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DVD-A v. SACD


RichP714

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Interesting article re the DSD encoding scheme<br />

It is almost impossible to see the daylight through the clouds of format wars between SACD and DVD-Audio. There are too many opinions to clearly find the solution - which format to choose in comparison with CD-DA and LP.

Statistics are not favorable to the new high definition formats today. According to RIAA (Recording Industry Association of America) in 2003 only 0.4 million DVD-Audio disks were sold, 1.3 million - SACD, 1.5 million - LP, and 745.9 million - CD. CD sales reached the peak level in 2000 and are presently experiencing a steep decline. Perhaps the public interest in CD is lowering down because of the phenomenal steady growth of the DVD-Video format - 369.6 million including music DVD in 2003.


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Even now funny incidents sometimes happen: in 2004 in a Circuit City store the sales representative with a serious expression asks clients if they have a special player to play back the purchased SACD disc (note that there is a label "Hybrid" on the disk cover, which shows that the disc also contains a standard recording in the CD-DA format).

It's clear that high definition formats have more capacity to support high quality signals. The question is how great this capacity is and where can we get this superb quality signal from. Is it always present on discs with attractive SACD or DVD-A labels? A lot of argument about the quality of formats lies in this plane.

Birth of Formats

Manufacturers were in such a hurry to offer new formats to the customers that they have made a lot of mistakes on the introductory stage, and thus having created a certain negative attitude to the new medium. Namely:

  1. Some SACD were developed in ProTools, the most widespread development package using the PCM format. To process a DSD steam on the mastering stage they had to convert it into PCM, make necessary changes and then convert it back into DSD. Even if the record quality does not suffer much from a proper DSD to PCM conversion, then at least all advertised theoretical advantages of Direct Stream Digital (that is the direct route of the signal from a studio microphone to the speakers of a listener) is obviously put into prejudice. Besides, the ProTools package in those years was mostly based on hardware processing with algorithms designed in their quality for the output CD-DA format. But if a 16bit 44100  kHz PCM source was used as a master track, the sound quality of the resulting SACD disc could be worse than that of the similar CD record.
  2. The first DVD-A disks couldn't demonstrate superiority of quality either. Despite the fact that most of them were created in 24bit 48  kHz, some of them were in 20bit 48  kHz. But the format evolved, there first appeared 24bit 96  kHz stereo tracks on DVD-A, and then multi-channel 24bit 96  kHz tracks.

    Modern DVD-A Advanced Resolution has a multi-channel track of 24bit 96  kHz and/or stereo 24bit 192  kHz/96  kHz. Moreover, they are usually created from 24bit 96  kHz / 192 kHz master records, all the processing being performed on state-of-the-art equipment with high definition (supporting 64bit 384  kHz), which considerably influenced the resulting quality.

So Which Format is of Higher Quality?

CD-DA format (PCM 16bit 44100Hz stereo) became obsolete long time ago, its limitations do not allow to reach the level, required by today's music lovers. We cannot obviously ignore the incredibly large CD-DA market, which cannot be even approached by SACD and DVD-A. But just few years ago the same thing would apply to the market of video cassettes and DVD-Video discs. Popularity of the CD-DA format and it's ease of use do not allow to predict that this format would end like VHS, but nevertheless, its substantial limitations such as frequent clipping (signal limiting) because of the wish of an audio engineer to achieve a maximum dynamic range, the spectrum limitations (they are discussed in this article below), and new interfaces supporting high definition formats in unfailing digital form to transfer among devices (i-link, HDMI, Denon-link, M-link, etc) make us presume that in the nearest future CD-DA will shift to the mass area, as for example, the mp3 domain, making room in the music lovers' sphere for the formats DVD-A, SACD and WMA9 pro, supporting 24 bit 96kHz multi-channel Audio, promoted by Microsoft. The comparison of multi-channel audio and stereo, their pros and cons is an other story.

In case of correct CD playback (as it is implemented in devices from some High-End manufacturers) and incorrect playback of SACD and/or DVD-A, the former may have higher quality sound, defined in double blind tests (ABX eliminates the placebo effect, or the autosuggestion influence of the listener on the final results), which in its turn served as a battleground for disputes about the quality of high definition formats. Double blind tests are not ideal, though they allow to reach rather acceptable conditions to get statistically correct results. It's strongly recommended to use the free program PC ABX or the free ABX plugin to the well-known program Foobar 2000 to make sure whether we really hear the difference (not just persuaded ourselves that this difference exists) and only then look for the reason.

