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Are all DACs the same - an investigation

Nessuno

Member
{needs explaining better please}

{needs explaining better please}

Consider the combination of a non-oversampling converter and the lack of any kind of reconstruction filter....

Even so, the plot shown suggests the presence of more and complex intermodulations than I would have expected when reproducing a solo 1kHz sine wave. Therefore, I conclude that something else has caused this problem to be rather worse than simple digital theory would imply.
Maybe the problem may lay in both the lacking of oversampling and reconstruction (a rather "squared" output with high energy spectral content in the region above 22.05kHz) and a following active analog stage (present in every DAC to adjust output signal level to match RCA or XLR connection standards), designed purposely with limited bandwidth to 20kHz and gentle slope, so still active but non linear in the region above 22,05 kHz, that in the mind of the designer would had act as anti-imaging of its own.

As a matter of fact every stage following the converter, with a low-pass type frequency response, could in theory act as an anti-image filter (even the speakers, if the sampling frequency is high enough!), but of course every sensibly designed DAC has a dedicated filter inside, to output a signal which is completely clear outside audio band. The reason is exactly to avoid interactions with following connected devices.

For this reason I asked Alan if the designer said that this strange behaviour was a design target or just a by-product of some other design choices. In other words, did he say: "yes, we know that our DAC produces spurious harmonics, this is how we want it to act" or rather "we designed the converter and the output stages for maximal "musicality", without thinking or knowing anything about those spurious, but we are content anyway".
 
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willem

Well-known member
So what is the consumer to do?

So what is the consumer to do?

So where are we now? We have one ultra expensive DAC assigned to the audiophile loony bin, in ways quite similar to the NUforce UDAC - 2: http://nwavguy.blogspot.nl/2011/02/nuforce-udac-2-drama.html So designing by ear may not be such a good idea. It is a result that is similar to the results from some ultra expensive amplifiers, that equally belong in the loony bin.

But what does this tell us about the potential of much cheaper scientifically designed DAC's? Do they also sound differently from each other? I found it interesting that the cheapest of the three that Alan tested, a pro audio Tascam/Teac unit, was best.

My conclusion from that, and from quite a bit of reading, is that well designed DAC's should all sound the same and need not cost a fortune. However, the bad news is that not all such DAC's are equally well designed (the mid price unit with the blue graphs was decent, but not particularly impressive). How, in the absense of proper scientific tests in the audio press, does the poor consumer avoid the mediocre ones? Avoid audiophile gear is a first step, but beyond that? Stick to major brands, or pro audio gear, even if cheap?
 

ssfas

Well-known member
Japanese manufacturing

Japanese manufacturing

It's a sad fact of life that there are more CNC machines than there is work, so small contract shops are trying to keep their machines running by doing whatever it takes.

Bar stock, cnc'd, centre pin fishing reels is a good example, there are dozens and dozens of small shops introducing these things because they are easy to make.
The problem is that your typical Japanese audio company is banging out 1000's of units a day using programmed welding and CNC machines that are probably produced by a fellow subsidiary in the same group.

I'm surprised 3D printing hasn't hit hi-fi yet. It's an incredibly flexible and efficient technology and 3D printed electronics is a reality. I have an interest in a company that 3D prints ladies underwear, so printing a DAC can't be much of an issue.
http://www.bloomberg.com/news/articles/2013-11-07/the-next-revolution-in-3-d-printing-disposable-panties
 

EricW

Active member
Understated NAD?

Understated NAD?

Let's take into consideration one of measurements for British DAC ....
Canadian, actually, since 1999 (http://en.wikipedia.org/wiki/NAD_Electronics), although I'm not sure what that means considering manufacturing is in Asia and the designer could have been from anywhere.

At least it seems to be an understated quality product, though, which I like to think is in keeping with the national character.
 

ssfas

Well-known member
Am I being conned?

Am I being conned?

The best I've got so far from my DAC supplier is from the chief moderator:

You mean subjective like the entire activity of listening to music? :)

Do not worry, we have no need to argue/discuss yet again objective v. subjective. I will note however I am comfortable knowing no one can hear the difference between 0.01% THD and 0.005% THD in a DAC. And fully cognizant of what happens when one becomes obsessed with specs over sound.

Manufactures have indeed become reticent in publishing specs since the THD wars of the 1970's. I suspect this is because enthusiasts have learned the pitfalls of relying on specs alone, and so much equipment now appears very similar when measured even though it does not sound the same. But there can be differences and I appreciate that Stereophile and others continue to measure.

...

As to your question, I have not personally seen such measurements from [our company]. [The boss] will likely be along soon and is in much better position to comment.


