Abstract:
A CD player, including a CD drive, which receives a CD and reads compressed digital audio data recorded thereon, and an integrated circuit chip, which decompresses the compressed data and produces a non-compressed audio output. Preferably, the data are compressed by MPEG compression, most preferably by MPEG Layer-3 compression, so that the data are compressed approximately 12-fold, and the CD contains over 800 minutes of high-quality stereo sound recording.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of audio recording and playing, and specifically to audio compact disks players. 
     BACKGROUND OF THE INVENTION 
     Compact disks (CDs) are storage devices for audio signals encoded as digital data. Audio CD players convert the CD digital data to analog data, which are directly reproducible as audio signals. 
     Conventional CDs contain digitized audio data, generally without any data reduction or compression. They are typically capable of storing 650 megabytes of data, which is roughly equivalent to 74 minutes of high-quality standard audio transmission. The conventional audio CD is relatively impervious to normal usage, user-friendly, inexpensive to manufacture, and produces high-quality sound. 
     The Moving Picture Experts Group (MPEG) has defined encoding standards for moving pictures and audio signals. MPEG encoding compresses signals using encoding algorithms that produce a slightly less than exact reproduction of the picture, or audio signal, but in a way that is normally largely unnoticeable to the human senses. The MPEG standards for encoding audio signals are known as MPEG Audio Layers-1, -2 and -3, with each layer being progressively more compressed than that before it. Layer-1 compresses digital audio data approximately 4-fold; Layer-2, 6- to 8-fold; and Layer-3, 10- to 12-fold. Whereas uncompressed analog-to-digital encoding requires nearly 10 megabytes of data for 1 minute of high-quality stereo sound, with MPEG Layer-3 encoding, the same 1 minute of high-quality stereo sound requires less than 1 megabyte of data. 
     MPEG encoding is used for visual and video encoding, for example, in DVDs (Digital Video Disks), which are viewable on MPEG-enabled DVD video players. Fraunhofer Gesellschaft IIS-A, of Erlangen, Germany, offers MPEG-encoded audio/visual CD-ROMs designed for use with a personal computer having a sufficiently powerful CPU and suitable decoding software. MPEG Layer-3 audio encoding is also available for use in computers, network-based radio, and other applications that require large audio signal data bases. 
     To date MPEG compression and decompression require the use of a computer. For on-line, real-time play, particularly of MPEG Layer-3, which is relatively computation-intensive, a powerful computer, based at least on an Intel Pentium MMX processor, for example, is generally needed. Consequently, MPEG audio compression has not been applied to home entertainment or portable audio devices. 
     European Patent Application EP 0786774 describes a digital portable stereo headphone player for recording and playback of compressed audio data on a mini-disk. The player includes a compression/expansion circuit, but no details of this circuit are described. The player is complex and appears to have many of the features of a personal computer system. 
     European Patent Application EP 0772192 describes optical disk playback apparatus, which is capable of receiving disks that include either compressed or non-compressed audio data. If a disk including compressed data is received, the apparatus converts the data to non-compressed data. 
     SUMMARY OF THE INVENTION 
     It is an object of some aspects of the present invention to provide a personal audio device that can play audio CDs having extended playing time, preferably at least 800 minutes of playing time. 
     It is a further object of some aspects of the present invention to provide a system for producing extended-play audio CDs for home and mobile use, preferably using standard-size (12 cm diameter), widely available CD media. 
     In some preferred embodiments of the present invention, a CD player includes an integrated circuit chip, referred to herein as an MPEG decoder chip, or as an MPEG decompression chip, to decode compressed, MPEG-encoded audio data and read it as digital audio signals. The player receives long-play CDs including digital audio data that have been compressed according to the MPEG standard. The compressed data are read from the CD and passed to the chip, which decodes the data and outputs a stream of standard, uncompressed CD audio data, thereby enabling real-time, on-demand use of MPEG-encoded audio CDs without the necessity of a large and costly computing circuitry. 