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Try to record a couple of fragments from CD (it's better to rip the tracks) and record it from the identical DVD-A. Then, using ABX, with high level of probability you will find out the difference (see the details).

The interesting comparison on the quality of DSD SACD and PCM DVD-A had been provided by Craig Anderson. Though he came to the conclusion about the advantage of PCM 24/192 in the accuracy of signal representation, the oscilloscope plot of the 10  kHz square wave demonstrates some kind of identity for results in PCM 24/192 and DSD. Smeared forms of the DSD signal can be explained by ultrasonic noises, the picture was smoothed in time due to pixel latency in the oscillograph screen.

Difficulties in Processing

You should take into account that the DSD format is significantly more difficult to process regarding bass management and time alignment control for sound equalization at the listener's point as well as for acoustic system calibration (acoustics-room). Everybody has been waiting for a DSP to make adjustments in the native form of DSD streams in consumer equipment, SONY announced several new chips (CXD9776Q and CXD9722Q) using the DSD processing algorithms in the brochure ES Series Receivers Technical Background regarding STR-DA9000ES, but ... as a result according to the service manual all these adjustments are processed in PCM domain (in the 9000 model). As we known, this top model does not have the acoustic room reaction calibration feature, though it could have it considering processing in PCM and the availability of similar functions in the closest competitors from Pioneer, Yamaha and Denon (similar calibration is implemented in the 3805 model and we already know the new top model 5805 with the same feature).

Thus, for the time being the DSD format from the point of view of the availability of necessary modern solutions is less interesting to audio equipment manufacturers, and even Sony is not ready to offer full complex of DSD signal processing in its original form on the consumer electronics level.

Analog vs. Digital

LP as a quality data media was knowingly discredited at the CD-DA introduction stage, marketing experts of the companies, interested in CD-DA promotion, carried out mass brain washing. Even today in case of correct playback the LP format is not just ready to compete with CD-DA in audio quality - according to many audiophile's opinions this format often outscores CD-DA. What's the reason?

Some measurements carried out by enthusiast-audiophiles and professionals, give us the ground to presume that the reason is in a wider spectrum and, despite the prevailing opinion about the 60dB limitation, still sufficient dynamic range. Have a look at the LP dynamic range measurements taken by Chris Johnson. You can also see the LP spectrum limitation measurements taken by an Australian audiophile and the author of the reviews on the equipment Chris (Christine) Tham. As you can see, LP dynamic range is close to that of CD-DA, and its frequency band considerably surpasses the latter. It's recommended to read the complete article Spectral and Dynamics Comparisons of LPs vs digital formats.

Another important moment - we can't forget that at the time of CD-DA format launching, the LP recording's analog originals were mostly processed on analog equipment, which practically reached it's peak of development. Digital equipment for CD-DA was not perfect - low DSP resolution for processing (often only 24bit for 16bit CD-DA signal, which resulted in rounding off for the resulting 32bit figures at multiplication operations, and thus, in digital artifacts in the output signal), low sampling frequencies, lack of dithering and noise-shaping, which were added to the CD-DA toolbox later, high level of jitter in digital audio recorders. Some audiophile studios even decided to roll back to analog mastering systems.

All such problems remained recorded on CD, that's why their quality differs so much from specimen to specimen despite the fact that "digit is always digit". However as we known, the same or similar drawbacks are typical of early DVD-A and SACD.

Why do We Need Frequencies over 20 kHz?

We have come to an important stage. One and the same question has been asked on different forums in threads about formats and their quality - if a human being can't hear frequencies over 20 kHz (in rare instances 21 kHz) then the 22  kHz limitation in CD-DA (according to the Nyquist theorem it's a half of sampling frequency, for 44100 it will be 22050Hz) should pose no problems, shouldn't it? Why do we need 50 kHz, 70 kHz, and even 96 kHz, if we don't hear them anyway? And the second point - if our speakers have the stated pass band of 20Hz-20 kHz on the level of -3dB, then why do we need DVD-A or SACD? Our loudspeakers will not be able to reproduce the required spectrum, and moreover, intermodulation products of ultrasonic frequencies may get into the audible region and distort the original signal. Isn't it better don't have these ultrasonic images?

