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views for hobbyists
25 Years CD: August 17, 1982 - August 17, 2007 and turned 30 in
Or press Ctrl + F and type what you are looking for.
How Does It Work...
The engineers in the world famous Philips Physics Laboratory (NatLab) start working on digital techniques around 1967. A few years later they research the feasibility of the laser video disc combining images and sound. That brings up the idea of making a laser disc just for music and speech with no images added.
The final outcome is a disc of 12 cm in diameter which is read by a laser beam. The disc has a reflective layer, covered by a non reflective layer with holes of various lengths which measure mere micrometers. These holes represent the recorded music. Only when the laser beam is reflected by the disc, the beam is read by a photo cell and the data which it represents are converted into an analog signal.
the resolution of the signal and the depth of the sound are very low in
quality, relative to the analog tape and LP, this disc is to be the modern
successor of the vinyl long playing stereo gramophone record.
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History Starts In 1967
By the end of the nineteen seventies designers of high end amplifiers are concerned about an extreme large bandwidth, they are investigating all sorts of distortions in order to further improve the reproduction. Not just the values of the Total Harmonic Distortion (THD) and how to handle these, but also the newly discovered Transient Intermodulation Distortion (TIM) and Dynamic Intermodulation Distortion (DIM). Digital formats will make all further research for improvements in these fields practically obsolete.
the late nineteen seventies digitally recorded sound is being demonstrated
at the big audio fairs: Funk-Ausstellung (Berlin), CES (Chicago and
Las Vegas), Heathrow (London), Firato (Amsterdam), Festival du Son (Paris),
do fear the arrival of a digital format with such a low resolution.
Especially those who have invested in high end turntables, expensive cartridges,
in tape recorders with professional qualities, in esoteric amplifiers
and grandiose loudspeakers. They have brought the reproduction of the
analog Stereo LP to an extremely high and refined level and are enjoying
pure music, reproduced from records pressed from high grade vinyl with
These are the first lines of an advertisement introducing the CD to the music loving public. The advertisement appears in Dutch newspapers on the 1st of March, 1983.
The first CD is pressed on August 17, 1982, in the Polygram factory in Hannover, Germany.
In Japan the Compact disc is introduced
on November 1, 1982.
Successor to the Stereo LP
Alva Edison is the inventor of the Phonograph
and the vertical engraving of the signal on a cylinder. It is the so called
hill and dale technique which is later used in a disc proposed by Edison
himself and by Pathé in France.
1966 audio journalist Leonard Marcus of High Fidelity Magazine
investigates the future of recording in a very interesting article called
'The Prospects in Audio'. He writes that CBS Laboratories
are developing a new analog disc. It is Dr. Goldmark himself who
demonstrates this new format. It is a 7 inch record with an extremely
fine groove. It turns at 8 RPM and can contain the same amount
of information as a 12" LP. It shows that CBS is a firm believer
in their own invention: the analog long playing record.
that same article in the April 1966 issue of High Fidelity Magazine,
RCA's Dr. Harold Olson tells the readers that the record of the
future will be completely different: ''There will be no music on it, only
a binary code''. He adds that only a very small disc will be necessary.
The way the code will be read is also completely different. No needle
or other mechanical devise will be used. Olson: ''The record could be
read by an electron beam.'' It will be possible to record half an hour
of music on a disc as small as the size of a quarter dollar (according
to Wikipedia the quarter dollar measures 0.955 inches = 24.26 mm in diameter).
the April 1966 issue of High Fidelity, pianist Glenn Gould writes
an essay on
prospects of Recording''. He goes even further and predicts
that the listener will have a console with a keyboard in his listening
room. After typing the title of the work he wishes to hear, say Beethoven's
Emperor Concerto, he can choose from a list of available recordings. After
entering the selected performance, the music signal will be sent by cable
to his hi-fi set and a small sum will be deducted from his bank account.
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Working On The Future
Tape recorder manufacturer AMPEX is experimenting with a digital tape format. IBM is computing with big machines using reel to reel tape recorders and connecting their clever Selectric typewriters for printing the data sheets. However designing a digital tape recorder for sound is a complicated affair. The marketing of such a recorder is impossible as the cost is $150.000 per unit.
Laboratories are concentrating
on the idea of the Vocoder. The Vocoder divides the frequency band in
several sections. Each section is represented by a code (which is a single
frequency, akin to FM and the carriage frequency in Quadro). These codes
can be transmitted via telephone lines, as transmitting speech is the
original idea of the inventor. Naturally these frequency codes can also
be stored on a disc. The transmitted or stored single frequencies can
be translated again to the original sections of the audio band which,
together, form the complete, original audio spectrum. The inventor of
this method is Homer Dudley. He devises this system in 1928! Now
Bell assesses if a further development for recording purposes is possible.
