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HIFI REVIEW YAMAHXS BRILLIANT COMPACT DISC PLAYER You've heard of 2-times oversampling and 4-times oversampling in CD players. Now there is 8-times oversampling, as featured in Yamaha's top of the range CD player, the CDX-1110. It provides unrivalled linearity and a brilliant signal-to-noise ratio as we found when putting the CDX-1110 through its paces. By LEO SIMPSON When CD players were first introduced five or so years ago, the available 16-bit digital-to-analog converters were pushing the very limits of VLSI (very large scale integration) technology. Linearity was a real problem, especially at signal levels below - 60dB with respect to the maximum output level of 2V RMS. So much so, that one of the biggest players, Philips, elected to use a technique called "oversampling" which enabled them to use 14-bit D-A decoders. Philips claimed (and reviewers confirmed) that this technique gave results as good or better than available 16-bit decoders. Philips also opted to use dual D-A decoders 20 SILICON CHIP and thereby was able to claim an advantage of no phase delay between channels at the higher frequencies. There was a further advantage in that the filtering required to remove the sampling artefacts was less severe. That was then. In the intervening years, many manufacturers have used the oversampling technique to improve on the performance available from 16-bit decoders. Yamaha has used 2-times oversampling at 88.ZkHz while more recently they and some other manufacturers have employed 4-times oversampling, at 176.4kHz. Now Yamaha have leapfrogged all the rest by introducing their 8-bit oversampling machines which run at 352.BkHz. Why so high? We're not going to delve into all the technical background because it would make this article too long but there are three reasons to increase the sampling rate to 352.BkHz. First, improved linearity; second, better signal-tonoise ratio; and third, very low sampling artefacts in the audio output of the player. There are a number of other technical advantages but as far the user is concerned, those listed are the important ones. As spectacular an advance as the jump to 8-times oversampling may seem, that is not the whole story as far as this new CD player from Yamaha is concerned. It also offers 18-bit D-A conversion and digital control of the output level. What's that you say? How can a 16-bit CD player have an 18-bit decoder? We'll come to that later. Presentation The styling and presentation of the latest CD player from Yamaha is very much in the mould of 16-BIT NO OVERSAMPLING / " \ V SIGNAL I DIA \ CONVE RTER OU TPUT I WAVEFORM AFTER DIA CONVERSION '-ERROR WAVEFORM OF ABOVE SIGNAL (DISTORTION) HI-BIT 8 TIMES OVERSAMPLING AT 352 .8 kHz SIGNAL WAVEFORM AFTER DIA CONVERSION DIA CONVERTER OUTPUT ERROR WAVEFORM OF ABOVE SIG NAL Fig.1: these photos and diagrams show the difference between normal 16-bit sampling at 44.lkHz and 8-times oversampling at 352.BkHz. Notice that the steps in the re-constituted audio waveform are much smaller and sampling artefacts to be filtered out are greatly reduced. Manufacturer's Specifications Audio section Frequency response ....... ... .. ....... .... .. 2Hz to 20kHz within ±0.3dB Total harmonic distortion .. .. .......... .. ...................... less than .002% Signal-to-noise ratio ... ... .. ... ...... ... ... ... .... .... ... ............... ..... 118dB Dynamic range ....... ... .... ............ ..... ...... .. .... ...... more than 1 00dB Wow & flutter .. ... ... ......... .... .... .. .... .. .. .. ..... .. ........ .. . unmeasureable Channel separation .... .... ... ...... ..... more than 1 00dB (1 kHz , 20kHz) Maximum output voltage .. .. ... ......... ... .. .. .. .... .... .. .. ... .. .. 2 volts RMS Output impedance ...... ... ... ..... ..... .... .. ....... ........ ... ... ... .... . 4 7 ohms Headphone output .... .. ........ .............................. 3 volts/150 ohms Internal system Optical pick-up .. ..... .......... ......... .... .......... ... ..... .. .... .. 3-beam laser Error correction system ........................ ..... ............ .. .. .. .. .. ... CIRC Digital-to-analog conversion ... ...... ....... ....... .... .. .. twin 1 8 -bit floating Filtering ..... ... .. .... .. ........ .. .... : .... . hi-bit digital & 3rd order active filter I ! Volume control General Dimensions ...... ...... .. ...... ... ......... .. ............ 435 x 120.5 x 418mm Power consumption .... ....... .. .... ........ ................. ...... ....... 30 watts Weight .... .... ... .. ... ....... ... .... ........ ..... ... ......... ....... ... ........ . 