     Preferably, the encoded audio data are compressed at least 4-fold, more preferably at least 8-fold, using MPEG Layer-1 or Layer-2 encoding, respectively. Most preferably, the data are compressed approximately 12-fold, based on the level of compression that is typically achieved using MPEG Layer-3 audio compression. The audio player is thus capable of receiving and playing long-play CDs including 12 times the conventional 74 minutes, or approximately 888 minutes (14.8 hours) of high-quality stereo music or voice recording. 
     Preferably, the MPEG decoder chip comprises a custom or application-specific integrated circuit, which is fabricated with firmware capability to decompress MPEG Layer-3 encoded audio data in real time. MPEG decoding algorithms are known in the art, but are typically implemented in software using general-purpose computer processors. The CD player of the present invention may include such a general-purpose processor, but those skilled in the art of integrated circuits will appreciate that a custom integrated circuit may be designed and fabricated to implement the MPEG decoding more efficiently and at a lower production cost than the general-purpose processor. 
     In one preferred embodiment of the present invention, the CD player is used as a component of a home entertainment system. In other preferred embodiments, the MPEG decoder chip is installed in a mobile CD player, for example, a personal portable CD or an automobile CD player. The present invention is particularly advantageous in these mobile applications, since it relieves the user of the need to carry around a large number of short-play (74 minute) CDs. Replacing multiple short-play CDs with one or a few long-play CDs, will also save on storage space in the home, office or vehicle. The CD player, be it the mobile or home entertainment version, is preferably equipped with all the common features and functions of a standard CD player, such as play, stop, pause, forward, rewind, display of track numbers, display of elapsed playing time, etc. 
     In other preferred embodiments of the present invention, a CD recording system comprises two CD drives: a read drive and a write drive. The read drive receives and reads conventional, non-compressed audio CDs. Data read by the read drive (either entire CDs or specific track(s) as selected by the user) are compressed, preferably using MPEG audio encoding, most preferably MPEG Layer-3. The compressed data are then written onto a recordable CD in the write drive, thus enabling 888 minutes (14.8 hours) of high-quality stereo sound to be recorded on a conventional CD, which normally would hold only 74 minutes of sound. The compression is preferably performed by an MPEG Layer-3 encoder chip, similar in principle to the decoder chip described above. 
     By using MPEG Layer-3 encoding, the system can condense the entire contents of as many as 12 conventional fully-recorded CDs onto a single, long-playing CD. (In fact, since commercially-recorded CDs are usually not recorded to their full 74 minute capacity, but rather to about 80% capacity, it may be possible to condense up to 15 conventional CDs onto a single long-playing CD.) A user of the recording system can record audio segments from the conventional CDs onto the long-playing CD in any desired sequence and combination. The long-playing CD produced in this manner is particularly suited for use in the CD player described above, but can also be used in a computer CD drive, for example, using software decompression and an appropriate computer sound-card and speakers to play back the recorded audio. 
     Alternatively, the CD recording system may comprise only a single read/write CD drive, along with a fixed mass-memory device, such as a magnetic hard disk. In this case, the conventional CDs, on which non-compressed audio data are recorded, are first inserted one by one into the drive. The audio data are read from the CDs, compressed, preferably using MPEG audio compression, most preferably MPEG Layer-3 encoding, then temporarily stored in the mass-memory device. Then the recordable CD is inserted into the same read/write CD drive, and the stored, compressed data from the mass-memory device are recorded on the CD. 
     While preferred embodiments of the present invention are based on MPEG audio compression, and particularly MPEG Layer-3 compression, it will be appreciated that the principles of the present invention may also be applied to produce audio players and recording systems based on other compression schemes, including MPEG audio Layer-4 encoding currently under development. 
     There is therefore provided, in accordance with a preferred embodiment of the present invention, a CD player, including: 
     a CD drive, which receives a CD and reads compressed digital audio data recorded thereon; and 
     an integrated circuit chip, which decompresses the compressed data and produces a non-compressed audio output. 
     Preferably, the data are compressed by MPEG compression, and more preferably, by MPEG Layer-3 compression. 
     Preferably, the data are compressed at least 4-fold, more preferably at least 8-fold, and most preferably approximately 12-fold. 
     Preferably, the chip includes firmware for decompressing the data. 
     Preferably, the chip includes a custom integrated circuit chip and does not include a general purpose processor. 