Telefunken: 'Vinyl' Video Disc
In Germany, in 1965, Telefunken starts working on the development of a new carrier which is much larger than Dr. Olson's quarter dollar. Telefunken's laboratory system consists of a 12 inch disc. It contains digitally encoded signals for video and audio. It is a floppy disc made of thin PVC. The information is written in a vertical script with varying depth, akin to Thomas Alva Edison's hill-and-dale, so to speak. The variations are mere micrometers. The disc turns at 1500 RPM. That is 25 turns per second. Each turn represents a video image. In order to have equal density for every turn, only a small area of the disc can be used. The total playing time of an entire disc is 12 minutes. If the disc can contain images and sound, it sure will be possible to make a similar disc with sound only.
the Telefunken system the information can not be written at the high playback
speed, so it will have to be "recorded" at a tenth of that speed
and takes 2 hours to be completed. The disc rests on an air cushion. The
differences in pressure are sensed by a piezoelectric pick up system which
moves in a tangential arm. The diamond prism ensures the correct distance
between pick up and record. The down force is 0.2 gr. The use of a carrier
wave of 6 MHz is possible. This proposition is a rather primitive
one. It still reminds one of the vinyl gramophone record. This mechanical
method with the usure of disc and diamond (enabling 1000 playings), is
certainly not the way.
Philips Video Disc: LaserVision.
Philips Video Disc: LaserVision
1967 the engineers of the famous Philips Natuurkundig Laboratorium
(Philips Physics Research Laboratory - Natlab) start researching the
development of a video disc. It is an optical system instead of a mechanical
one. Around 1980 the system will be ready for introduction and is named
LaserVision. In 1967 the engineers realize, that, when omitting the images,
they may have the possible successor to the LP, the long playing record.
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The 1970s: Developing The Standard
Japan Broadcasting Corporation
1969 the Technical Research Laboratory of the Japan Broadcasting Corp.
demonstrated their digital system known as Pulse Code Modulation which
was looked at with great interest by large electronic companies in Europe
and the USA Billboard reported: "Nippon Columbia (Denon, Ed.) earned
the cooperation of the laboratory and (...) came up with a PCM recording
system which opened the door to noiseless and distortion-free recording."
Sophisticated Recording Equipment
produced PCM recordings as early as 1973 of artists like pianist Takahiro
Sonoda, pianist Yuji Takahashi, harpsichordist Zuzana Ruzickova, pianist
Annerose Schmidt, pianist Deszo Ranki, pianist Zoltan Kocsis, etc. The
recordings of Mozart's Complete Piano Sonatas by Maria João Pires
won several awards.
of Denon's PCM recording system:
Telarc claims on their web site: "Even before the public had heard of the digital process, they were embracing the sound of Telarc." This is of course not correct. Telarc was founded in 1977, while from 1973 on Denon released their vinyl Digital PCM Discs.
Denon (Nippon Columbia)
the end of 1974 the world wide adopted digital format is the 44.1 kHz/14
bit PCM format. PCM stands for Pulse Code Modulation. The sound
is measured at specific intervals by a pulse. A higher sampling frequency
than 44.1 kHz. and a higher quantization than 14, are not yet feasible.
A gradually growing catalog is offered to the record buying public with popular music, jazz, folk, and classical music. The classical recordings feature flute player Jean-Pierre Rampal, the Josef Suk Trio, the Tokyo Metropolitan Symphony Orchestra conducted by Louis de Froment, the NHK Symphony under Otmar Suitner, the Berlin Philharmonic conducted by Kurt Sanderling; pianists Maria Joao Pirez, Anne Rose Schmidt, Vlado Perlemuter, Deszö Ranki; cellist Janos Starker; violinist Josef Suk; organist Helmuth Rilling. From 1982 on many of these recordings are made available on Compact Disc also.
The A & R Department
people of the Artist and Repertoire Department of the Denon PCM label
(Nippon Columbia) knew well their way around and with taste. One of the
many fine recordings was the performance of Mussorgsky's Pictures from
an Exhibition played by the Tokyo Metropolitan Symphony Orchestra conducted
by Louis Fremaux (X-7072).
