Newsgroup: it.hobby.hi-fi
Titolo: SACD technical info

Scioccante?:
Ciao
berry
Niklas Ladberg: How did you come up with these conclusions?
Ing. Öhman: DSD (the coding technique used in SACD) is much better than 
CD in the low frequency range. The problems occur at higher frequencies. 
The noise level in the ultrasound register is more than 100 dB higher (-
40dB under maximum output level, using narrow band analysis) when 
compared to DVD-A (-144dB under maximum output level, full spectrum 
noise).
Another way to describe the difference: The noise [power] from SACD is 
more than 20,000 million times higher than from DVD-A!
But maybe it is more relevant to know that this ultrasound noise from 
SACD is enough to warm up the tweeters voice coil with some detectable 
influence on reproduced sound. Besides, the ultrasonic may also affect 
the audible sound by down mixing in the air, at least at higher sound 
pressures.
A comparison with CD is harder because of the limited bandwidth of the 
CD-system. Signal to noise ratios in the range above 22,05 kHz can 
therefore not be determined, but noise level from CD can be as good as 
DVD-A – one can always use low pass filter! Then no ultrasound comes out 
from the CD-player.
The problem with SACD can be shown by theoretical calculations, 
measurements and by listening. I have done lots of all these three and 
every one of them points clearly in the same direction: SACD has not 
more resolution than CD above 10kHz. Our early estimations some years 
ago have now been confirmed by measurements and listening, made both by 
us and others. Today, many studies have been done, for example by 
Stereophile who has tested SACD players several times and confirmed our 
estimations.
NL: What does Stereophile say about the limitations of SACD?
IÖ: Oh, not much in the written tests. Stereophile is an advertisement 
dependant paper and they are a bit careful to say anything negative 
about anything, but they present their measurements, often done by the 
sharp editor in chief John Atkinsson. His comments are very informative! 
Although very careful, any equally sharp reader can decipher Atkinson’s 
opinion from the text.
Stereophile also performed a large subjective listening test between 
some existing high performance recording formats and SACD was even 
considered to be inferior to PCM 16bit, 176,4 kHz.
Anyway, one should not take too much notice of "how many" said this or 
that. What is important is how things really are, not how many people 
believe this or that. Deciding truths by voting is seldom a good way. It 
can only show what people believe. Some peoples beliefs might of course 
be right, but to often correct information and relevant listening 
experiences drowns in common misconceptions, preconceived notions and 
the media background noise.
This happens especially easy in this particular case since DVD-A and 
SACD never have been compared under equal conditions.
NL: I read in a technical paper about SACD. Sony writes:
"The vast majority of A/D-converters used in PCM recording for 
conventional CD are 1-bit converters with high sampling frequency"
Then it must be better to keep the signal in DSD-format (SACD) than 
convert the signal to PCM (CD/DVD-A)?
IÖ: Yes, that is correct, but is it relevant question? The CD-system 
seems worse than it is when used with a one-bit converter. The problem 
is not the conversion from a one-bit converter to PCM but the one-bit 
converter itself!
Besides, the one-bit converters used in CD-players usually have higher 
resolution than DSD, which only samples 64 times faster than CD-system 
sample rate (i.e. DSD sampling rate = 2.8 MHz). The low sampling rate in 
DSD is used because of the systems ineffective coding and lack of 
storage space. By packing the information it becomes a bit more 
effective but it still is ineffective compared to PCM.
One-bit converters for CD-players often use sampling rates between 11 
and 50 MHz. The best one-bit converter probably is JVCs PEM-DD and it is 
much better than DSD. This said with reservation, I might have missed 
some even better one-bit technology than PEM-DD. But as far as I know 
this is the technology that comes closest to true multibit technology in 
resolution.
NL: I presumed that SACD uses DSD-technique for recording and mastering, 
but that turned out to be wrong:
Press release: "A big surprise at the AES was the confirmation by Sony 
that DSD technique, used in SACD, uses multi-bit PCM during recording 
and mastering processes and that only uses one-bit technique as it 
applies to consumer playback systems. Jim Johnston of AT&T Research 
speculated that DSD and DVD-A data streams might be able to co-exist if 
output from different points within the same microprocessor."
Apparently they use PCM for recording and mastering, even for SACD. Now 
the advantage of no conversion between formats suddenly disappears.