So is he saying:

1. AS's Option B is acceptable.
2. Tests results are meaningless
3. Listening is preferable
4. Our $6,000 DAC is pretty much the same as the next guy's?

I haven't got the $6,000 DAC, but I still feel conned.
 

acroyear

Active member
Firmware revisions and sound quality?

Firmware revisions and sound quality?

Let's take into consideration one of measurements for British DAC made by John Atkinson from Streophile some time ago:

http://www.stereophile.com/content/nad-m51-direct-digital-da-converter-measurements

Alan's measurement simply reveals we deal in this specific case, with technological, pardon me, lemon :).

ATB
The end of that review is interesting where a later firmware revision had people feeling the prior sound was better (more bass etc), a NAD representative later commented that the only change was a reduction in gain of 1dB (to give more headroom) saying that nothing should have effected frequency response....
 

pkwba

New member
Gadgetology and nominal upgrades (at best)

Gadgetology and nominal upgrades (at best)

So where are we now? We have one ultra expensive DAC assigned to the audiophile loony bin, in ways quite similar to the NUforce UDAC - 2: http://nwavguy.blogspot.nl/2011/02/nuforce-udac-2-drama.html So designing by ear may not be such a good idea. It is a result that is similar to the results from some ultra expensive amplifiers, that equally belong in the loony bin.

But what does this tell us about the potential of much cheaper scientifically designed DAC's? Do they also sound differently from each other? I found it interesting that the cheapest of the three that Alan tested, a pro audio Tascam/Teac unit, was best.

My conclusion from that, and from quite a bit of reading, is that well designed DAC's should all sound the same and need not cost a fortune. However, the bad news is that not all such DAC's are equally well designed (the mid price unit with the blue graphs was decent, but not particularly impressive). How, in the absense of proper scientific tests in the audio press, does the poor consumer avoid the mediocre ones? Avoid audiophile gear is a first step, but beyond that? Stick to major brands, or pro audio gear, even if cheap?
Do you remember the times when graphic equalizers were trendy in home hi-fi, more precise and elaborated - better. I bet that 99,99% of their home owners had not even basic idea how to use them properly :).

I think that separate DACs will exist on the hi-fi market for few years only until the audio guys get bored with new common gadget, then they will come back mostly to the integrated devices. Only small group of devoted audio-freaks will be cultivating more and more zany devices of this type. Note that many of older, very good but separate dacs are completely useless with the advent of new high dense audio formats.

The idea of "significant improving" sound from CDs by buying new separate dac is rather miserable in encounter with real life. Maybe if music lover used very simplified cd player he could hear some difference, but in case of common hi-fi enthusiast the sonic effect of "upgrade" is nominal if none.

ATB
 

ssfas

Well-known member
'The mouth is a yappin''

'The mouth is a yappin''

I seem to have got under the skin of the designer of my DAC. I gave him the "search for the truth speil" and here's what he said.

Yes, but most can't figure out and understand their own presuppositions and hence all following logic is based on sand and often worthless.

I think I understand a lot of what it takes and hence I built the [DAC], I chose each part based on the datasheets and tested my understanding with spice simulations. I'm gratified to see that doing the best I could from a theoretical perspective sounds the best and, for example, that I didn't have to do extensive listening for each part to pick it. This is in opposition to your points 1, 2 and 4. And, yes, the [DAC] doesn't measure as well in some traditional measurements as most other DACs: the obvious conclusion is that those things don't reflect what the ear/brain cares about – still I got there by understanding and the scientific method not voodoo. The difference is that I don't feel a need to justify my experiments and my conclusions to others, instead I used them to build a good sounding DAC.

If you'd like to see some of what I believe matters you can watch the videos at the [company] web site re the [DAC].

I warn you ahead of time that many reject out of hand some of my hypotheses, but I believe the proof is in the pudding.

Jitter can be measured, power supply firmness can be measured, linearity can be measured, EMI, RFI, etc. can be measured. One problem is that many don't believe these things matter as much as they do and another problem is that we don't have good ideas of how to measure what the ear/brain cares about for good sound.

I did the best I could in every dimension that I could attack and left the rest to software (which I'm pretty good at) so that I could continue working on the DAC after it was released.

And for that matter I have picked essentially every piece of my system based on what I consider to be solid principles based on the published info about them. Of course I listened as well, but if I didn't have an understanding of why a component should sound good I didn't waste time on that component and further I don't chase the best measurements, I chase the best design principles.
After one or two other responses, the designer added:

[QUOTE}Yep, if the feet ain't a tappin' who cares what the mouth is a yappin'[/QUOTE] - which pretty much sums it up.
 

tmokbel

Member
Disgraceful, and more confused consumers

Disgraceful, and more confused consumers

You are wrong on all counts, although admittedly I had the very same thoughts.