14.2kg previous models although it is notably larger and heavier. In fact, it is currently one of the largest and heaviest CD players available. It is made to look even larger by its massive feet although they are not quite as noticeable as they appear in our photograph. As can be seen, the CDX-1110 offers comprehensive facilities although, for remote control, you can directly select any of the first 24 tracks of a disc. For tracks above 24, you first hit the 10 + button twice (or more) and then a button between 1 and 9. (some test discs have over 50 tracks). If you've listened to a disc many times and know it well, you can "freshen" it up by listening in "random play" mode. Three repeat modes are also available. You can repeat a single track, the whole disc or a track excerpt, as marked by two pushes of the A - B button. The latter repeat mode is very fast, with almost no gap between the end and start of the repeated passage. This can be handy for music students or when testing loudspeakers. If you ' re taping a CD, the CDX-1110 will insert a 3-second gap between tracks. This makes it easier for the tape player to subsequently find particular tracks (in those machines with automatic music selection). You can also program the order of play, up to 24 tracks. And how many of you have CDs on which there is a track you really hate? The CDX-1110 copes with that. By using the Delete button you can program it to leave out the track or tracks which are "on the nose". So much for the play facilities. Most users will probably not use the controls on the machine but use those on the remote instead. It's much easier and you don't need 20:20 vision to see the control labelling. the most part, these are in line with those offered on previous Yamaha models. We'll just touch on the highlights of the playing facilities, all of which are also available on the infrared remote control. As can be seen from the photo, you can directly select any of the first ten tracks via buttons on the front panel. On the The Yamaha CDX-1110 is one of the few machines on the market with full volume control via the remote handpiece. It's a beauty. Yamaha make the point that the digital volume control is more precise, offers better tracking between channels and lower noise but I just like it for the convenience. It increases (or decreases) the signal level in 0.4dB steps and has a total range of more than 70dB. The remote control has no less than 44 buttons but it is still quite easy to use although it would be better with a bigger "Play" button. OCT0BER1988 21 18-bit conversion Inside the Yamaha CDX-1110: note the two transformers in the power supply and the large player mechanism which has a locking lever for safe transport. The same could be said of the buttons on the machine itself; the Play button needs to be made bigger or more obvious so that you don't have to peer at the front panel to find it. Output facilities On the rear panel, the CDX-1110 has two pairs of RCA outputs, both of which are variable in level via the digital volume control. One set of outputs is labelled "direct" while the other is "filtered". The difference between the two is that the latter has an analog low pass filter to remove digital sampling artefacts (that is, noise at the sampling frequency). Yamaha state that they have pro_vided the choice of two outputs because some people prefer the "softer" sound of the filtered output while, on the other hand, the direct outputs have the advantage of minimum phase error. In addition to these analog stereo outputs, the CDX-1110 has two digital outputs, for ultimate connection to a separate D-A converter, should a better unit be available in the future (perish the thought). One 22 SILICON CHIP of these outputs is via a conventiomi.l RCA phono connector while the other is via an optical fibre connector, for true isolation. The mains supply connection is via a sheathed two-core flex with moulded two-pin plug. The unit is double-insulated. Interior details Removing the lid of the CDX-1110 reveals a very busy interior with lots of interconnecting wiring between the various printed boards. The power supply is unusual in a couple of respects. It has two power transformers, both quaintly labelled "massive power supply" . The other point is that the supply employs shunt regulators instead of the more usual series regulators. Yamaha state that this is because the shunt regulators have a lower output impedance than series regulators, particularly at high frequencies. The implication we draw from this is that the shunt regulators are better at suppressing digital "hash" and therefore result in a better signal-to-noise ratio. Having covered the key features of the CDX-1110, we still have yet to explain how the unit manages to employ an 18-bit D-A converter instead of a 16-bit converter, oversampling or not. In reality, Yamaha has combined an 18-bit digital filter (which performs the 8-times oversampling) in conjunction with two 16-bit D-A converters, one for each audio channel. Yamaha has taken advantage of the fact that the two most significant bits from the 18-bit filter are only present during the loudest parts of the program signal. Normally then, the top 16-bits of the 18-bit signal are fed direct to the two 16-bit D-A converters. When one or both of the two most significant bits is not present, operation is shifted to accommodate the two least significant bits while the gain of the associated audio amplifier is changed by a factor of 0.25 to compensate for the change in signal level. The result is a much