Denon's PCM LPs Reassessed
left you see the cover of LP ST-6007 from 1979. It contains excerpts of
the Denon catalog of PCM recordings. This promotional release and other
records from the nineteen seventies show all to clear the quality of the
recordings made before the advent of the Compact Disc.
Japan Victor Company - JVC
Another developper is JVC, the company known for their consumer products and the CD-4 Discrete 4 Channel Quadraphonic sound recording system. In 1980 JVC's digital format has the standard 14 bits and sampling frequency of 44,056 kHz. At left the cover of The Devil's Trill, a Varèse-Sarabande LP featuring violinist Vlaclav Hudecek and pianist Josef Hala who have been recorded using the JVC VP-1000 Digital recording system.
Miller & Kreisel and Sony
the beginning of digital recording Sony U-Matic recorders in conjunction
with separate converter modules are being used. Sony develops the PCM
1600 Digital Studio Recorder which becomes very popular. When the 1600
becomes available, more labels start recording digitally. Miller &
Kreisel is such a label. The recordings are made with a Sony PCM 1600
with a sampling rate of 44.1 kHz. and the dynamic gradation of 16 bits.
Jonas Miller and Ken Kreisel design their own electronics and modify
the microphones. Their objective is to achieve a recording with the least
phase shift and name it M&K RealTime Recording Process.
Sony soon replaced the 1600 by their PCM-1610 Digital Audio Processor,
a recording tool that - if used intelligently - can outperform many a
modern low bit processors.
Soundstream, Telarc, Digitech, a.o.
The producers and recording engineers of Telarc, and Digitech use a different digital format. It is devised by Soundstream and has a sampling frequency of 50 kHz. which results in a slightly wider frequency band of theoretically up to 25.000 Hz. before the phase (time coherent) destroying brickwall filter comes into action. But what is a high resolution PCM recording format? The format of the Compact Disc with its 16 bit and 44.1 kHz. or the 48 kHz. of the digital audio recorder (DAT) can hardly be called high resolution formats, nor can the Soundstream digital technique. They only get a widfer frequency band and a higher resolution when two converters are used by Pioneer in their Wide Range DAT.
for the Soundstream Digital Recording System:
Data taken from Digitech DIGI 103 with Anthony Newman on the Historic Hilborne Roosevelt Organ (Great Barrington, Massachusetts.)
Right from the beginning of the digital era the Delos label released the recordings with clear and crisp string sound of the Sequoia String Quartet made when using the Soundstream digital recording system. These performances were masterfully cut and pressed on perfect vinyl. At left the cover of D/DMS 3004 cut in the groove by famous Stan Ricker who was the chief engineer for this recording which was produced by Amelia S. Haygood. Stan Ricker used a transformerless cutting system of JVC and he used Pyral lacquers which were still available in 1979 when these sides were cut.
For most recordings CBS used the Sony PCM 1600 converter/video adaptor which was connected to a Sony U-matic video recorder. When the 1610 was available, the sound engineers used that device. Many recordings were mixed and mastered on the CBS DisComputer. There are also a few CBS recordings done using the Soundstream System. The performances of Beethoven's Cello Sonatas Nos. 1 & 2 by Yo-Yo Ma and Emanuel Ax were recorded with the Sony PCM 1600 (CBS D 37251). For their recording of Sonatas Nos. 3 and 5, the Soundstream system was used (CBS IM 39024). And for Sonata No. 4 and Seven Variations WoO, Sony's PCM 1610 was the converter/video adaptor.
Mixing to Two Channels on the Spot
The new digital format confronted any producer and any sound engineer with quite a few difficultes. Apart from the limitations of the digital format, the biggest problem was that multitrack recorders - if available - were very expensive. So the sound picked up by the various microphones had to be balanced on the spot, and the signals had to be mixed down then and there to the two channels of a stereo recording. These signals were then converted by a Sony PCM-F1, or a PCM 1630, and recorded on a U-matic or even a Betamax video recorder. No re-mixing at a later date was possible. That is what "direct to digital" in most cases meant.
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The Industry: Agreements and Demonstrations
Sharp's prototype of a digital audio disc with 16 bit quantization and 44.1 kHz. sampling rate, stored on a 13.5 cm disc.
Pioneer and Sharp
1980 a committee discusses the standard of a future digital disc once
again. Pioneer proposes a digital audio disc with a diameter of 13.5
cm instead of 30 cm (12"). The sampling frequency shall be between
44.1 kHz and 50.4 kHz. It will be a linear format with 16 bit. The
maximum playing time will be 60 minutes. The disc shall be playable in
their Laser Video Players made for 12" video discs as well.
development of the Philips Laser Video Disc (LaserVision) and its player
led to the creation of the CD-Video Disc and Player (introduced in 1987)
thus paving the way for the DVD.
the format Philips is working on is a linear format and not on a logarithmic
format. It means that the number of samples vary with the frequency.