That's what said Nelson Pass, the well-known guru in the audiophile and audio engineerieng society:

"Although human hearing is generally very poor above 20,000 Hertz, ultrasonic frequency roll-offs produce phase and amplitude effects in the audible region; for example, a single pole (6dB/octave) roll-off at 30  kHz produces about 9 phase lag and 0.5 dB loss at 10  kHz. The effects may be subtle, but their audibility is undesirable in a piece of equipment whose performance is judged by its neutrality." (original). Thus, being aware of our hearing sensitivity to phase distortions, we can presume considerable decrease in the level of such distortions in the systems with a wider signal spectrum (including the quality LP playback).

Acoustical Spectrum of Real Instruments

The second point - if we limit the original signal with the analog anti-aliasing filter for the CD signal spectrum in comparison with the same filter for DVD-A 24bit 96 kHz signal when trying to record the spectrum of such instruments as a trumpet, there will be a considerable difference in phase distortions between the original and the record even before it is delivered to the speakers. The speakers (well-designed) have mildly sloping signal falloff characteristic at high frequencies, which mostly depends on the tweeter design, and thus introduces fewer phase distortions than the filter with a steep amplitude-frequency response falloff, which is in fact the CD-DA format for the wideband spectrum signals.

Scientific Analysis of formats

And what does the science say about the sound difference in DVD-A and SACD in comparison with CD-DA and the reasons for such differences or their lack? Let's take a look at Dr. David Griesinger's presentation. Together with Jim Fosgate he is one of most known scientists in the multi-channel surround sound theory, the man who created and developed Logic7 (Lexicon's proprietary surround sound processing algorithm).

This respected professor conducted serious research and found out that very often DVD-A and SACD discs do not contain the advertised ultrasonics. He surmised that we hear the difference due to intermodulation products in high frequency speakers that get into the audible region. Professor refers to the work "Karou and Shogo "Detection of Threshold for tones above 22 kHz". Yes, we cannot really hear ultrasonic images over 20 kHz. But the above mentioned work was carried out for the signals with even order harmonics and the audible odd order harmonics produced due to the transmission nonlinearity in the device. Having eliminated the nonlinearity and thus the odd order harmonics (in fact the odd order harmonics only testified to the appearance of intermodulation products due to this nonlinearity in the audible region) the ultrasonics became inaudible (that is there disappeared not only the odd order harmonics and the intermodulation products as well). That's the way it should be, because we cannot hear ultrasonic signals of the sine form.

In the presentation Dr. Griesinger provides the information concerning some difficulties in finding of the acceptable soundcard for the experiments. If we will tale a look at the noise ground level in the used soundcard, it looks like it is still not acceptable. With a better soundcard the results could be different.

Signals of -3dB and 20 kHz and 25 kHz transferred to the speakers. We should expect intermodulation and clipping (in majority of cases) on these levels and frequencies in consumer-grade devices, we need to use professional devices to avoid them (able to pass CCIF measurements at such levels, for example my old Audigy produces clipping an the -6dB level using 19kHz and 20kHz). Please pay attention to the noise floor that you can see on the spectrograms in the high frequency region. With the used combo (player + sound card) it reaches -90dB. Thus: the audible products of intermodulation distortions are due to the amplifier (not because of the speakers).

Then several specimens of SACD and DVD-A had been examinated, measurements demonstrated that these discs DO NOT contain ultrasonics over 23 kHz. Interestingly, the noise groundfloor at the graph in DVD-A Steely Dan reaches -72 dB (strange kind of DVD-A - it's noises exceed the CD-DA limitation by several dozens dB), and the SACD noise groundfloor is a bit better, but it still reaches -78 dB! But we DO really HEAR the excellent sound quality of the records on these discs.

It was decided to use the available specimens Steely Dan "Two Against Nature" DVD-A and SACD multi-channel Diana Krall for the re-test.

Repeating the Measurements

The author of this article carried out quality measurements using a top-level professional sound card Lynx L22 (dual channel version of the sound card Lynx Two), which is probably the best tool for similar measurements (the "measurement" function is noted in the card's specification) at the level below professional measuring equipment such as AP. The obtained results were somehow different then the previous ones.