     Preferably, the CD player includes a mobile personal audio player, which is preferably installed in a vehicle. 
     There is further provided, in accordance with a preferred embodiment of the present invention, a CD recording system, including: 
     a read drive, which receives and reads a first CD having audio data recorded thereon; 
     compression circuitry, which receives and compresses the audio data from the read drive; and 
     a write drive, which receives the compressed data and records the compressed data on a second, recordable CD. 
     Preferably, the circuitry compresses the data by MPEG compression, and more preferably, by MPEG Layer-3 compression. Preferably the circuitry includes firmware for compressing the data. 
     Preferably the circuitry compresses the data at least 4-fold, more preferably at least 8-fold, and most preferably approximately 12-fold. 
     There is further provided, in accordance with a preferred embodiment of the present invention, a method for playing a long-playing audio CD, including: 
     reading compressed digital audio data from the CD; and 
     decompressing the data using a custom integrated circuit chip; and 
     converting the decompressed data to analog form. 
     Preferably, decompressing the data includes decompressing by MPEG decoding, and more preferably by MPEG Layer-3 decoding. 
     Preferably, decompressing the data includes decompressing by at least 4-fold, more preferably by at least 8-fold, and most preferably by approximately 12-fold. 
     Preferably reading the compressed data includes playing the CD in a mobile personal audio player, preferably in a CD player installed in a vehicle. 
     There is further provided, in accordance with a preferred embodiment of the present invention, a method for producing a long-playing audio CD, including: 
     reading digital audio data from a prerecorded CD; 
     compressing the data using MPEG compression; and 
     recording the compressed data on the long-playing CD. 
     Preferably compressing the data includes compressing by MPEG Layer-3 compression. 
     Preferably compressing the data includes compressing by at least 4-fold, more preferably, by at least 8-fold, and most preferably, by approximately 12-fold. 
     Preferably, reading the data includes reading data from a plurality of prerecorded CDs. 
     Furthermore, reading the data preferably includes inserting each of the plurality of CDs in sequence into a read drive, in order to read data therefrom. 
     Preferably, recording the data includes recording data on the long-playing CD in an order that is different from the order of the data on the prerecorded CD. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: 
     FIG. 1A is a simplified pictorial illustration of a CD drive, in accordance with a preferred embodiment of the present invention; 
     FIG. 1B is a schematic block diagram illustrating the operation of the drive of FIG. 1A; 
     FIG. 2A is a simplified pictorial illustration of a CD recording system with dual CD drives, in accordance with another preferred embodiment of the present invention; and 
     FIG. 2B is a schematic block diagram illustrating the operation of the system of FIG.  2 A. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIGS. 1A and 1B, which schematically illustrate a CD player  20 , in accordance with a preferred embodiment of the present invention. FIG. 1A is simplified pictorial illustration, and FIG. 1B is a schematic block diagram of the CD player. 
     A long-playing CD  24 , on which compressed digital audio signals are encoded, preferably using MPEG Layer-3 compression, is inserted into a CD drive  22  in MPEG-enabled CD player  20 . An optical read head  26  reads the compressed data on CD  24 , and transfers the data to an MPEG decoder chip  28 . Chip  28  reads the data, and via algorithms known in the art, decodes the compressed MPEG digital data. The uncompressed data is then transferred from chip  28  to a D/A converter  30 . Converter  30  converts the digital data to analog data, as is known in the art, and passes the analog data, which are directly reproducible as audio signals, to speaker  32  or to another output device or output socket (such as headphones or amplifier—not shown). 
     It is noted that the scan pattern and/or scan speed to read head  26  over the surface of CD  24  may be adjusted to accommodate the high density of information on the CD. Also, buffer memories may be introduced between read head  26  and chip  28  and/or between chip  28  and D/A converter  30 , in order to ensure a smooth, properly times stream of audio data from CD  24  to speaker  32 . 
     CD player  20  may be located either in a home audio entertainment center, a portable CD player, a car CD player or any other form of personal CD player, thus enabling a user to hear up to 888 minutes of high-quality stereo listening entertainment from a conventionally sized CD instead of the conventional 74 minutes. Additionally, CD player  20  may also be equipped to play conventional short-play CDs if desired. For this purpose, chip  28  is preferably capable of identifying whether the data read by head  26  is encoded or not; if not, no decoding will take place, and direct digital-to-analog playback will occur. 