The higher the frequency the fewer the samples. It also means that
the width of the frequency band for audio depends on the chosen sampling
and Transient Response
higher sampling frequency will result in a wider audio band. The later
adopted 48 kHz. for the Digital Audio Tape Recorder (DAT) means an audio
band extending to 24.000 Hz. A sampling frequency of 400.000 Hz. would
mean an audio bandwidth from DC to 200.000 Hz. and practically no phase
shift, and a fast risetime which is in fact hampered by the 20 kHz of
the CD format. A large bandwidth is necessary to produce a true to live
That is the time when computer freaks are working with a Sinclair, a Commodore, an Atari, with 8 bit and a CPU with 4.43 MHz., storing data on a cassette tape with time consuming writing and reading.
word gets around that Philips will propose a digital disc with the 14
bit/44.1 kHz format, editor/publisher Peter Aczel inspires the readers
of The Audio Critic to send postcards to Philips in Eindhoven,
the Netherlands, to urge the engineers to choose a sampling frequency
of at least 50 kHz.
Development together with Sony
After consultations with Matsushita (Technics) and Sony, it is Sony who joins Philips to finalize the development of the Compact Disc. Philips has a 60% interest and Sony 40% in the joined venture. Apparently Philips is mainly responsible for the laser technology and Sony for the correction codes. You all have heard the story that Herbert von Karajan was happy that the capacity of the CD could contain the complete recording of Beethoven's Ninth Symphony. All physical and digital specifications and data are contained in The Red Book. But you only need ears to be able to judge the benefits and the less positive aspects of the medium.
Prototype of the CD. Like the LP it has a paper label and the cover is a sleeve of thin card board. The jewel case has yet to be designed.
Festival du Son in Paris
the Spring of 1981, well before the official introduction of the CD, Philips
demonstrates their newly developed Digital Compact Disc at 'Le Festival
du Son' in Paris. People are elbowing their way into the small auditorium
to witness this historic event. When a Philips engineer needs to check
the equipment and lifts part of a long and wide, gray curtain, it is immediately
clear that Philips uses stacks of electronics: amplifiers and cabinets
filled with digital circuitry for converting and correcting the signal.
The interconnecting cables are thick and heavy. It shows all too well
that at that time the elaborate circuits and complicated modules for conversion
and correcting any mistake made while reading the disc, has not yet been
reduced to a few ICs, chips and a couple of operational amplifiers. The
cabinets filled with components recall pictures of a demonstration at
a World Fair in the early years of the past century. There is something
primitive about it. But there is also the thrill of witnessing the beginning
of a new era: sound recording and reproduction by means of a computer.
The development of tiny converters and operational amplifiers is certainly
on its way. But no risk shall be taken during such an important demonstration.
Yet it will not take long before electronic circuits and converters are
reduced to the size of a mere IC.
Armstrong and Mussorgsky
do remember the demonstration of Louis Armstrong's digitally remastered
trumpet, sounding round without a chiseled top. Also an original digital
Philips recording of Mussorgsky's "Pictures at an Exhibition"
performed by the Concertgebouw Orchestra, conducted by Sir Colin Davis,
can be heard. The introductory trumpet sounds indeed unstable, is shifting
in intensity from bit to bit, as it is recorded at a low level. Apparently
no dither is added as it is not yet en
vogue. The recording is also issued as LP with reference
number 9500 744 and a few years later as CD 411-473-2. When listening
to this recording in whatever format, it is clear that the recording technician
is still "thinking analog".
doubt, the creation of the Compact Disc is a technical feat of the highest
The digital recording made by Philips of Pictures at an Exhibition as performed by the Royal Concertgebouw Orchestra conducted by Sir Colin Davis transferred to LP 9500 744 and later available on CD 411-473-2. At left the Denon PCM recording with Louis Fremaux and the Tokyo Metropolitan Symphony Orchestra (OX-7072-ND) from 1972. The different approaches by the respective producers and recording engineers are clearly audible.