In our re-tests we got the supposedly lacking ultrasonics in the 25 kHz - >35  kHz range at the levels up to -50dB for the same DVD-A and SACD:


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Spectrogram of the fragment from DVD-A Steely Dan "two Against Nature",
The blue color - multi-channel mode, yellow - stereo


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Statistics for DVD-A Steely Dan "two Against Nature",
on the left - multi-channel mode, on the right - stereo


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Spectrogram of the fragment from SACD Diana Krall,
blue - multi-channel mode, yellow - stereo

On the spectrogram we can see that the lower noise border is at -132 dB for the multi-channel track. The suggestion concerning the significant difference in the results in not only in the the sound card quality. The possible reason is that the device (DVD/SACD-player) filtered the output signal and that multi-channel and stereo tracks contained different signals, we will provide some information below to support such kind of statement.

Indirect proof to this assumption are the measurements, taken in the lab of the Stereophile magazine, which revealed relative similarity of the CD signal on the hybrid track with the SACD stereo signal for the well-known multi-channel SACD "The Dark Side of The Moon". You can see that they are almost identical, but the multi-channel track differs considerably from the stereo one (two images below are illustrating the aforesaid):


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Spectrogram of the fragment from SACD "Dark Side of the Moon":
red - multi-channel mode, yellow - stereo


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On the sonogram: on the left - multi-channel mode, on the right - stereo
On the spectrogram: red - multi-channel mode, yellow - stereo

Measurements were taken as accurately as possible - samples are matched on the corresponding signal peaks and levels (one of the signals is amplified in Adobe Audition 1.5 with resolution of processing at 32bit floating point 96 kHz) and only then followed the comparison.

The similar situation is with the other multi-channel SACD James Taylor "Hourglass" 1997, song "Line ‘Em Up" and with all the rest. You can see on the picture how different the signals are on these tracks - beginning of the same fragment in the channel of the corresponding level:

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Fragment from SACD James Taylor "Hourglass",
comparing the line-out signal from the player and the receiver,
in the multi-channel and stereo modes

As it's difficult to assume that the THX-processing adds some nonexistent ultrasonic signals to real multi-channel tracks, it looks as to all appearances they really exist on the tested SACD and DVD-A discs. Though not all devices could reproduce them. And here we come to the important point - the problem is not with formats, the problem is with their correct playback! This point is supported by the measurements.

We are very thankful to Dr. David Gresinger for his presentation, which supplied an idea to create this article. There is a significant amount of useful information concerning multi-channel surround sound at his website.

Dependence of the Quality on a Playback Method

In fact, there has been a common opinion strongly supported by marketing people from the SACD camp that the correct method for reproducing of DSD signals is via a simple analog filter (it allows to get rid of "unnecessary" additional conversions from the digital to analog form) or using delta-sigma digital-analog converters. You can see on the picture below the result of such playback using analog filters in the relatively high quality PCM1738 DAC:

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Fragment from SACD James Taylor "Hourglass",
yellow - DSD signal directly to DAC of the PCM1738 player,
blue - transmission via i-Link and then further to PCM and DAC of the PCM1704 receiver

High frequency and level noises create intermodulation interference in the audible region, plus phase distortions due to sharp spectrum edge at 22 kHz allow to guess the difference 19/19 in double blind tests, that is with 0% chances of guessing. Note that the signals were aligned by their levels and were practically identical by sight at the frequencies up to 18 kHz (the picture above contains the same sample).

Thus, we can nevertheless hear ultrasonics (not separated from the original audible signal), and the noise level, which is considered inaudible for SACD-signals, plays its role, because these high level noises create intermodulation products in the audible region (of the same random order as the noises) can influence the sound transparency and the perception of low level reflection signals.

What is the Correct Way for SACD Playback?

