Thoughts on a bunch of DACs (and why delta-sigma kinda sucks, just to get you to think about stuff)
Jul 5, 2018 at 10:00 PM Post #6,421 of 6,500
Right (IM here being two-tone stimulus I take it).



This is an interesting avenue of study. The filters in S-D DACs are in general built down to the lowest silicon area possible, which means adopting a half-band filter for the first stage upsampling (1X->2X). Half band filters are a compromise to save on MACs - half the coefficients are zero. The downside is the FR violates Nyquist because instead of the Nyquist frequency being firmly in the stop band, its in the transition band and only single digit dB down (I forget if that digit is 3 or 6)

Summing up so far then we look to be in broad agreement that today's measurements aren't telling the whole story about a DAC's performance as we have the 'Sabre brightness' not being shown up in any measurements so far. I would add to the 'brightness' issue the biggest thing lacking for me in an ES9023 and that's subjective dynamics. I also haven't much clue what measurement is needed to quantify subjective dynamics but my first stab at it would be noise modulation.
we're all similar people presented with the same options. we feel something and get some idea as to why. then from time to time, measurements seem to conflict with those impressions and ideas. and that's where we're not so similar anymore:
-when I'm presented with objective data contradicting my ideas and memories, if I can test my idea with some control, I'll do it and see what happens. when I can't, I consider the conflict to be big enough of a problem not to decide that my feelings and ideas are conclusive. and if I absolutely have to pick a side, I'll side with the objective data(but that's really something I'd rather avoid).
-based on the last few posts, it's pretty obvious that not only you take your feelings and ideas very seriously, but when they conflict with measurements, you decide to suspect the measurements of being flawed or incomplete instead of second guessing yourself and the quality of your experiences.
you bring up some fairly reasonable questions about measurements. we obviously don't get enough specs by default. and with the natural tendency from manufacturers to "forget" the variables showing bad specs for their gears, having apparently good specs are even less of a proof that we'll get transparency. but focusing on that alone is pure fallacy. we obviously also have to deal with our testing conditions and all the possible issues we can just call "human error". from the sighted anecdotal experiences, the accuracy of our memories, the quality of interpretation, jumping to conclusion, etc. all very real very relevant concerns. trying to find which set of measurements is effectively presenting what we feel, that should obviously come after making sure that what we feel was induced by sound in the first place. something the average audiophile is not going to do, because of ignorance, laziness. or the usual idea that preconceptions, placebo, logical fallacy, etc, all somehow belong in the box labelled "it only happens to others".

I've followed discussions about the sound of delta sigma vs R2R, the specific sound of some chipsets and related stuff. I'm personally very curious about this, I've tried to test my fair share of gears and conditions, but right now I have no confidence claiming that anything is real or more than circumstantial. I've very clearly failed to pass blind tests using DACs with different chipsets. I can blame my low listening skills and my ears not growing younger, but whatever the reason, those DACs were still good enough to fool me.
I also have been able on rare occasions, to identify some DACs despite them having the same chipset.
the usual idea that R2R will have less linearity and more aliasing or treble roll off, while delta sigma has more noise, even such generalities based on the designs can be contested if we go pick the right DACs. some R2R stuff have impressive linearity, some delta sigma have impressive SNR.
so all in all, I'm confident that at a statistical level we can find patterns and correlations, but who has gone through enough gears in a rigorous enough way to call his results statistically significant? I sure didn't.
 
Jul 6, 2018 at 9:27 AM Post #6,422 of 6,500
I can think of a few reasons....

1) Many DACs, especially more esoteric designs, employ additional upsampling in addition to the oversampling inside the DAC. In fact, many tout it as a feature.... Note how many DACs "upsample to 384k" or "upsample to DSD" using some proprietary firmware or FPGA before sending the data to the DAC, usually claiming some sort of audible improvement as a result...and some customers believe those claims (I'm not saying either way). However, you could take it as a simple statement of fact - that they do NOT do any of that extra sample manipulation.

2) Being more cynical, you might suggest that enough people seem to believe that "not oversampling" is a virtue that they feel they'll sell a few more DACs by encouraging the misunderstanding. (Non-oversampling DACs share several drawbacks, which tend to make their technical performance look relatively poor... competing against them makes the Antelope DAC look better by comparison.)