improved signal to noise ratio. This clever scheme is shown in Fig.2. We can vouch for the fact that it works - the CDX-1110 has a phenomenal signal-to-noise ratio. It also has improved linearity at very low signal levels. Interestingly, the way in which the 18-bits from the digital filter are manipulated to make them compatible with the 16-bit D-A converters is not the end of the story. Yamaha use the same technique to provide the remote volume control referred to earlier. To change the signal level, the signal is varied in level while it is still in digital form, by manipulating the bit levels. Very tricky. On test In use, the CDX-1110 is great. The transport mechanism works very smoothly and quitely. And it has the fastest access times we have yet to come across. Switching from track 1 to track 25 on a 25-track disc takes less than two seconds. That's really fast. Sound quality was absolutely tops, from either the Direct or Filtered audio outputs. The difference is very small although it is discernible to the keen-eared Th e top 16 bits are sent directly to the DIA converter DIA converter drops operat,on level by up to two bits to accommodate digital filter output j j : 114 L______ ___ J l Output Gain lowered by 114 High Level Signal Low Level Signal Fig.2: these diagrams show how the 18-bit parallel signal from the oversampling filter is switched to the 16-bit D-A converters (only one shown). When the lower 16 bits are switched to the converter, the output amplifier gain is reduced to compensate for the shifted operation. listener - but only when switching directly between the two. On the test bench, the CDX-1110 really shines. Paradoxically, it presented us with less problems in confirming its specifications than many other CD machines we have tested. The reason is that the digital sampling artefacts are so high in frequency that the normal 20Hz to 20kHz bandpass filter of our AC millivoltmeter ignored them. As a matter of interest, the 352.8kHz residual signal is - 60dB with reading being .005% at 20kHz in one channel. Verifying figures for channel separation was no problem . Yamaha specify - lO0dB. We achieved around - 103dB or better over the whole frequency range. Signal-to-noise ratio Signal-to-noise ratio is the big one. Yamaha specify this at a stunning - 118dB. Six months ago there was no way we could verify this, respect to full output. Yamaha quote the frequency response as being flat from 2Hz-20kHz within ± 0.3dB. None of our test discs go below 20Hz but within the range 20Hz to 20kHz we were able to confirm that the Yamaha's unfiltered outputs were considerably better than ± 0.3dB. In fact, the response was only .03dB down at 20kHz. The filtered outputs were not quite so precise but well within Yamaha's spec of ± 0.3dB. Yamaha's spec for harmonic distortion is a little vague, a figure of .002 % being quoted, with no reference frequency. Our measurements yielded figures very close to or equal to .002 % for most of the frequency range, with the highest All functions of the CDX-1110 player can be selected by the infrared remote control. with available test equipment, commercial or otherwise. Now we can, with our own AC Millivoltmeter. For unweighted measurements (band limited from 20Hz to 20kHz) on the unfiltered outputs, we measured -114dB and - 117dB for the two channels. For "A" weighted measurements, these figures improved to - 116dB and - 118dB respectively. Strangely, the figures were not quite as good for the filtered outputs: - 11 ldB and - 113dB unweighted, and - 113dB and -115dB "A" weighted. That slight degradation may be due to the op amps in the analog filter stages. For those who have just read those figures and find them a little meaningless, let's put them in perspective. That figure of - 118dB with respect to the 2 volt RMS reference signal represents a noise signal of just 2.5 microvolts (2.5 millionths of a volt)! That makes the Yamaha CDX-1110 the quietest piece of audio equipment available, that we know of. Unbelievable. Linearity is another key test of the Yamaha 18-bit technology. If it doesn't come through here, it isn't worth doing. Well it does. On the linearity test tracks of the Technics CD-001 test disc, we measured an error of - 0.4dB at the - 80dB level. At the - 90dB level, we measured errors of between - ldB and - 1.2dB, depending on whether direct or filtered outputs were connected. These results are easily the best we have ever measured. No problems with tracking tests were encountered as far as the test disc was concerned. Nor did we expect any. Well, how would you sum up the Yamaha CDX-1110? Clearly, the objective measurements show it to be one of the best machines available today, regardless of price. And subjectively, it's right up there among the top machines. You'd need to own a really top amplifier and loudspeakers to do it full justice. Recommended retail price of the Yamaha CDX-1110 is $1899. For further information, consult your local Yamaha retailer or Yamaha Music Australia Pty Ltd, 17-33 Market Street, South Melbourne, Victoria 3205. Phone (03) 699 2388. 16] OCT0BER1988 23