But that is looking at the medium from a technical point of view, that is looking from the point of view of the proud engineers of the Philips Research Laboratory, the point of view of the Sony engineers, the point of view of the marketing people and the record companies who - first reluctant - finally will accept the new world standard, a format with a channel bit rate of 4.3218 Mb/sec and a data bit rate: 2.0338 Mb/sec. Yes, there is no dust in the groove, there is the absence of the sound of the stylus in the groove, there are no scratches, there are no dents, no pressing bubbles. But there is the lack of resolution, and there are the anomalies (differencies) in the clock frequencies of player and DAC, the importance of which are gradually being discovered by engineers and designers. Serious music listeners who knows how acoustic instruments do sound, hear these technical aspects without knowing the technicallities by name or effect. They are judging the new medium with cautious ears. It is said that the late Jaap van Ginneken (long time producer at Philips' Phonografische Industrie - PPI, later to be named Phonogram and Polygram Records) did express his doubts, if not to say that he was against this limited format.`
Apples to Oranges
In the early days of CD, one journalist noticed that there were readers of his magazine who did not like the CD. He compared the attitude to that of the music listeners in the early years of the LP. They did not like the dull sound of the (early) LP if compared to that of the 78 RPM direct to disc recording. That journalist made of course a mistake. The change from 78 RPM to LP cannot be compared to the introduction of the CD. Both shellac and vinyl in the nineteen fifties had high resolution analog sound, restricted by the bandwidth of the respective carriers. And that is completely different from digital encoding and the problems it poses. It is not only the resolution but also the phase which is incorrect because of the CD's restricted bandwidth.
However, it is the convenience which leads to the general acceptance of the CD format and this prevents the inventors to develop another PCM format with a much higher sampling frequency, higher quantization and consequently a higher bit rate. There is no alternative!
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16 bit and 44.1 kHz.
chief determining factor of the linear recording system is the sampling
frequency. In case of the CD it is 44.1 kHz.
Hz. Sampling Frequency
in the early nineteen eighties I remember fantasizing with John Watson
(of Mission Electronics at the time) about a very high sampling frequency
of say 700.000 Hz. well knowing that this will result in a high resolution
sound recording. Or take the sampling frequency of 400.000 Hz. as is the
argument of designer Tim de Paravicini in the nineteen nineties. That
frequency will give an audio band extending to 200.000 Hz. This means
that the number of samples at 20.000 Hz. is 8. And this brings about the
resolution of a professional reel to reel tape recorder. Furthermore a
6 dB filter - which is phase coherent - can easily be applied at 20.000
Hz. To some the 200.000 Hz. bandwidth may seem rather far fetched. In
the analog days a basic bandwidth of 400.000 Hz. for sophisticated phono
stages was not at all uncommon.
The format of the linear CD has a theoretical bandwidth of 1 Hz. to 44.1 kHz. In practice however the audio band of 1 to 22.050 Hz. can only be used. The frequency band from 22.050 Hz. to 44.1 kHz. cannot be used. It is the mirror of the 1 H - 22.050 Hz. band. In other words it is the alias. Not a bit of the 22.05 to 44.1 kHz. band shall interfere with the music. In order to prevent a mix up, the insertion of a steep filtering by means of a so called brick wall filter, is applied. In theory the slope of that filter should be 96 dB. That is a very difficult value to implement with an analog filter. That is why sometime later the filtering will take place in the digital domain. This makes it possible to insert a less steep filter in the analog domain.
number of samples in the audio band is frequency dependent. The lowest
frequencies are being measured many times more than the top frequencies.
The frequencies from about 11.000 Hz. to 20.000 Hz. are sampled only 2
Linear Format and Oversampling
The computer of the PCM recorder has a steep filter otherwise recording was not possible. The same goes for the CD Player. There is however a way to avoid such a filter with a very steep slope. The Philips engineers introduce the so called oversampling. This is a very clever technique. By multiplying the sampling frequency by 4, the sampling frequency will be seen as 176.4 kHz. instead of 44.1 kHz. and an audio bandwidth of 88.2 kHz. is suggested. This also means that the aliasing is far away from the music signal, the actual audio band of 10-20.000 Hz. Yes, 176.4 kHz. would be quite an ideal sampling frequency. Such a high frequency does not need a steep filter. This multiplication has the benefit of "interpolation". Steps between one level (bit) and the next level (bit) are being generated. This results in a more analog like sound wave.
6 dB per dynamic step does not promote refinement.