When presenting the above information to the manufacturer with the back-up graph as shown above, this was the response ...

  1. 'What do you know about DACs, you make speakers. We carefully checked the unit before we mailed it to you and it's performing exactly as it is designed to do. We double checked that in our test lab'
  2. 'This unit is an award winner'
  3. 'We sell lots of them and have a long waiting list'
  4. 'Yes, I agree, the distortion plots are 'unusual' but distortion is only one side of the story. What about musicality. I don't challenge your measurements at all, but go listen to music please'
  5. 'We have designed out the componentry that messes up the sound and that's why our product is so clearly musically superior'
  6. 'You are fixated on technical stuff. We are much more interested in the musicality'
  7. 'No one else has complained. And this gear has been through many of the golden ears in the industry, and they all love it'
  8. 'Look at this web site and see how digital audio sampling works, and note that we've gone back to the first principles, and simple chips and minimalist circuitry ...'
  9. 'No, I've never heard of or read D.E.L Shorter's seminal 1950s work on the audibility of harmonics. You say he was Dudley Harwood's predecessor at the BBC Research Dept. So what? That was a pre-digital time...'
  10. 'Look, you are talking rubbish. We know what we are doing. We're a successful company. You are not in this area of manufacturing. How can you know the blood, sweat and tears that we've distilled into this design over man years'
  11. 'Who the hell listens to pure tones anyway? And what is 'pure'? Nothing can be 100% pure can it'
  12. 'You are just trying to make life difficult for us. As I keep saying, the media and public love these, can't get enough of them. That's all the proof you need that we're right, the other makers are wrong and so are you'
I lost my cool I'm ashamed to admit because the above, esp. 2, 3, 7 and 12 are downright offensive. I like you, expected an entirely different apologetic response along the lines that a fully tested replacement would be with me overnight. As you can see, what I got was a robust defense of the unit in my hands.

So no, the unit is working as intended and presumably its replacement - which was not offered - would have been no different. It's due to design choices. Now, if you subscribe to philosophy B, then none of this is of any importance, I'd guess. If you subscribe to A, then this unit does not meet the basic criteria of a high fidelity component.

Tell me this: who do the media actually represent and does wholly subjective reviewing deliver the best value products to the public?
This is utterly disgraceful. Other than this DAC manufacturers downright rudeness to Alan whose perseverance to proper standards in engineering and measurement was shunned, it really does elaborate on the mockery the hifi industry has become. The sad part is, the they can get away with it because the consumer has become confused, will believe others if unsure and uninformed and have some kind of self fulling prophecy in their mind when they bring the product home that it is genuinely better because of all the XYZ nonsense they have been told.

What I can say, is that more than anywhere, the HUG has taught me to think logically and not accept anything less than the good advice that has been shown time and time again - advice that has 90% of the time frustrated and stunned dealers as well as manufacturers at audio shows with my questions of measurement and evidence of the claims they make.
 

A.S.

Administrator
Staff member
Demonstration of high-order harmonics

Demonstration of high-order harmonics

Taking the rich harmonic spectrum from the DAC I assessed, and reminding readers that it was the listening test on pure tones that first alarmed me, I have generated a pure 1kHz tone then added into in the 2, 3 .... 15th harmonic at approx. the same level as in the DAC spectral plot shown in post #74. We can now hear what I heard.

First you will hear 10 seconds of the pure tone. Use this first tone to adjust your (PC) speakers so that they do not distort - you'll hear as you adjust the volume that beyond a certain setting, the tone becomes dirty due to your sound card/plastic speakers etc. distorting. Leave the volume set below that critical threshold. Then follows a short silence, and then the synthesised DAC output.

You'll probably find that as you move your head about that the buzzing sound, due to the presence of the harmonics, becomes more or less audible.

1kHz pure and DAC output

If I slow down that file to half speed, it saves me ten minutes regenerating all the harmonics, one by one. So here is the file pitch-shifted down to 500Hz, with the correct relationship with the harmonics.

500Hz pure and DAC output

Whether you think this pure-tone distortion is a significant audible issue or not depends entirely on your perspective. Played over a proper hifi system where these is the possibility to increase the loudness beyond that of a pc speaker, the effect is significantly more obvious. Do you subscribe to philosophy A or B? To my ears, this harmonic distortion sounds like, and measures like a defective, rubbing, buzzing bass/midrange unit.