     Chip  28  is preferably a custom VLSI chip, incorporating a suitable processor and firmware, stored on the chip, for decoding compressed MPEG digital audio data, including Layer-3 encoded data. Methods of real-time decoding MPEG Layer-3 digital audio data are known in the art. For example, a suitable MPEG decoding software program, known as AMP (Audio MPEG Player), version 0.7.5, which runs on a Pentium-type processor in a personal computer, is incorporated hereinbelow as Appendix A. It is within the capabilities of semiconductor manufacturers to design and produce chip  28  so as to implement the program listed in Appendex A or another, similar program. It will be understood, however, that the functions of chip  28  in CD player  20  could also be performed using one or more chips of other types, for example, one or more ASIC chips and/or a general-purpose processor together with requisite peripheral and/or memory components. 
     FIGS. 2A and 2B schematically illustrate a CD recording system  40 , useful particularly for producing long-playing disks to be played in player  20 , in accordance with a preferred embodiment of the present invention. FIG. 2A is simplified pictorial illustration of system  40 , and FIG. 2B is a schematic block diagram illustrating the operation of the system shown in FIG.  2 A. 
     Recording system  40  comprises a CD read drive  42  and a CD write drive  44 . A conventional CD  50 , containing uncompressed audio data, is inserted into drive  42 , and a blank, recordable CD  52  is inserted into drive  44 . Digital audio data from CD  50  is read by optical read head  26 , which transfers the data to compression circuitry  46 . Circuitry  46  compresses the digital data, preferably using MPEG Layer-3 encoding, as is known in the art. Circuitry  46  may comprise a custom VLSI or ASIC chip or, alternatively or additionally, a general-purpose processor with suitable software, as well as requisite memory components and/or peripheral devices. Compressed data is transferred from circuitry  46  to a write head  54  in drive  44 , which records the data onto CD  52 . 
     Preferably, a user of system  40  chooses one or more tracks of CD  50  to be read, compressed and written onto CD  52  in any desired order. Thereafter, CD  50  is removed and replaced with another CD, from which audio data is read. This operation may be repeated numerous times, thus allowing recording of approximately 888 minutes (14.8 hours) of high-quality stereo audio sound onto one recordable, long-playing CD  52 , based on the 12-fold compression that can be achieved using MPEG Layer-3. CD  52  can then be played in a portable CD player, such as player  20  shown in FIGS. 1A and 1B, thereby replacing numerous cumbersome conventional (74 minute) short-playing CDs with one 888 minute long-playing CD, and enabling the user the freedom of extended listening with one CD. 
     In an alternative preferred embodiment, circuitry  46  also includes decoder chip  28 , or other decompression circuitry, and thus performs both the function of compression to MPEG standard encoding and decompression from MPEG standard encoding, thus enabling recording system  40  to function also as a playback device for long-play 888 minute CDs, similar to long-play CD player  20 . 
     In still another alternative embodiment, not shown in the figures, system  40  may comprise only a single read/write CD drive, along with a fixed mass-memory device, such as a magnetic hard disk. In this case, conventional CDs  50  are first inserted one by one into the drive. The audio data are read from the CDs, compressed by circuitry  46 , then temporarily stored in the mass-memory device. Then recordable CD  52  is inserted into the same read/write CD drive, and the stored, compressed data from the mass-memory device are recorded on the recordable CD. 
     It will be appreciated that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims. 
     SOFTWARE APPENDIX 
     The computer software listing attached hereto comprises source code files for AMP (Audio MPEG Player), written in the C programming language. This code, which is available for download via the Internet at ftp://ftp.rasip.fer.hr/pub/mpeg, may be compiled using any suitable C-language compiler and run on any of a variety of operating platforms, for example, under the Microsoft Windows 95 operating system on a personal computer that is equipped with an Intel Pentium MMX processor. The code is covered by copyright and may be used commercially only subject to the agreement of the copyright holder.