respectively include quantized samples of the original digital audio signal, one or more of said sub-bands also including samples of an auxiliary signal, each auxiliary signal sample being below the level of the quantizing step applicable to the quantized audio signal sample in the corresponding sub-band;

• said decoder comprising:
• analysis filter means for analyzing the received signal into said P sub-bands so as to derive P sub-band samples thereof;
• means for quantizing the respectively sub-band samples using a quantizing step in each sub-band the same as that applicable to the quantized sample of the original audio signal in such sub-band;
• means for subtracting the quantized signal sample in each sub-band from the received signal sample in such sub-band so as to thereby derive a difference signal sample for each sub-band, such sub-band difference signal samples being samples of said auxiliary signal in such sub-bands;
• means for amplifying the respective sub-band samples of the auxiliary signal by amounts corresponding to the quantizing steps applicable to the respective sub-bands;
• and
• synthesis filter means for combining the amplified sub-band samples of the auxiliary signal so as to thereby reconstruct said auxiliary signal.

Apparatus for recording a digital audio signal having a predetermined data format on a record carrier, comprising:

• coding means including
• analysis filter means for analyzing the frequency band of the audio signal into a plurality P of successive sub-bands so as to derive P audio signal samples in such sub-bands, the sub-bands corresponding to critical frequency bands of the human auditory system for masking of noise in the presence of sounds in such frequency bands;
• means for quantizing the respective sub-band samples in accordance with quantizing steps based on a predetermined quantization criterion so as to derive P quantized sub-band samples, the quantizing step for each sub-band being adapted in accordance with the maximum amplitude of the signal sample in such sub-band;
• and
• signal combining means including synthesis filter means coupled to said analysis filter means and to said quantizing means, said signal combining means being adapted to derive sub-band difference signals corresponding to the difference between each sub-band signal sample and the quantized signal sample in such sub-band and to combine such difference signals into an auxiliary signal;
• a recording unit for receiving the P quantized sub-band signal samples and recording them on said record carrier;
• and
• detecting means coupled to said signal combining means and responsive to the auxiliary signal produced thereby to supply a control signal to said recording unit, said control signal signifying that the received audio signal is protected against recording thereof.

A record carrier having recorded thereon a compound signal comprising:

• a digital audio signal in the form of a plurality P of sub-band samples thereof in P successive frequency sub-bands, such sub-band samples having been quantized in accordance with quantizing steps applicable to the respective sub-bands;
• and
• an auxiliary signal in the form of sub-band samples thereof in one or more of said sub-bands, the amplitude of the auxiliary signal sample in any sub-band being below the level of the quantizing step applicable to the audio signal sample in such sub-band;
• whereby upon audible reproduction of sound corresponding to the recorded compound signal the auxiliary signal sub-band samples thereof will be substantially inaudible, only the audio signal sub-band samples thereof audibly contributing to the resulting sound.