This is also true for recordings of orchestral music. In the beginning the recording equipment was not as sophisticated as it is today. In order to give the sound of the recording of Symphony No. 4 of Anton Bruckner with Bernard Haitink conducting the Vienna Philharmonic Orchestra more depth and concert hall atmosphere, recording engineer Volker Strauss took the ready tape to a little church in a small village in the Veluwe region (the Netherlands), played the music and added a well chosen amount of the natural reverberation of that church to the final tape from which the master was etched for the CDs to be released. It was a sort of acoustic feedback so to speak. Without this measure the music would have sounded less agreeable, would have less depth, would have a dry characteristic. Volker Strauss said so when interviewed for Dutch opinion weekly "Vrij Nederland".
Because there are 16 bits, the difference between silence and loudest music (the dynamic range) is 96 dB. The quantization of 16 is a rather low number. At the time of the development of the Compact Disc a higher number of bits was not feasible. Today 64 bit can easily be applied when designing a format. But in 1980 16 bit is the maximum and already superior to the 12 bit/32 kHz. which is then used in broadcasting transmissions. And it is very superior to the 4 or 8 bit of a simple computer. The higher the quantization, the more depth the sound has. (Note: This adagio is also true for images made with a digital camera and with a scanner.)
can make a recording at 20 bits, 24 bits and even 32 bits and storing
them on a digital tape recorder or a hard disk, if you have the appropriate
converters (preferably of the multibit design). Or make an analog recording
with 700 "bit" (so to speak, or gradations) if we don't count with the
fact that a bit is 6 dB and not 1 dBb.
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High Resolution Sigma Delta
is another way of devising a digital format. It is a system by which every
frequency is measured with the same sample rate. It is, like the analog
recording technique, a logarithmic sound recording format. That is what
originally is called the sigma-delta method. The name is later used for
high quality linear converters.
All drawings Copyright by Rudolf A. Bruil
Delta: Natural Harmonics
As the number of samples is the same over the entire audio band, there is the same resolution and depth at every dynamic level: the same high resolution with every bit. While the linear digital formats suffer from inaccuracy at low recording levels, the resolution of the nonlinear (delta sigma) format is the same at all dynamic levels, loud passages or soft music. The harmonics are therefor very natural and logic. (Note: Digital photography suffers from the increasing inaccuracy at each lower level as the linear digital audio formats do.) Needless to say that the sigma delta asks for extremely clever calculations and corrections in order to have an impeccable, linear audio band in the end. In 1980 - let alone in 1967 - such a complex method is only a theoretical option and if put into practice, it would need a completely different sound carrier instead of the CD.
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ln the Beginning
the beginning, the CD is not at all the sophisticated medium as we know
it today. In the first years the percentage of rejected CDs with pressing
faults is high. The spiraled track with the small pits has less than
1.6 micro meter room.
in this respect is the precise adjustment of the Most Significant Bit
(MSB). As the bits are 6 dB which is a rather large span, a small irregularity
does impair harmonics.
CD-100 by Philips
CDP-101 by Sony
only high end magazines like Stereophile and The Absolute Sound, a.o.,
also Stereoplay and Audio in Germany, IAR in Canada, HiFi News in Great
Britain, in fact all over the world audio journalists are reviewing
the players and are coming to grips with the benefits and the anomalies
of the new format. They report on every little improvement.
Graf, managing director of
Thorens A.G., publishes a magazine article with the meaningful
title: "CD, A Misperformance" (CD, eine Fehlleistung).
He argues that most people have never heard the high quality reproduction
of the high resolution analog black vinyl disc. He is right of course,
as only 5 to 10% of people have ears and probably have invested in some
sort of quality audio. And the rest? It is true that many a lover of
pop music, often does not care whether the disc is slipped back into
the cover when partying. Some seem to use the LP as a Frisbee. Many
forget about checking the diamond tip at regular intervals, unaware
of the significance of maintenance. For those the CD is a blessing.
However, many fans of classical music and serious collectors of jazz
do care about maintaining the high quality of the LP. Armin Graf certainly
writes the article also because Thorens is afraid to loose their market,
which they eventually do before starting anew.
manufacturers of CD-Players and converters try to improve the reproduction
of digital recorded sound. They incorporate valves in the amplifier
stage: California Audio Labs, Luxman, Sonic Frontiers, Musical Fidelity.
Beard produces the DAP-1 with 3 sampling frequencies, three 16 bit converters
applying 4 times oversampling. Filtering is practically unnecessary.
The DAP-1 works fantastic with the Philips CD-822 unit, illustrating
that not every DA-Converter gives the same performance with every player.
