DSD comparison to PCM.

[opus111]

To me that response reads like classic marketing bluster and obfuscation. 'Our DAC is so different the normal rules do not apply' is special pleading.

 

[Bruce B]

To me that response reads like classic marketing bluster and obfuscation. 'Our DAC is so different the normal rules do not apply' is special pleading.

That may be, but all I know it's the best DSD DAC I've heard.

 

[opus111]

My comments weren't intended to imply it can't sound good Bruce. I fully accept your listening impressions.

 

[Bruce B]

My comments weren't intended to imply it can't sound good Bruce. I fully accept your listening impressions.

Well that seems to be the stance of the majority that has read the measurements. That's why I don't buy equipment based on listening with my eyes....

 

[DonH50]

Well, there's four possible scenarios for the JA's measurements of the MPS-5:

1) Defective transistor in analog section. If a bipolar transistor is damaged by heat or a voltage transient, it can become noisy (which precedes failure). The noise is characterized by bursts, growing worse over time. If the following stages are DC-coupled, the power amplifier can be destroyed by the DC pulses, and the woofer in the loudspeaker will also be damaged. (Even pro woofers can only tolerate 1 watt or less of DC offset, since the voice-coil cannot cool itself by moving back and forth.)

2) Unstable regulator; these can slide in and out of oscillation in the 1~10 Mhz range, and scopes don't easily trigger on bursts of oscillations. RF oscillations makes analog sections do bad things that resemble noise but aren't. Another possibility is a noisy Zener diode that's used as a voltage reference; these are usually bypassed with a cap to lower noise, but the cap might have gone bad.

3) Sub-optimum noise-shaping algorithm in the Playback Designs. This is consistent with the high level noted - no better than 16-bit resolution - but is not consistent with the 3 dB difference in noise levels between channels. You'd expect the algorithm to be the same between both channels. What is consistent with this hypothesis are the noise bursts - 1-bit converters are known for instabilities in the noise-shaping algorithm.

4) JA messed up the measurements somehow. There are many ways to induce ground loops in a measurement setup, and the low levels being measured will reveal this kind of thing. Bad connections in particular will show bursts of noise. Not sure if this would account for the 3 dB difference in noise level between channels, though.

In the absence of more information from either Atkinson or Playback Designs, it's hard to tell what happened. If the noise bursts - which is the most unsettling comment by JA - appeared in both channels, it's the noise-shaping algorithm. If it appeared in only one channel, then it would almost certainly be a bad transistor (or Zener diode). Unstable regulation could appear in one or both channels, depending on whether the MPS-5 shares regulation across channels or not.

The power-supply rails would have to be measured to confirm supply stability, and in the absence of a schematic or a board layout guide, not something you'd expect JA (or any reviewer) to do. Poking around randomly on a circuit board without knowing what you're looking at is a great way to short out a regulator and damage the review sample.

Great post!

A bad coupling (or decoupling) cap would also do it...

 

[opus111]

Well that seems to be the stance of the majority that has read the measurements. That's why I don't buy equipment based on listening with my eyes....

Listening and measurements are almost entirely separate things - that is barring gross stuff like FR. Until we get decent measurements ears are the only reliable test.

 

[LynnOlson]

There were three serious problems in JA's measurements, at least one of which strongly indicated a defective sample. I'm not manufacturing a product (at present), but if I saw measurements like JA's, I would plead with Stereophile to delay the review, pending getting the magazine a replacement sample that was working correctly.

But ... then we get into the politics of dealing with a very powerful, well-financed magazine that has the power to bankrupt manufacturers if they choose to. Although Mr. Tinn's response is, well, non-responsive, it's always a losing game for the manufacturer if bad stuff appears in a powerful magazine. For all we know, Playback Designs may well have seen JA's measurements, responded with alarm, offered to replace the review sample, and Stereophile declined, running the review as-is. We have no way of knowing what happened here.

This kind of thing happens more often than you might think. The short production runs of high-priced audiophile equipment works against comprehensive QC procedures, especially if there are frequent production updates. Magazines can be forgiving, delaying and re-writing reviews to allow for replacement of defective products, or they can be hard-ass, slamming the manufacturer hard. This review seems to fall in the middle; nice subjective review, and a heavy slam on the objective side.

(Don't kid yourself about the impact of JA's measurements; it will definitely cost Playback Designs sales to Asia. Many Japanese, Taiwanese, and Hong Kong buyers are electronics entrepreneurs with design, test, and manufacturing experience. They know perfectly well what a 3 dB difference in noise between the channels means - a defect somewhere.)

 

[Orb]

Lynn,
JA is pretty honest and if he felt it was defective or it was offered to be replaced he would mention that (has done in the past for other reviews-measurements).
Did anyone contact JA regarding this review and measurements?
Cheers
Orb

 

[microstrip]

I do not own a PB, and the only time I had it for a few minutes in my system I found that it sounded nice but that it was not a synergistic match it. However I have now read the review and I am astonished that a magazine can go on testing an unit that has such large differences between the two channels - surely it indicates a faulty unit. Even by tubed ARC CD8 shows a better matching between channels. JA reaction is bizarre at less:

Early on in the testing of the Playback Designs MPS-5, worried that there was something wrong with our review sample, I took the cover off to check that all the ribbon cables were seated properly (they were) and that there was nothing obviously adrift (there wasn't). Did he expect that just taking the cover off he would find the fault?

 

[Ragnar]

Did he expect that just taking the cover off he would find the fault?

A call to the manufacturer would have been the proper response. Something was wrong with the unit and something fishy with that review.

Lynn is correct that the small manufacturer is at risk submitting its creation to a reviewer. It's like playing the lottery but may be necessary to get exposure.

