Circuit Arrangement for Processing, Transmitting, and Acoustically Reproducing Digitized Audio-Frequency Signals

The present invention relates to a circuit arrangement for processing, transmitting, and acoustically reproducing digitized audio-frequency signals which are processed in a signal processor together with digital control signals such as volume, tone, stereo balance, etc., and pass through an infrared transmission link whose receiver and a following power amplifier are incorporated in a loudspeaker box. The block diagram of such a circuit arrangement was made accessible to the public by the applicant at the September 1981 Berlin International Radio and Television Exhibition in the form of a chart. The infrared transmission link consisted of an infrared transmitter, an infrared receiver, and an optical-fiber cable interconnecting the transmitter and the receiver. As the infrared receiver and the following power amplifier are disposed within the loudspeaker box, this arrangement was called an "active" loudspeaker box ("active box").

The fiber-optic infrared transmission link has a certain disadvantage in that it limits the freedom to arrange the components of an audio system.

It is an object of the invention to provide a circuit arrangement such that the active boxes can be arranged freely from the remainder of the system. The invention utilizes wireless infrared sound transmission as is known per se in audio equipment installed for the hard of hearing in large assembly rooms, but modifies this principle of transmission with respect to the processing of audio-frequency signals digitized in a protected code. Such signals are present, for example, on the so-called digital disk; they are digitized using the so-called Cross Interleave Reed Solomon code (CIR code), cf. a publication by Sony Corp. /N.V. Philips entitled "Compact Disc Digital Audio", September, 1980.

The advantages of the invention lie directly in the solution of the problem but also in the fact that all signal processing operations can be performed with digital integrated circuits which are stable in operation, digitally controllable, insensitive to interference, and programmable. Furthermore, during the design of such digital systems, the operation and behaviour of the circuits to be implemented can be fully simulated by computers. A particular advantage of the invention follows from the fact that the digital data can reach the active boxes; on the infrared transmission link, they are modulated onto an RF carrier, which can be done by using conventional techniques, such as frequency-shift keying or similar modulation methods.

The invention will now be explained in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the principle underlying the invention;

FIG. 2 shows a development of the invention for the connection of additional AF signal sources to the circuit arrangement of FIG. 1;

FIG. 3 is a block diagram of a modification of the invention in which the order of the individual subcircuits is different from that in the arrangement of FIG. 1, and

FIG. 4 shows the connection of additional AF signal sources to the arrangement of FIG. 3.

The block diagram of FIG. 1 shows the digital-signal source D, which encodes the audio-frequency signals, i.e., signals coming from a microphone, for example, in a protected code, i.e., in a redundant code which permits not only error detection but also error correction, such as the above-mentioned CIR code.

The output of the digital-signal source D is connected to the input of the code-conversion/error-correction processor CP, which performs the necessary error correction and converts the code of the source D to a, e.g, nonredundant code. Further processing of the digitized audio-frequency signals then takes place on the basis of this code in the signal processor SP, to which the output signals of the code-conversion/error-correction processor CP are transferred in parallel, as are the digital control signals from the remote-control receiver FE, which are transmitted to the latter from the remote-control transmitter FS. The digital control signals may also, of course, come from any other digital control unit that may be associated with the circuit arrangement according to the invention.

In the signal processor SP, the digital control signals are combined with or added to the digitized audio-frequency signals in the known manner to control corresponding values, such as volume, tone, stereo balance, base width, etc. The output signals of the signal processor SP, which are now delivered in serial form, are fed to the RF modulator M, which, in turn, drives the transmitter S of the wireless infrared transmission link I.

At least one loudspeaker box B is disposed at the receiving end of the infrared transmission link I; FIG. 1 shows only two boxes B, Bm of the plurality of boxes that are possible. Each loudspeaker box B, Bm contains the reciever E of the infrared transmission link I, the RF demodulator DM, the digital-to-analog converter DA, the power amplifier V, and the loudspeaker L, which are connected in series with respect to the signal flow in this order.

If several loudspeaker boxes B, Bm are associated with a single transmitter S, control signals differing from those for the other loudspeaker boxes may be provided for each box, which are again fed to the signal processor SP. With several loudspeaker boxes and a single transmitter S it is also necessary to assign to each loudspeaker box its own carrier frequency of the RF modulator M.

FIG. 2 shows a development of the basic arrangement of FIG. 1 in which not only the digital-signal source D but also other audio-frequency signal sources Q, Qn can be connected. To make this possible, a multiplexer MX, to which the signals from the additional audio-frequency signal sources Q, Qn are fed through the analog-to-digital converter AD, must be inserted between the code-conversion/error-correction processor CP and the signal processor SP. Advantageously, the multiplexer MX is controlled by the control-signal source, i.e., the remote-control receiver FE, for example. The development of FIG. 2 thus makes it possible, for example, to not only play digital disks in an audio system but also operate the system with further audio-frequency signal sources of the usual kind, such as a cassette recorder, a radio or a conventional record player.

FIG. 3 shows a principle in which the order of the individual subcircuits of the circuit arrangement according to the invention has been changed so that a considerable improvement is obtained on the basic arrangement of FIG. 1 with respect to error correction. In the arrangement of FIG. 3, the code-conversion/error-correction processor CP is incorporated in the loudspeaker box B', B'm. This has the essential advantage that even errors arising on the wireless infrared transmission link I are correctable. The subcircuits in the arrangement of FIG. 3 are so arranged that the digital-signal source D drives the RF modulator M direct, which is also fed with the digital control signals coming, for example, from the receiver FE of a remote-control facility. The RF modulator M drives the transmitter S of the wireless infrared transmission link I. At the receiving end of the link, e.g., within the loudspeaker box B', the following subcircuits are connected in series with respect to the signal flow in this order: receiver E, RF demodulator DM, code-conversion/error-correction processor CP, signal processor SP, digital-to-analog converter DA, power amplifier V, and loudspeaker L. In the arrangement of FIG. 3, too, it is possible, of course, to drive a plurality of loudspeaker boxes B', B'm with a single transmitter S, in which case each loudspeaker box requires a carrier frequency of its own. Likewise, separate control signals as described in connection with FIG. 2 may be provided for the individual loudspeaker boxes B', B'm.

FIG. 4 shows in analogy to FIG. 2 that the arrangement of FIG. 3, too, permits the connection of additional audio-frequency signal sources Q, Qn via the analog-to-digital converter AD and the multiplexer MX.

The need to assign to each active box a carrier frequency of its own is eliminated if signals for two or more loudspeaker boxes are transmitted on an RF carrier, e.g., on a time-division multiplex basis. In the various receiving circuits, the respective desired signals are then extracted from the overall data stream.