We must also consider this. If that degree of distortion is considered benign or unconcerning, then it sets an threshold of 'goodness' beyond which high fidelity equipment yields rapidly diminishing performance returns. We would be back full circle to the position of audio excellence in the mid 1960s. If distortion of, say, a percent or so is acceptable, then there is not the lightest justifiable argument for chasing specifications such as 0.001% distortion, nor a noise floor quieter than bog standard CD - or even LP for that matter.
 

Nessuno

Member
Specifications and excellence

Specifications and excellence

The manufacturer's reply:
While I enjoy that enthusiasts run such tests and are actively engaged, I always review these with a great deal of skepticism. It is much more difficult to properly measure audio equipment than many understand. This is one reason the results vary so greatly from one enthusiast's findings to another. For that matter, the results vary between professional knowledgeable reviewers as well as manufacturers.

The same issue exists with enthusiasts attempting to judge the sound and resolution of recordings by reviewing spectra. This is not to say measurements are not valuable. They are and I love specs and tests. But I also do not listen with my eyes.
In general terms this is a perfectly understandable position and in my view the right one to keep: as a matter of fact the eyes don't listen!

Given in correctly conducted measurements some minimal standards are honoured (there is space to fill here, I think this could be acceptable: flat FR in audio band, S/R ratio better than 90dB, THD at 1kHz below 0,01% and something more could be added for specific devices), I think it's a conceptual error to start from a graph or a measure and on this base alone question the ability of a device to reproduce music with fidelity to the ear. This is exactly the pseudo-science trap a lot of audiophiles are caught in.

What happened with the DAC case at hand is the exact contrary: a device sounded bad, so evidently bad that not even a DBT test was necessary to assess the presence of a real listening difference (*) then a measure shown where the problem was. The measure shown a large deviation from acceptable standards, but extending this case to question a distortion of 0,001% against 0,002% or a fraction dB rolloff from 17kHz on, without even trying to test if those figures mean something to the ear, could be misleading.

(*) of course Alan's ear is a very trained one and the measurement shows he was right (a spurious signal 48 dB below a single tone is surely audible), but in the most general case, a blind test must be required.
 

ssfas

Well-known member
Future proofing?

Future proofing?

I think that separate DACs will exist on the hi-fi market for few years only until the audio guys get bored with new common gadget, then they will come back mostly to the integrated devices. Only small group of devoted audio-freaks will be cultivating more and more zany devices of this type. Note that many of older, very good but separate dacs are completely useless with the advent of new high dense audio formats.
You are no doubt correct. Early DACs were also sold on their offering multiple and various digital inputs. These are now standard on the cheapest devices. Personally, I don't think high density formats have much of a future either.
 

grandwazoo

New member
Unacceptable

Unacceptable

Taking the rich harmonic spectrum from the DAC I assessed, and reminding readers that it was the listening test on pure tones that first alarmed me, I have generated a pure 1kHz tone then added into in the 2, 3 .... 15th harmonic at approx. the same level as in the DAC spectral plot shown in post #74. We can now hear what I heard.

First you will hear 10 seconds of the pure tone. Use this first tone to adjust your (PC) speakers so that they do not distort - you'll hear as you adjust the volume that beyond a certain setting, the tone becomes dirty due to your sound card/plastic speakers etc. distorting. Leave the volume set below that critical threshold. Then follows a short silence, and then the synthesised DAC output.

You'll probably find that as you move your head about that the buzzing sound, due to the presence of the harmonics, becomes more or less audible.

1kHz pure and DAC output

If I slow down that file to half speed, it saves me ten minutes regenerating all the harmonics, one by one. So here is the file pitch-shifted down to 500Hz, with the correct relationship with the harmonics.

500Hz pure and DAC output

Whether you think this pure-tone distortion is a significant audible issue or not depends entirely on your perspective. Played over a proper hifi system where these is the possibility to increase the loudness beyond that of a pc speaker, the effect is significantly more obvious. Do you subscribe to philosophy A or B? To my ears, this harmonic distortion sounds like, and measures like a defective, rubbing, buzzing bass/midrange unit.

We must also consider this. If that degree of distortion is considered benign or unconcerning, then it sets an threshold of 'goodness' beyond which high fidelity equipment yields rapidly diminishing performance returns. We would be back full circle to the position of audio excellence in the mid 1960s. If distortion of, say, a percent or so is acceptable, then there is not the lightest justifiable argument for chasing specifications such as 0.001% distortion, nor a noise floor quieter than bog standard CD - or even LP for that matter.
I agree that buzzing is distracting to me even over my PC speakers, I don't think I could tolerate a home hifi with that much distortion. I still subscribe to Philosophy A which to me yields the highest levels of fidelity.
 

acroyear

Active member
The practicality of vintage audio gear

The practicality of vintage audio gear

subjective and naive, but this was before I signed up to the HUG.
We live and learn, and I feel your frustration.