IÖ: Several documents show this is the case. Sony/ Philips has even 
officially recommended using PCM when editing the recorded material. I 
think it is a wise recommendation, because every manoeuvre in the PCM-
domain is straightforward, easy to make and will not degrade the quality 
if performed with high enough resolution. Only the DSD-problems remain!
Therefore DVD-A is a purer and more straightforward system. No 
conversion between different formats and 144dB resolution at all 
frequencies up to 100kHz. Could it be better? Well of course it can, it 
can always be better, but DVD-A is good enough. DVD-A is what the CD-
system should have been from the beginning!
NL: Back to the Sony technical paper:
"On the playback side, most CD-players utilise one-bit D/A-converter to 
convert digital signals back to analogue."
Is this correct? Don’t most CD-players utilise multibit-converters?
IÖ: Though some fine multibit CD-players exists, unfortunately most CD-
players today utilise one-bit converters. It is probably a price 
question. A so-called 24 bit one-bit converter (working with one bit 
technology inside but accept 24 bit input) costs about 2-4 dollars 
including 2 channels and digital filter.
A real 24 bit converter with 96 kHz sampling frequency and 8 times 
oversampling costs about 10-15 dollars per channel – without the digital 
filter. For two channels and digital filter it ends up to approximately 
40 dollars.
So multi bit technology is ten times more expensive as one-bit 
technology. Most manufacturers find it easy to choose ... Especially 
since HiFi-magazines and HiFi-stores never take a stand and point out 
the difference.
NL: From Sony again:
"Although the bit numbers is just 1/16 of that used for the CD-format, 
the sampling frequency is 64 times higher. DSD can accommodate more than 
4 times the information as the current format."
4 times more information could not be wrong? Or is the depth of bits 
more important?
IÖ: The number of the bits is much more important. Actually the DSD-
system is theoretically less dense in information than the CD-system. 
Even when the data is packed (as it is on an SACD) it is still not much 
better.
When Sony declares that DSD-format can store 4 times the data, they 
probably mean that there is 4 times the space on the SACD-disc compared 
to CDs. But since the DSD-coding is so ineffective, the real information 
is considerable lower.
The resolution/ information doubles when you double the sampling 
frequency (it is possible to be more specific, but for this example it 
is enough). But to double the resolution using PCM, you only have to add 
one more bit. If you go from 1 to 16 bits (adding 15 bits which use 
approximately 15 times more storage space), the resolution increases 
65,536 times (from one step to 65,536 steps).
There is also another essential difference; the increase in resolution 
you achieve from raising the sampling frequency will be frequency 
dependant. A one-bit system will therefore have high resolution at low 
frequencies (where the information theoretically is low) and have low 
resolution at high frequencies (where the information theoretically is 
high).
By the use of noise shaping of high order, it is possible to increase 
the resolution at "quite high frequencies" at the expense of resolution 
at very high frequencies, but only for static, non transient signals. 
Transient signals will have poor resolution in a one-bit system. If the 
signal does not endure for a long enough time, the error will not be 
minimised by the noise shaper of the one bit system.
That’s why you can read in documents from Burr Brown (who manufactures 
both one-bit and multi-bit converters) that you should use multi-bit 
converters for "waveform synthesis applications requiring very low 
distortion and noise". They have not written this for nothing.
A one-bit converter (i.e. the DSD system) cannot regenerate a short 
pulse with stringent form. It will change form from moment to moment. 
Every identical recorded pulse will show up with a new form.
One can always discuss the audibility of such behaviour, and if it is 
audible, one can discuss how much it disturbs. Objectively good 
reproduction is not important for everyone. So if the presentation of 
music is changed in some way, some people might see this as a minor 
problem, others think it is more serious.
It is beyond discussion that the lower resolution of one-bit systems is 
a problem under circumstances more precision demanding than audio. When 
you need both super precision and stability, when you need to know that 
a generated waveform looks like it is suppose to, nothing but multi-bit 
converters will do.
My entirely personal opinion/experience is that audio actually demands 
very high precision, and that the reproduction suffers from the lack of 
precision from one-bit converters and the DSD-system.
Perhaps I even prefer the old 13-bit PCM-based Denon system from the 
70s. It was not a super high-resolution system, but it was as stable as 
it was consequent! I have a lot of these recordings (reissued on CD) and 
they actually sound fabulous!