How can we play back SACD correctly? We can agree to well-known Russian engineer Dmitry Andronnikov, who expressed the idea to convert the DSD-signal to PCM and then reproduce this signal via multibit DAC. This approach is implemented in the AX10 (49TX) receiver and then used in all top receivers from Pioneer. What's the reason, why do we get better quality with seemingly extra "additional conversions"? The point is in reduced distortions (it sounds as a non-sense, but please don't make fast conclusions) due to these additional conversions. In fact the point is in DSD->PCM converters (for this purpose they usually use SM5816 or in the new devices - SM5819A), which in fact are high quality digital filters operating at the frequencies 2Fs and 4Fs in the aforesaid devices, which filter all high frequency noises in SACD at the level of -130dB not allowing these noises to create intermodulation products in the audible region and to "overload" the operational amplifier with HF components in I/V after DAC. Using a digital filter before DAC, operating in the oversampling mode, we cut-off the remains of HF interferences from the DSD steam achieving for the SACD signals the same quality as for DVD-A of the high definition. Top Pioneers use multibit (Sign-Magnitude) PCM1704 as DAC, the top receiver Yamaha Z9 contains a new multibit delta-sigma DAC PCM1792, which allows to compare playback modes via DSD->PCM conversion (the same SM5819A is used for such purpose) or via analog filters (implemented in PCM1792) as it was done for PCM1738. However, after all our measurements the result is predictable.

Dmitry's hypothesis is supported by the fact that in the new digital top receiver Sony STR-DA9000ES the entire signal processing is done in the PCM format, the DSD circuits after the DSD->PCM conversion are not used, and the corresponding chip pins are grounded (DSD to PCM conversion is up to SM5819A, which is re-bandged by Sony as CXD9742).

Pay attention to the difference in noise levels and spectra when playing back multi-channel tracks and stereo tracks from the same discs . You can see that the common stereo tracks are created from stereo sources, often with a pass band limitation at 22 kHz or 24kHz and a considerably higher noise level. Multi-channel tracks, which are usually completely remastered or recorded anew from the 24bit 96 kHz original master sources, feature quite a different signal quality. In one's time many people discovered an essential difference in quality when playing back SACD multi-channel Dark Side of The Moon using multi-channel and stereo tracks (SACD in both cases), but after our measurements we already know the reason.

Thus, multi-channel systems and the THX sets of the speakers are much more interesting than it used to be considered, but that's another story.

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And more from ESP:
 
Introduction

For a while I have been interested to find out how good the new high resolution formats Super Audio CD and DVD-Audio really are? I have visited some demonstrations, but not been impressed which may be due to other causes than the sound formats.

After reading many replies at different forums, it seemed like many audiophiles considered SACD to be better than DVD-Audio. I also thought so until recently read what Ing. Öhman wrote in the Swedish Audio Technical Society * journal.

  • (*
A non-profit organisation for sharing interest and knowledge in audio and sound reproduction) The following are quoted from what Ing. Öhman wrote in the journal:

 

"It is nothing less than a tragedy that Sony/Philips system SACD still is considered to be a real competitor to DVD-A, though it has lower real resolution than the CD-system in the highest octave.

DVD-A does absolutely offer a much higher dynamic range than CD, but it is very questionable if SACD does.

SACD is in the high frequency range quite mediocre, even compared to a good CD-system one-bit DAC, and of course clearly inferior to a CD-player with a real multi-bit converter.

On the contrary, DVD-A is in theory 250 times better than the CD-system at all frequencies!

In today's reality though, it is hard to achieve such hyper-resolution, but maybe in the future? If the potential exists, recording and playback technology can evolve. Today the DVD-A resolution is about 16 times better than the CD-system and the bandwidth extends up to 100 kHz to be compared with 22,050 Hz for CD."

Now I became curious! This is the opposite of what I thought. I asked Öhman for a follow up ...


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 too 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 JVC's 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 multi bit 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 multi bit-converters?

 

IÖ: Though some fine multi bit 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 over sampling 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 Hi Fi-magazines and Hi Fi-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 "psychoacoustical 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 comparisons 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.

NL: Thank you for your time and for answering my questions!

IÖ: Hope I could straighten out some of your question marks.


Editor's Note

This article is reproduced with the kind permission of Niklas Ladberg and Ing. Öhman, with translation from Swedish into English by Marten Kihlberg. No changes have been made to the text other than by way of translation, and the actual words used herein are as accurate as translation allows.

The editorial "content" has been limited to the creation the web page (in standard ESP format) from the original article, a small number of grammatical corrections and the addition of one word [power], when referring to the noise level differences between SACD and DVD-A (i.e. 20,000 million is the power difference, not voltage difference).

I would like to thank Niklas Ladberg, Ing Öhman and Marten Kihlberg for making this information available.

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