Cambridge Audio places up to four converters in line to eliminate the
brickwall filter (Cambridge Audio).
the nineteen eighties it is Marc Guisto from France, designer of the
remarkable Guiston tube amplifiers and loudspeaker systems, who uses
the capabilities of the RIAA phono stage: a minute signal is presented
to an amplifier stage with a wide frequency band for optimum harmonics
and transient response. He designs his "convertisseur numerique-analogique",
which of course is not a DA-Converter in the strict sense.
listening to old records pressed in the nineteen fifties and sixties,
the hiss and surface noise do suggest a wider frequency band than the
actual recording has. The noise mixes with the sound of the instruments.
This is the principle Pioneer uses in their "Legato Link"
conversion introduced in 1992. They use the noise above 22.05 kHz. which
normally is being filtered out. This noise is of course filtered. The
engineers devise a method of connecting this noise to the audio frequency
band containing the music. If the level is carefully adjusted, the sound
of the cymbal, the cello, the violin, etc. is reproduced with uncanny
naturalness. If the level is too high, the sound is no longer recognized
as being natural. Click on the picture at left to view a larger image.
Denon engineers follow a completely different path. After analyzing
the complex algorithms of the CD they find a way to extract and use
data from the lower, least significant bit, well before the actual conversion
takes place. These data represent pulses of sounds with high dynamics
occurring mostly at the beginning of a sound. These data are processed
in such a way that they are added to the actual converted wave form.
In popular terms, the steep filtering around 20.000 Hz. is disabled
for a few milliseconds every time the data give a specific value. The
disabling can be just once in a while or can occur repeatedly. During
these instances the width of the frequency band is not limited by the
conventional process of conversion and its brick wall filter. No, it
extends beyond 20.000 Hz. In this way upper harmonics can be generated.
The result is that all acoustic instruments do sound more natural, have
an analog quality. The Denon engineers call it "Alpha Processing"
and introduce this conversion type in 1993. In designing their flagship
DP-S1/DA-S1, they also pay the utmost attention to the construction
and functioning of the CD-turntable.
The benefits of Alpha Processing are not only heard, but can also be measured. Look at the four wave forms at the left:
a = An original 1 kHz. sinus wave.
b = The sound is digitally recorded at minus 90 dB and after being treated by a multi bit D/A converter, the sinus is more like a small number of stairs. The level of -90 dB is of course an extreme low recording level, chosen to demonstrate the workings and benefits of Alpha processing.
c = The signal is converted by means of a low bit or single bit D/A converter. The sinus looks like a woolen thread still showing the rudiment of the steps of a staircase. The oversampling of 256 times also multiplies the smallest inaccuracy and distortion 256 times, hence the thicknes of the sinus wave. The multiplied noise is audible in a low bit CD converter and in the SACD (Direct Stream Digital) conversion. This distortion has to be filtered out by means of a noise shaping filter.
d = If the signal in the Pulse Code Modulation used in the Compact Disc format and is retrieved and converted using alpha processing, the sinus is as, or close to, the original.
the introduction of low bit converters, which are cheaper to produce,
there are manufacturers who stick to the precise adjustment of every
bit. They are the adepts of the multi bit conversion and use high quality
Burr Brown converters. To arrive at a very precise and analog like sound,
the engineers of Accuphase take 4 converters for every bit. The result
is that the dynamic steps are more refined. But not only that. The distortion
is decreased by a factor 4 which is important for lower levels where
common DA-Converters show the original high levels of distortion.
Only A Paper Moon
hobbyists take part in the discussion and many a recipe they come up
with to remedy a specific problem, often turns out to be just snake
oil. Or the solutions are valid for the audio set of that individual
only. And many times the differences are just too subtle for one aspect
while neglecting another.
In the early days of the CD most recording technicians and sound balance engineers need to get to grips with the new medium. They discover that the microphone placement used for analog recording is not valid any longer. Instruments and instrument groups need closer miking. Otherwise the less than perfect resolution at low recording levels will be noticed. If the clarinet in Gershwin's "Rhapsody in Blue" is positioned in the back of the orchestra, far away from a microphone, it is possible that the shifting from one dynamic level to another (from one bit to another) can be heard. The addition of dither (a low level of digital noise) brings the sound a few bits higher and it can be recorded more precisely.
more than three microphones (as in Robert C. Fine's Mercury Living Presence
recordings) and position these close to the instruments or groups of
instruments (multi-miking) will easily result in differences in phase
(time) and harmonics can be canceled out. Not only the harmonic build
up of sounds but also the stereo image will suffer. Attributing to each
microphone (or group of microphones) a separate AD-converter which allows
phase correction, is the solution.