NL: From Sony’s paper:
"In general, the quantisation noise floor resulting from PCM is flat, 
according to the number of bits. With Delta Sigma modulation the noise 
floor is subjected to noise shaping. Because the DSD method uses a high 
sampling frequency, the quantisation noise is shifted to a higher 
frequency range. This reduces the amount of noise in the audible range 
for humans, which is relatively low."
Is this correct?
IÖ: Yes, the first part, but one should be careful not to underestimate 
the hearing, as Sony does – or you end up with systems like SACD!
Of course we can only hear single tones up to 20kHz but this does not 
implicate that we can allow any kind of noise pollution above this 
frequency. Multiple tones in the ultrasound can create clearly audible 
phenomenon at higher sound pressures.
It can be discussed if we can tolerate the ultrasound noise generated 
from SACD. The noise from SACD just above 100kHz is higher in level than 
most of the treble in the audible range, at least when listening to the 
majority of acoustical music. It can also be discussed if DSD uses a 
"high" sampling rate. But apart from that: Yes, without noise shaping it 
will not work at all and that would be a lot worse. Now it is only a 
little bit worse than CD in the highest treble.
But why introduce a new super high-resolution system, that is "a little 
bit worse" than CD? Of course there are advantages when compared to CD 
also, but the drawbacks of SACD/DSD are completely unnecessary. 
Shouldn’t a new system be better than CD in all aspects?
The noise level in the range above 100kHz is –40dB under maximum signal 
level (and is thus even visible on an oscilloscope!). The noise is in 
fact much higher than any possible music signal in the same frequency 
range. This can be compared to DVD-A where the noise level is –144dB in 
the whole audible range and also in the ultrasound range.
In reality these figures have not yet been reached in commercially 
available DVD-audio players, but the potential for future improvements 
is there. Today, the best DVD-A players reach a signal to noise ratio of 
about 120dB (0 – 100 kHz). The figure will be even higher when measured 
with small band analysis. This is far from 144 dB, but still very good.
I think it is a little embarrassing that no good DVD-A recordings have 
been released so far. They have all been of inferior quality. This has 
of course not made it easier for ordinary people to make a relevant 
opinion about the differences in the systems. The SACD recordings from 
Jan-Erik Persson at Opus3 are far superior everything released from DVD-
A.
Now, when looking at "recordings in holistic view", the debate of the 
storing media/system is much less important than the skills of the 
recording engineer – a good recording stored on compact cassette is far 
superior to a bad recording stored on DVD-A. But every debate has its 
time and place. It is not relevant to point out more important issues 
when we are about to choose a new storage media.
This time the storage media (SACD versus DVD-A) is the question, and it 
can very easily be distorted by comparing the systems on different 
recordings. The better recording will always win.
The music is even more important of course, than the recording, but it 
is entirely subjective – not much to debate about. As an example; my 
taste in music is disputably deplorable. At least according to some 
people!
NL: I continue to read from the press release:
http://tinpan.fortunecity.commarrfield/216/pag_eng/oct2000.htm
)
"The watermarking issue is having a big impact in the 109thAES 
convention at L.A (for the moment only at professional level, but in a 
future also at a domestically level). A big and increasing number of 
professionals have pointed out the fact that the actual methods of 
watermarking introduce sound quality degradation into the supposed high 
quality recording formats. While the watermarking promotion groups are 
pushing hard these methods, a group of very well known audio firms 
(Chesky records etc) and well-known engineers (Tony Faulkner of GRP) are 
very disappointed of what they consider an audible degradation of the 
sound quality. The first tests conducted recently in UK and USA (btw, 
not as impartial as supposed to be due to the use of ultra low quality 
recordings) using DVD-audio with the watermarking, have shown the fact 
of this degradation."
Is the watermarking of SACD sound degrading?
IÖ: Well that depends on which watermarking is used! The so called 
"psycoacoustical water markings" are all sound degrading in various 
degree and are not associated with any specific storage system. 
You can use it with any system of your choice, but it is unclear to what 
extent they are used in respective system. As far as I know, no released 
SACD recordings have used this type of watermarking, but I can be wrong.
The only thing I know for sure is that lots of CD-recordings have this 
kind of watermarking. But watermarking is a separate problem. It has 
nothing to do with the either of the recording and storage systems. You 
can choose not to use it. But the problems built in the DSD-system 
cannot be excluded!