Thank you for the detailed explanation! For the record, this is how the sampling was described in the 6moons review: "the Gold always processes incoming data at its native resolution without internal upsampling. What goes in is what comes out." However, as you note, there is upsampling in the DAC chip itself - in this case, a dual 1792A chips, which according to their spec pages, indeed upsample... so I'm not sure why they are making this claim. http://www.6moons.com/audioreviews/antelope2/1.html
 
Jul 6, 2018 at 10:11 AM Post #6,423 of 6,500
I'm not an expert on the math of designing filters, but I'm pretty sure that, while the overall response is very important, the design of the individual stages doesn't count for much. Therefore, if they're using several stages, it would only be the aggregate response of all of them that matters. Therefore, the design of a single stage could seem poor, but a cascade of several such "poor stages" could actually produce an excellent aggregate response. of course, it also may not. Most DAC chips offer a variety of oversampling options to the designer, many of which may be better or worse in various different ways... and, presumably, some of the choices and combinations simply don't perform very well in important ways.

Sabre DACs are also interesting in other ways. For example, you may be familiar with ASRCs (asynchronous sample rate converter). Many DACs incorporate an ASRC to eliminate jitter (I believe Benchmark was the first). To horribly oversimplify how they work, an ASRC converts the incoming digital audio data to a new sample rate. In the process, the data is re-clocked to a new local clock, so any jitter associated with the incoming clock is eliminated, or drastically reduced. Some people have an aesthetic objection to the fact that "every single sample of the original data is discarded and replaced with new interpolated data". However, from a technical perspective, all that counts is that the analog data that comes out the end is improved because the effects of the incoming jitter are removed. In most DACs that have this feature, it is implemented using a dedicated "ASRC chip" - often an Analog Devices AD1896, a TI SRC 1492, or the equivalent from Cirrus Logic. Sabre DACs have a similar jitter reduction method built in.... it actually introduces corrections into the data as part of the upsampling process. Again, horribly oversimplified, jitter causes problems because you end up with the correct value being submitted to the converter stage at a slightly wrong time, resulting in a wrong output value. A standard ASRC addresses this by correcting the timing. Sabre's method, according to their conceptual description, essentially calculates the error, then adjusts the value of the data sample itself to "compensate" for the error introduced by the faulty timing. I have no particular opinion about which method is "better", but both incorporate complex DSP calculations to make corrections to compensate for errors in the data - so both offer the opportunity for the "corrections" to introduce changes that might be audible...

Some DACs that use a separate ASRC allow you to bypass it so to evaluate any audible changes it might introduce for yourself. As usual, when it comes to complex digital filters, the actual changes such devices cause tend to be complex and somewhat difficult to describe. For example, several of our Emotiva DACs have included an ASRC, with the option to disable it, and it most definitely produces a subtle alteration of the sound. If you start out with a source that is extremely high in jitter, then the difference is usually what I would consider to be a small but distinct improvement. However, if you start out with a signal that has relatively low jitter, there is still a slight audible difference in sound - but it becomes more difficult to describe, or to identify as "better or worse". As a broad generality, many digital filters produce subtle differences which can be measured using various metrics. Often, however, it becomes a matter of personal taste which one is "better" - and whether a given person notices one or the other at all.

I should also note that there's a middle ground. Most commercial DAC chips offer the designer the option of using the internal filters, often a choice of several different ones, or of adding their own external filter altogether... and many DAC vendors do just that. However, actually designing digital filters is very complex. Many DAC vendors have their own filter designs which they insist are better than the included ones. Interestingly, if you read a lot of reviews in the sorts of magazines that do serious math, you sometimes find that a certain DAC has "a unique sound" because the filters it incorporates are simply badly designed, or designed to perform very well in certain specific ways at the expense of other important parameters, and the designs of one or two of them have simply been found to be based on faulty math. Companies like Analog Devices and AKM spend a lot of money optimizing the performance of their products; some of us think they know what they're doing, and see little reason to "reinvent the wheel" when the options they provide work really well. (In terms of deliberately "boutique sound", many non-oversampling DACs incorporate gentle roll off filters, which have a very clean ringing characteristic, but also a very slow high frequency roll off. You end up with a DAC that has very little ringing, but a frequency response that is -3 dB at 20 kHz with a 44k input signal. As a result, plucked strings sound clean and sharp, but it becomes difficult to tell if the "smooth sound" you hear is really due to the lack of ringing - or simply to the rolled off high end. And, yes, if your speakers had a rising high end, the two flaws might cancel out perfectly... producing some of that legendary "synergy" people talk about. )

Right (IM here being two-tone stimulus I take it).

