This is only a preview of the October 1988 issue of Silicon Chip. You can view 46 of the 100 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "High Performance FM Antenna":
Articles in this series:
Items relevant to "The Classic Matchbox Crystal Set":
Articles in this series:
Articles in this series:
|
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
|