Just to avoid misunderstandings I want to make a reminder that SACD has 
higher resolution below 5-10kHz than the CD-system. Exactly where the 
limit is, where each system (CD or SACD) is better, depends on if you 
are looking at a static or dynamic signal.
At frequencies below 100-600Hz the SACD-system could theoretically be 
even better than DVD-Audio, but in reality this is not important. We are 
talking about so small flaws, far below the hearing threshold, so they 
can be disregarded. Any specific player however, can be very bad at low 
frequencies, but not due to the system if SACD or DVD-A is used.
Anyway, in the practical life, it seems like DVD-A wins over SACD at all 
frequencies, cleaner sound, lower noise, and a completely stable system, 
free from potential noise shaping algorithmic oscillations. 
NL: How close to the potential resolution do we come with the player 
existing today?
IÖ: If we look at the players you can buy today, then the resolution is 
about 15-30 times lower than the full potential of DVD-Audio. That means 
8-16 times better than the CD-system. A big improvement, but still a lot 
more is possible.
All these comparations between systems made in "times" are based on pure 
technical specifications. If you want to have "worst case" audibility, 
take the logarithm and multiply it by 20, then you get the figures in 
dB. "15 times better" corresponds to a 23.5 dB lower noise level.
If these figures should be of any use for you, you must have a feeling 
for "how it sounds when an error signal changes X dB below the music 
signal". If the changes of the error signal take place below the 
threshold of hearing, naturally you will hear no difference at all.
Also, different errors have different audibility. Some are easier to 
detect. Others are more difficult. Some faults/errors are therefore more 
tolerable even though they are higher in level.
Who said it is supposed to be easy to form relevant opinions?
Relating technical performance to the experienced sound quality should 
be done with utmost care. My experience is that the quality improvements 
coming from using more bits are valuable only for high dynamic music 
material. An 11-bit recording will do fine for extremely compressed 
"radio-sound".
How people experience sounds in the ultra sound region seems to be quite 
individual. The most sensitive listeners seem to manage music better 
with no ultrasounds/ overtones at all, than with music plus ultrasound 
pollution. Probably no one minds a nicely reproduced ultra sound range 
(like in DVD-A), but when using such a very capable system, there is no 
guarantee that recording engineers manage to keep the ultra sound 
"unpolluted".
When it comes to comparing CD, DVD-A and SACD against each another, it 
becomes much easier, because at optimum implementation, all error 
signals in these systems are in the form of noise. But you have to look 
at every frequency register alone, since the noise character of each 
format displays different spectral behaviour. I mention this again as I 
might not have been clear enough earlier in the text.
-- 
"Sebbene queste siano le mie piu'sincere e personali opinioni di
appassionato, sono un venditore. Ascoltate sempre e non basatevi
unicamente sui miei giudizi"
Ciao
be...@soundberry.com

considered to be inferior to PCM 16bit, 176,4 kHz.
Se leggete Audiophile Sound di questo mese, c'č un interessante
intervista al proprietario della Channel Classics.
Egli afferma, tra le tante cose che riguardano la sua casa
discografica, che la Philips ha costruito un suo convertitore
proprietario che opera dal DSD al PCM 24bit; il risultato ottenuto
rende molto di piů delle stesse registrazioni effettuate direttamente
in PCM 24bit.
A chi dobbiamo stare a sentire?
Io intanto mi fido delle mie orecchie, come ho sempre fatto, esse non
mi hanno mai tradito. Ebbene, ragazzi, non c'č storia, il SACD č un
passo decisamente avanti a qualsiasi altra cosa mai ascoltata fin ora,
DVD-A compreso....
Ciao,
Francesco 
--------------------------------------
Amicitias et tibi iunge pares


Pur non avendo ancora una esperienza d'ascolto sufficientemente completa,
questa č l'opinine che mi sono fatto anche io. La mia piů ricorrente
sensazione, confrontando il SACD con altri formati digitali, č la mancanza
di quella che chiamiamo fatica di ascolto.
Ciao
Andrea

di quella che chiamiamo fatica di ascolto.
Per l'appunto....! (faccine)
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Che scioccante e scioccante, lo sapevamo da un pezzo, IGNORANTONE!.
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