This is an interesting avenue of study. The filters in S-D DACs are in general built down to the lowest silicon area possible, which means adopting a half-band filter for the first stage upsampling (1X->2X). Half band filters are a compromise to save on MACs - half the coefficients are zero. The downside is the FR violates Nyquist because instead of the Nyquist frequency being firmly in the stop band, its in the transition band and only single digit dB down (I forget if that digit is 3 or 6)

Summing up so far then we look to be in broad agreement that today's measurements aren't telling the whole story about a DAC's performance as we have the 'Sabre brightness' not being shown up in any measurements so far. I would add to the 'brightness' issue the biggest thing lacking for me in an ES9023 and that's subjective dynamics. I also haven't much clue what measurement is needed to quantify subjective dynamics but my first stab at it would be noise modulation.
 
Aug 3, 2021 at 7:26 PM Post #6,424 of 6,500
$500.00 for a 24/48 WOW:confused:
And people tell me my Hegel is overpriced.

As if that's the most important characteristic LOL.

Most of material for many people is red book anyway, so anything beyond that is a pleasant, but insignificant feature for a DAC.
 
Aug 3, 2021 at 7:52 PM Post #6,425 of 6,500
Hey Purrin if you are around what do you think of Esoteric's lineup and PCM63 DACs? I correct myself, they mostly use PCM1704 chips. I saw an Esoteric D-3 and I was wondering if you have heard this one before. It uses 8x AD1862N chips

I am getting Esoteric D-30 with 8 PCM63 chips soon.
 
Aug 4, 2021 at 9:31 AM Post #6,426 of 6,500
Comment on a occasion of refreshing dead thread. There is a new Audio GD DAC powered 8x_PCM1704 HE7MK2 with regenerative power supply released just few days ago. It is a major redesign of the analogue board since the last +8 years, plus the entirely new digital section delivered from other Audio GD DACs MK2 version. It means asynchronous USB transfers through a galvanic isolator synchronised with a fixed frequency internal oscilators, optimised clocking design and more.
 
Aug 5, 2021 at 7:26 PM Post #6,427 of 6,500
Comment on a occasion of refreshing dead thread. There is a new Audio GD DAC powered 8x_PCM1704 HE7MK2 with regenerative power supply released just few days ago. It is a major redesign of the analogue board since the last +8 years, plus the entirely new digital section delivered from other Audio GD DACs MK2 version. It means asynchronous USB transfers through a galvanic isolator synchronised with a fixed frequency internal oscilators, optimised clocking design and more.

Do they make anything on PCM63 or PCM65?
 
Aug 5, 2021 at 7:59 PM Post #6,428 of 6,500
Do they make anything on PCM63 or PCM65?
Not. PCM63 is not selling for number of years. What you see on Aliexpress is coming from recycling facilities and beware of fake chips...

I picked up a Rotel CD player RCD-971 circa 2002 and it was already announcement ending production. PCM1704 is still available from reputable sources, but it could be the last batch, I think.
 
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Aug 5, 2021 at 11:54 PM Post #6,429 of 6,500
Not. PCM63 is not selling for number of years. What you see on Aliexpress is coming from recycling facilities and beware of fake chips...

I picked up a Rotel CD player RCD-971 circa 2002 and it was already announcement ending production. PCM1704 is still available from reputable sources, but it could be the last batch, I think.

Do you know btw which DACs used PCM65? I have read it was the best version of the chip, but rare and expensive one.
 