Demonstrates PCM at 45 RPM
In order to emphasize their important part in the development of digital audio and the upcoming revolution, Denon releases another demonstration disc in 1980 with on the cover their range of moving coil cartridges. Maybe there was some concern that the CD would decrease sales severely so they had to stop producing them. For some cartridge manufacturers that became a reality. Not for Denon. Their cartridges are still choices for many audiophiles who do not want to drown themselves in the above $5000 category. The disc had several tracks with all kinds of music plus two tracks for channel check and balance check respectively.
German HiFi Institute
In the acceptance of the Compact Disc magazines played an important role. With the large numbers of subscribers they became the most important platform for promoting the new digital audio format. It was engineer Karl Breh, once chief editor of HiFi Stereophonie and a leading figure in the German audio world, who had the idea to ask Albrecht Gasteiner to produce a long playing record with digital recordings. For instruments and ensembles the microphone technique differed. For the piano recording of Beethoven's Piano Sonata No. 23, "Appassionata" (performed by Peter Efler, the MS configuration was used. For the recordings of "Junges Blechbläserensemble Baden-Würtemberg" and the Swiss Chamber Orchestra, Jürg Jecklin was asked to join. These ensembles were recorded using the Jecklin disc microphone (Scheibenmikrofon). The LP was released in 1980.
1986 a recording engineer/producer tells me that the Compact Disc needs
a completely different approach. The already mentioned recording of
Mussorgsky's Pictures with the Concertgebouw Orchestra and Sir Colin
Davis is the audible proof that in the early days of digital, the technicians
are still "thinking analog" which results in a less chiseled
sound character of this (nevertheless) very well recorded performance.
It is more and more recognized that the restricted format of the CD is also a blessing. Now the format is more or less prescribing what the outcome will be: 44.1 kHz. is 44.1 kHz. and 16 bit is 16 bit. The CD-Player incorporated in the playback system is more or less definite. There is no worry about the necessary exchange of the cartridge's needle in the turntable. The CD-Player just performs the same, time after time. That can also be regarded as its drawback. To improve not a needle or a new cartridge has to be bought, but now an entire player or Digital to Anaalog Converter has to be bought.
the converters are being improved upon. And further understanding of
the algorithms result in software which is getting better and better.
And then there is the benefit of breaking the codes for all sorts of
editing purposes. The signal can be copied, pasted, repeated and it
can be changed (cleaned). The re-recording and editing of historical
performances is possible.
The Versatile LP
analog direct-to-disc recordings are the most expensive and the most
ideal when judging on quality of sound alone. The drawback of the vinyl
long playing record is however that only a restricted number of copies
shall be pressed. A number of 1500 per matrix is the maximum if a relatively
high level of quality is to be guaranteed.
restriction of the CD is the chosen sampling frequency which sets the
width of the frequency spectrum of the format. The chosen number of
bits determines the dynamic detail and the depth and harmonic build
up of the sound. The 16 bit and the clock frequency of 7 MHz. of 1982
look rather poor if compared to the 64 bit and 4 Giga Herz. processors
with which modern computers are operating.
LP Record and UDF
The gramophone Long Playing record - despite its physical shortcomings - can again demonstrate its versatility. Sound which is originally recorded in a high resolution digital format can be engraved in the analog disc. No need to manufacture a player for that format, unless the UDF-Players of the future can accept extra boards with the appropriate converters.
At left the covers of The Last Sony-CBS LP pressed in the Netherlands in March of 1998. The factory was sold and is still pressing some 6 million records a year.
The other cover is of digital Philips LP 6570 994 from 1981 including a catalog of the first Philips digital recordings of classical music.
link at left should lead you to a CBS Sunday Morning report of
PHONO on YouTube.
But CBS deleted this instructional clip. We regret this immensely as the report compiled by clever journalist Thalia Assuras was so well done. Recently it surfaced again as a somewhat altered video. CBS Sunday Morning - It's a Turntable.
So it is replaced by the first of a series of videos originating from forwardbound's channel on YouTube explaning: How Vinyl Records Are Made.
If you want scientific proof of the difference between the frequency range of LP and CD you may want to view The VWestlife Experience on YouTube.
Click on the image at left or click on the link bedlow:
you may also visit this page later:
"In the old ages..."
and see how records were pressed in the early 1950s.
Cut your own records? If you are technical and musical and you have a few dimes to spare, you can do that today.
Rudolf A. Bruil.
Page first published on August 17, 2007 and expanded since.
This is the translation and adaptation of an original article,
written in Dutch and published in the Spring of 1993.