The high point of interest in this latest player from Philips, not sur prisingly, is its reliance on their new Bitstream decoding system. The CD840 costs a modestly above average £349 but I must hasten to say that you are not paying more for the novel Bitstream circuitry, compared with Philips other current—by now almost traditional-16-bit four-times oversampling decoders. Indeed I am told that the basic simplicity of the Bitstream chips will actually bring prices down. No, the CD840 comes in towards the top of the Philips range primarily because it is absolutely packed with operational features. It can therefore be seen as following a previous flagship model, the CD960 which cost £699 when I reviewed it away back in May 1987 and which I used for many comparison tests in preparing the present review.

The CD840 weighs considerably less than the CD960 (4kg as against 10kg) suggesting a greater use of plastics. However, its unique boxframe construction provides a good measure of rigidity with new shockproof feet, etc. The disc drawer is of the slower acting type, whereas the CD960 is amongst the fastest. All the usual functions are provided, both on the front panel and the fairly elabor ate remote-control handset. These include Random Play, 20-seconds Scan of each track (or 10-seconds if Scan and Fast are pressed together), Repeat, etc. Extra trickery includes not just one but two FTS (Favourite Track Selection) memory stores. FTS began life as an exclusive Philips feature, though I see that others are copying the idea, and has the ability to store the sequence of tracks you have chosen to programme on each of your discs (up to about 200 CDs) and will play that selection automatically whenever the given disc is reloaded into the machine. With two FTS memories ("his and hers" as Philips coyly suggest) you can make up two different programmes for each disc. There is even an FTS Info feature which will display (a) the number of discs programmed in FTS1 and FTS2, (b) the memory space still available, (c) in sequence the number of each disc and the number of times it has been played, (d) the title you have given each disc.

This last Title feature allows you to attach an identification Name or Code of up to 12 characters to favourite selections. These titles appear on a special Active Info strip in the display, as do various other 'helpful' messages such as "Tray Open", "Insert Disc", "Tray Close", "Reading" and "Disc Ready". The brightness of the whole display can be adjusted in eight steps "to suit the room lighting conditions", and there are Personal Presets to introduce separate fade-in and fade-out times, from 0 to 20 seconds, etc. A Record Sync feature which works in conjunction with suitable Philips cassette decks, commands the recorder to start when the CD begins, notes when the tape comes to an.end, returns the CD player to the beginning of the track in play and resumes recording when the cassette has been turned over or autoreversed. It also fits tracks to the given tape length, etc.

As well as the conventional pair of phono sockets for analogue output, for which a twin low-loss cable with gold-plated plugs is supplied, there are both gold-plated coaxial and Toslink optical (lead supplied) digital outlets for feeding to a stand-alone D/A converter or an amplifier having the necessary D/A converter built-in. (Of course these digital outlets bypass the one-bit Bitstream conversion stages.)

The virtues of establishing a worldwide standard specification for any new consumer product were well demonstrated when Philips first introduced the now ubiquitous Compact Cassette away back in 1963. The same potential for compatible interchange of software and hardware in any country in the world were targeted when Philips and Sony drew up the famous Red Book standard for Compact Disc in the early 1980s, to which all licensed disc and player manufacturers must conform. Unfortunately this commonsense recognition of standardization as a prerequisite for proper launching of an ambitious new format has the effect of freezing the performance at the level attainable with current components (chips) and technological know-how. With hindsight, both the musicassette and the CD could have been made even better if their launches had been delayed a few years.

So we are stuck with the 16-bit linear encoding and 44-1kHz sampling frequency standard to which all legitimate CDs are manufactured. However, much can be done to enhance the reliability, accuracy and subjective sound quality provided by this deservedly popular consumer format. The recording, post-production, CD mastering and duplication engineers are continually refining their preparation stages, adopting 20-bit processing for example, to reduce signal limitations on the way to the final (standard) CD pressing. At the same time the designers of up-market CD players have been beavering away at a host of independent circuit and mechanical developments aiming to scan the standard CD more accurately and esponge the audibly degrading characteristics of early D/A converters and analogue output stages. Many of these 'improvements' have contained a large measure of wishful thinking and produced only marginal sound enhancement, even when they have been very complex and unaffordably expensive.

The Philips revolutionary Bitstream approach appeals aesthetically and mathematically to my simple mind. It addresses what I see as the CD format's chief drawback, the quantization error (waveform approximation) inherent in the staircase of possible digital levels provided by the chosen 16-bit encoding. Yet it does so not by going for longer and more expensive 18-bit or 20-bit converters and relying on selected and individually adjusted in situ components to reduce the effective size of the staircase steps. Instead it eliminates the staircase effect completely. I gave a brief explanation of Bitstream when it was first mooted (July 1989 issue, page 252). In outline, the 16-bit digital signal coming from the CD is decoded using a one-bit system, with 256-times oversampling. The II 3 million (44,100 x 256) pulses emerging from the quantizer are given values of + 1 or — 1 and packed more or less densely above and below the zero datum line (Pulse Density Modulation) according to the instantaneous value of the original waveform. Simple analogue low-pass filtering produces the required signal without the usual quantization staircase glitches.

As the table of results shows, the measured performance of the CD840 looks just like that of any other decent CD player, and indeed matches in every particular the older CD960 model. Additional low-level linearity tests now made possible using the dithered tracks on the CBS! test CD confirmed Bitstream's enhanced resolution all the way down to — 90dB. On careful listening, too, subtle differences were detected. The new Bitstream sound was more set back in an apparently warmer acoustic environment. The effect was slight and I can only suppose that Bitstream's claimed finer resolution of low-level signals is allowing us to hear just a little more of the reverberation tail than normal 16-bit converters. There was less masking of inner detail too, producing a nice feeling of characterization from the various instruments and voices.

These differences were much to my taste and in most A/B comparisons I found myself preferring the Bitstream version. There is some loss of brightness and attack, which some listeners may regret (just as some people like to play Dolby-encoded cassettes without the decoding switched on "because they sound brighter"). This does make a centre soloist (Emma Kirkby, for example, in "A feather on the Breath of Heaven", Hyperion (D CDA66039, 7/85) tend to sound not only a little more distant but also marginally softer in tone than through a conventional converter. Which is right? Only a careful comparison with the master tape would give us the answer. For my money (and notice the price reduction from £699 for the old but still splendid CD960 to £349 for the equally versatile CD840) Bitstream has the potential to produce a more musically satisfying sound from well-balanced CDs. I look forward to more machines, including some up-market audiophile models, using this principle. For now the CD840 is an excellent buy and I can strongly recommend it.

(Test Results in brackets)
Frequency response: 2-20,000Hz ± 0-035dB (agreed)
Total harmonic distortion: 0.004% (0-01% including noise)
Signal-to-noise ratio: 100dB (101dB A-weighted)
Linearity: (within 0.5dB down to - 90dB) Channel separation: 100dB (agreed)
Output: 2V fixed (2.IV)
Dimensions (W x H x D): 420 x 90 x 280mm
Weight: 4.0kg
UK retail price: £349.00