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Shannon, Beethoven, and the Compact Disc See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/322951358 Shannon, Beethoven, and the Compact Disc Article · December 2007 CITATIONS READS 2 1,916 1 author: Kees Schouhamer Immink Turing Machines Inc 267 PUBLICATIONS 2,795 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: rll codes View project recording systems View project All content following this page was uploaded by Kees Schouhamer Immink on 06 April 2019. The user has requested enhancement of the downloaded file. itNL1207.qxd 11/15/07 9:48 AM Page 42 42 recovery of a file possible from reception of data from uncoordinat- [3] ——, “LT codes,” in Proc. 43rd Annual IEEE Symposium on ed senders. Each sender has access to the same piece of data, and Foundations of Computer Science, 2002. creates an independent fountain for this piece. The receivers then combine data received from each of the senders. Because the output [4] A. Shokrollahi, S. Lassen, and M. Luby, “Multi-stage code gen- symbols have been generated independently at each of the senders, erator and decoder for communication systems,” June 27, 2006, from the point of view of the receiver the data received may as well U.S. Patent No. 7,068,729. have been generated by one fountain, at the cumulative rate of all the fountains. Since this way of receiving data is robust against par- [5] A. Shokrollahi, “Raptor Codes,” IEEE Transactions on tial or total failure of the senders, this is the method of choice in Information Theory, no. 6, pp. 2551–2567, June 2006. applications where there is expectation of such failures. [6] J. Byers, M. Luby, M. Mitzenmacher, and A. Rege, “A digital In other applications, such as IPTV and more generally video trans- fountain approach to reliable distribution of bulk data,” in pro- mission over networks, systematic Raptor Codes are used as “tun- ceedings of ACM SIGCOMM ’98, 1998. able fixed rate codes.” This means that only a fixed amount of redun- dancy (or repair data) is generated in a fixed application, this amount [7] 3GPP TS 26.346 V6.1.0, Technical Specification Group Services and may vary depending on the particular network conditions encoun- System Aspects; Multimedia Broadcast/Multicast Service; Protocols tered. Each instantiation would correspond to a code of a different and Codecs, June 2005. rate, but all these codes are generated the same way using the same Raptor code. This flexibility is a key feature for providing video of [8] M. Luby, M. Mitzenmacher, A. Shokrollahi, and D. Spielman, very good quality on networks with widely varying characteristics. “Efficient erasure correcting codes,” IEEE Transactions on Information Theory, vol. 47, pp. 569–584, 2001. REFERENCES [9] A. Shokrollahi, S. Lassen, and R. Karp, “Systems and process- [1] P. Elias, “Coding for two noisy channels,” in Information es for decoding chain reaction codes through inactivation,” 2005, Theory, Third London Symposium, 1955, pp. 61–76. U.S. Patent number 6,856,263. [2] M. Luby, “Information additive code generator and decoder [10] Shokrollahi, A., and Luby, M., “Systematic Encoding and for communication systems,” October 23 2001, U.S. Patent No. Decoding of Chain Reaction Codes,” U.S. Patent 6 909 383, June 6,307,487. 21, 2005. Shannon, Beethoven, and the Compact Disc Kees A. Schouhamer Immink About the author: of music requires about 1.5 million Dr. Kees A. Schouhamer Immink worked from 1968 till 1998 at bits, which are represented as tiny Philips Research Labs, Eindhoven. In 1998, he founded Turing pits and lands ranging from 0.9 to Machines Inc, where he currently serves as its CEO and president. 3.3 micrometers in length. More Kees A. Schouhamer Immink Since 1994, he has been an adjunct professor at the Institute for than 19 billion channel bits are with Claude Shannon. Experimental Mathematics, Essen-Duisburg University, Germany, recorded as a spiral track of alternating pits and lands over a distance of and a visiting professor at the Data Storage Institute in Singapore. 