 

[Bruce B]

Also the unit has gone through 2-3 software updates, so the measurements are completely different now. The USB-X is available now as well.

 

[LynnOlson]

A call to the manufacturer would have been the proper response. Something was wrong with the unit and something fishy with that review.

Something went wrong with both the product and the review process. Rene's description is the correct protocol to follow: if the reviewer, armed only with a review sample and test gear, suspects a problem, a call to the manufacturer is strongly indicated, no matter how good it sounds.

Even a highly skilled digital/analog designer is going to have trouble tracking down a problem in the absence of a schematic, a theory-of-operation description, and a board-layout diagram. If the designer is persistent enough, yes, it can be done, but that amounts to a third-party analysis, debugging, and repair/re-design, something most engineers won't do for free, and is beyond the skill set of a magazine reviewer. That's why it needs to go back to the vendor, who presumably understand their own product.

It's inconvenient for the reviewer and magazine to do a re-schedule in the review pipeline, and kind of nerve-wracking for the manufacturer during the intervening months, but products with defects need to go back to the vendor until the problem is resolved.

Skipping over the problem in the review (by not mentioning that the measurements strongly indicate a manufacturing or design defect), or denying any problem exists at all, isn't helpful to anyone. This is engineering, after all: problems are real, measurable, and correctable. That's the point of engineering.

 

[LynnOlson]

Dawn, with the moon setting over the Rockies, looking west. Olympus OM-D, Panasonic 45-200mm lens, Photoshop CS5.

 

[LynnOlson]

Taken a few minutes later, as the sun clears the horizon and illuminates the mountains.

 

[Glory]

The *irony* shouldn't amuse you because I came to my conclusions based on listening to all of the formats in my home. I didn't come to my conclusions based on hearing one format while looking at a spec sheet for the other formats and making a decision on which one I thought sounded best.

How true. DSD is way better than Redbook/HiRez. in my system and who cares if folks want to say other wise. Send all the DSD files you think are less to me.

 

[Ragnar]

How true. DSD is way better than Redbook/HiRez. in my system and who cares if folks want to say other wise. Send all the DSD files you think are less to me.

Come the resolution, all bets are off. http://www.whatsbestforum.com/images/smilies/smile.png

(Sorry, Anon., for the misquote.)

 

[Ragnar]

How true. DSD is way better than Redbook/HiRez. in my system and who cares if folks want to say other wise. Send all the DSD files you think are less to me.

Come the resolution, all bets are off.

(Sorry, Anon., for the misquote.)

 

[Ragnar]

Thanks for the great pictures, Lynn. But it looks like there wasn't much snow in your back yard.

 

[c1ferrari]

But ... then we get into the politics of dealing with a very powerful, well-financed magazine that has the power to bankrupt manufacturers if they choose to. Although Mr. Tinn's response is, well, non-responsive, it's always a losing game for the manufacturer if bad stuff appears in a powerful magazine. For all we know, Playback Designs may well have seen JA's measurements, responded with alarm, offered to replace the review sample, and Stereophile declined, running the review as-is. We have no way of knowing what happened here.

Lynn,

Have you considered asking John, directly?
He posts on Audio Asylum

 

[LynnOlson]

Part Two of the Positive Feedback Online article is out:
http://www.positive-feedback.com/Issue66/dsd.htm

Part One is here:
http://www.positive-feedback.com/Issue65/dac.htm

I came to the surprising conclusion in the second article that DSD is a variable-resolution system; over long periods of time (43 Hz or lower), it has 16 bits or more of resolution, but resolution decreases as the time interval gets shorter. Noise-shaping greatly improves converter performance at the A->D and D->A ends, but there's no way to wrap noise-shaping around the entire chain. (If the recording is made in 2001 and played back in 2013, there's no way to wrap digital feedback around the entire signal chain.)

The substantial presence of HF dither randomizes the error terms, in a way very similar to film grain limiting the ultimate resolution of film. Film grains are all black; there are no "gray" grains anywhere, and the base of the film is clear. What appears as gray to the eye is simply a random assortment of black grains that have a size that gives a visual impression of gray. DSD operates in the same way, with dither-noise at a high frequency acting like film grain. Unlike film, though, the minimum particle size of DSD is quantized, which is what limits the ultimate resolution of the system, regardless of noise-shaping.

Another key difference is the very high Nyquist frequency of DSD, which is approximately 1.4MHz. I say "approximately" because at that frequency the resolution is only 6 dB, or 1 bit. DXD, an intermediate PCM digital-processing medium sometimes used with DSD, has a Nyquist frequency of 176.4kHz, which is well above the response limit of studio microphones or playback loudspeakers. Although Gibbs ringing at the top edge of the audio band is undesirable, it won't be stimulated if the studio microphones have very little output above 50 kHz, and nothing at all above 100 kHz.

The Bruno Putzey interview makes it clear that multiple DSD -> DXD -> DSD passes are undesirable because of dither-noise noise buildup that eventually starts to clip the DSD system; Bruno's view is that DSD is best as a single-pass system that goes from a 2-track analog mastertape straight to the consumer, in the form of SACD or a DSD download, with no intermediate processing. (It should be mentioned that re-dithering is required any time a signal is taken in or out of native DSD format, so DSD -> DXD -> DSD entails another two stages of dither.)

DSD-Wide (2.8MHz/8-bit) is an interesting system, because it does not require noise-shaping, unlike DSD-Narrow (2.8MHz/1-bit). Although dither is still desirable (as it is in any digital system), it's not required for the system to operate, again, unlike DSD-Narrow. Although still awkward to level-adjust, equalize, or synthesize reverb, the conversion to the PCM domain is a lot more transparent, since high levels of dither are not required at each stage of conversion.