Aug 6, 2021 at 8:17 AM Post #6,430 of 6,500
Do you know btw which DACs used PCM65? I have read it was the best version of the chip, but rare and expensive one.
A quick google search didn't mention any standalone DACs but did mention a Pioneer CD player (Pioneer Elite PD 91)
 
Aug 6, 2021 at 8:19 AM Post #6,431 of 6,500
Correct. Pioneer PD-91 and few more: Pioneer PD-3000 and Stax CDP Quatttro II comes to my mind.

DAC chip is only a part of the story. There is implementation of digital filters (if any), clock synchronisation, voltage regulation, design layout (i.e. ground distribution) and of course power supply and the analog section. A DAC I linked-in has regenerative power supply, very complex conversion technique working at a low frequency.

Some of design internals are not disclosed in datasheet, it is discovered during years of experience. By example in the PCM1704 the most important clock from jitter perspective is not a word clock as usual. Those who try to optimise word clock jitter do not get the best results.
 
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Aug 6, 2021 at 5:20 PM Post #6,432 of 6,500
Correct. Pioneer PD-91 and few more: Pioneer PD-3000 and Stax CDP Quatttro II comes to my mind.

DAC chip is only a part of the story. There is implementation of digital filters (if any), clock synchronisation, voltage regulation, design layout (i.e. ground distribution) and of course power supply and the analog section. A DAC I linked-in has regenerative power supply, very complex conversion technique working at a low frequency.

Some of design internals are not disclosed in datasheet, it is discovered during years of experience. By example in the PCM1704 the most important clock from jitter perspective is not a word clock as usual. Those who try to optimise word clock jitter do not get the best results.

Stax CDP Quatttro II – oh wow, never knew such thing even existed. Thanks.
 
Aug 6, 2021 at 8:07 PM Post #6,433 of 6,500
Correct. Pioneer PD-91 and few more: Pioneer PD-3000 and Stax CDP Quatttro II comes to my mind.

DAC chip is only a part of the story. There is implementation of digital filters (if any), clock synchronisation, voltage regulation, design layout (i.e. ground distribution) and of course power supply and the analog section. A DAC I linked-in has regenerative power supply, very complex conversion technique working at a low frequency.

Some of design internals are not disclosed in datasheet, it is discovered during years of experience. By example in the PCM1704 the most important clock from jitter perspective is not a word clock as usual. Those who try to optimise word clock jitter do not get the best results.
Very good points, but I might go a step further and say that any reasonable DAC has a clock that performs well beyond the capability of any human ear. The whole magic clock tweaking stuff people do is absolutely measureable, but not resulting in audible difference. Not a chance people can hear jitter at all, let alone when music is playing.
 
Aug 6, 2021 at 9:02 PM Post #6,434 of 6,500
Very good points, but I might go a step further and say that any reasonable DAC has a clock that performs well beyond the capability of any human ear. The whole magic clock tweaking stuff people do is absolutely measureable, but not resulting in audible difference. Not a chance people can hear jitter at all, let alone when music is playing.
Clock quality do matter. It may be not noticed with supermarket grade $100 devices with fake opamps like my Topping D30, but it will be noticed immediately with better DACs/amps and speakers . Once transparency of the system reaches a certain level, it matters even more. HE-7 MK2 comes with Accusilicon 318B femtosecond clocks, but specialised clock devices have jitter a magnitude lower. Connecting such device removes any sign of digital glare. Look in the high-end section, what people have to say. PM me and I can direct you directly to the members who have such setup.

Measurements? Frequently we do measure wrong things, like ground loops in the measuring gear. Example: Total DAC Six tests on ASR.
 
Aug 6, 2021 at 10:09 PM Post #6,435 of 6,500
Very good points, but I might go a step further and say that any reasonable DAC has a clock that performs well beyond the capability of any human ear. The whole magic clock tweaking stuff people do is absolutely measureable, but not resulting in audible difference. Not a chance people can hear jitter at all, let alone when music is playing.
I agree that for some, 'better' clocks may not be discernible, but for others it is easily discernible.
I for one heard a marked improvement when I added an external reclocking board to my PSA PWD MkII.
The Bridge only did one thing and that was to reclock the incoming USB signal.
It made an immediate improvement everywhere.

JJ
 

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