5.38 kilometers (3.34 miles), which are scanned at walking speed, 4.27 The photo shows the author (left) with Claude Shannon during km per hour. the awards dinner at the Convention of the Audio Engineering Society (AES) in New York, October 1985, where Shannon This year it is 25 years ago that Philips and Sony introduced the CD. In received the AES Gold Medal ‘For contributions that made digital this jubilee article I will discuss the various crucial technical decisions audio possible’. made that would determine the technical success or failure of the new medium. Abstract – An audio compact disc (CD) holds up to 74 minutes, 33 sec- onds of sound, just enough for a complete mono recording of Ludwig von Shaking the tree Beethoven's Ninth Symphony (‘Alle Menschen werden Brüder’) at probably the slowest pace it has ever been played, during the Bayreuther In 1973, I started my work on servo systems and electronics for Festspiele in 1951 and conducted by Wilhelm Furtwängler. Each second the videodisc in the Optics group of Philips Research in IEEE Information Theory Society Newsletter December 2007 itNL1207.qxd 11/15/07 9:48 AM Page 43 43 Eindhoven. The videodisc is a 30 cm diameter optical disc that Item Philips Sony can store up to 60 minutes of analog FM-modulated video and Sampling rate (kHz) 44.0 - 44.5 44.1 sound. It is like a DVD, but much larger, heavier, and less reli- Quantization 14 bit 16 bit able. The launch of the videodisc in 1975 was a technical success, Playing time (min) 60 60 but a monumental marketing failure since the consumers Diameter (mm) 115 100 showed absolutely no interest at all. After two years, Philips EC Code t.b.d. t.b.d. decided to throw in the towel, and they withdrew the product Channel Code M3 t.b.d. from the market. t.b.d. = to be discussed While my colleagues and I were working on the videodisc, two Philips engineers were asked to develop an audio-only disc As can be seen from the list, a lot of work had to be done as the based on optical videodisc technology. The two engineers were partners agreed only on one item, namely the one-hour playing recruited from the audio department, since my research direc- time. The other target parameters, sampling rate, quantization, tor believed a sound-only disc was a trivial matter given a and notably disc diameter look very similar, but were worlds video and sound videodisc, and he refused to waste costly apart. researcher’s time. In retrospect, given the long forgotten videodisc and the CD’s great success, this seems a remarkable Shannon-Nyquist sampling theorem decision. The Shannon-Nyquist sampling theorem dictates that in order to The audio engineers started by experimenting with an analog achieve lossless sampling, the signal should be sampled with a approach using wide-band frequency modulation as in FM radio. frequency at least twice the signal’s bandwidth. So for a band- Their experiments revealed that the analog solution was scarcely width of 20 kHz a sampling frequency of at least 40 kHz is more immune to dirt and scratches than a conventional analog LP. required. A large number of people, especially young people, are Three years later they decided to look for a digital solution. In perfectly capable of hearing sounds at frequencies well above 20 1976, Philips demonstrated the first prototypes of a digital disc kHz. That is, in theory, all we can say. In 1978, each and every using laser videodisc technology. A year later, Sony completed a piece of digital audio equipment used its own ‘well-chosen’ sam- prototype with a 30 cm diameter disc, the same as the videodisc, pling frequency ranging from 32 to 50 kHz. Modern digital audio and 60 minutes playing time [2]. equipment accepts many different sampling rates, but the CD task force opted for only one frequency, namely 44.1 kHz. This The Sony/Philips alliance sampling frequency was chosen mainly for logistics reasons as will be discussed later, once we have explained the state-of-the-art In October 1979, a crucial high-level decision was made to join of digital audio recording in 1979. forces in the development of a world audio disc standard. Philips and Sony, although competitors in many areas, shared Towards the end of the 1970s, ‘PCM adapters’ were developed in a long history of cooperation, for instance in the joint estab- Japan, which used ordinary analog video tape recorders as a lishment of the compact cassette standard in the 1960's. In mar- means of storing digital audio data, since these were the only keting the final products, however, both firms would compete widely available recording devices with sufficient bandwidth. against each other again. Philips brought its expertise and the The best commonly-available video recording format at the time huge videodisc patent portfolio to the alliance, and Sony con- was the 3/4" U-Matic. tributed its expertise in digital audio technology. In addition, both firms had a significant presence in the music industry via The presence of the PCM video-based adaptors explains the CBS/Sony, a joint venture between CBS Inc. and Sony Japan choice of sampling frequency for the CD, as the number of video Records Inc. dating from the late 1960s, and Polygram, a 50% lines, frame rate, and bits per line end up dictating the sampling subsidiary of Philips [4]. Within a few weeks, a joint task force frequency one can achieve for storing stereo audio.
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