I traded in a barely used amp recently simply because despite its extra power and lower sensitivity compared to its predecessor, ultimately it still could overload early, it still had no subsonic filter or tone controls, any way to control gain, but I had convinced myself that its valves (a hybrid amp) were giving me an amazing sound, and I believed it, switching out my old amp with modest volume CD's I realized I couldn't tell the difference, those new sounds could be heard with my old amp, I was now just aware of them.... in its defense the new amp was no doubt competent, it was built like a tank and not too expensive, (I was going to utilize the extra power in the TV room but alas the amp was just too big to fit into the cabinet) though it did have some issue with buzz/hum that the designer said was matching valves and class D, I digress.

HUG has delivered me from the assumption that more $ is necessarily better, that a minimal fixed sensitivity amp is simply NOT a good proposition for CD, what use is an amp that lets through subsonic signals from a warped record, every sensible audio engineer knows that is just crazy, why have 5 inch drivers trying their hardest to make a 5Hz signal when you are trying to crank your music to 90dB....

I was in an audio shop a few weeks ago where there was lots of vintage gear, some had gain knobs, most had subsonic filters, all had tone controls, some with variable slopes and settings, it was all very practical!
 

Batears

New member
3D printing in the lab

3D printing in the lab

The problem is that your typical Japanese audio company is banging out 1000's of units a day using programmed welding and CNC machines that are probably produced by a fellow subsidiary in the same group.

I'm surprised 3D printing hasn't hit hi-fi yet. It's an incredibly flexible and efficient technology and 3D printed electronics is a reality. I have an interest in a company that 3D prints ladies underwear, so printing a DAC can't be much of an issue.
http://www.bloomberg.com/news/articles/2013-11-07/the-next-revolution-in-3-d-printing-disposable-panties
Those printers shown in the the above link are very small, look at the red tool boxes beside each machine and check the actual cubic work area inside the machine.
I have just finished building a small printer from scratch, rather than a kit, and I'm not convinced that it is possible produce the article mentioned in 3 seconds

Printers no matter how lightly built have inertia and whether the print head or the table moves, they both have weight, and to zoom around at the speeds suggested in the link takes some believing. I would have liked to have seen a video as well as the story of the above in action.

There is not much choice in the plastic filament used, usually a soft thermoplastic with very little strength. Intricate parts that can be produced on 3d printers are amazing but they take time so printers are really only good for development parts.
 

pkwba

New member
Respected NAD

Respected NAD

Canadian, actually, since 1999 (http://en.wikipedia.org/wiki/NAD_Electronics), although I'm not sure what that means considering manufacturing is in Asia and the designer could have been from anywhere.

At least it seems to be an understated quality product, though, which I like to think is in keeping with the national character.

I replayed for some time all my records (cd, dvd, dvd-a, sacd) with NAD M55 multiformat player - very good and robust device with superb sound. I have changed it to the newer (Oppo 105) only because of new BD format. I had no idea they moved headquarters from UK to Canada. They owed their good quality in the beginnings of a company due to production located in Taiwan. Methink now they have their manufacturing / assembly spread all over the world.

NAD is still very popular in Europe offering hi-fi from medium to high-end devices. Respected brand.

ATB
 

mhennessy

Member
The obvious inconsistency - forgotton basic design rules

The obvious inconsistency - forgotton basic design rules

Some food for thought:

It seems that some audiophiles are OK with, or perhaps even actively enjoy, the gross distortion reported here.

Yet, almost universally, audiophiles refuse to accept the notion of lossy data-rate reduction.

But a simple difference-test will demonstrate that unless you use exceptionally low data-rates for the codec in question, the impact on the audio will be utterly trivial in comparison to the clipping reported here and on NaAvGuy's website.

So is this not yet another demonstration of the simple fact that some people don't listen with their ears ;)

I've lost count of the number of DACs I've measured over the years. Dozens, maybe 100s. I have *never* encountered one that clips - not even when presented with +dBFS signals. But based on recent reports, it would appear that some people have forgotten - or abandoned - the most elementary rules of audio design.

Very sad, but perhaps not all that surprising.
 

HUG-1

Moderator
Fixated on one aspect of design?

Fixated on one aspect of design?

... It seems that some audiophiles are OK with, or perhaps even actively enjoy, the gross distortion reported here. Yet, almost universally, audiophiles refuse to accept the notion of lossy data-rate reduction....But based on recent reports, it would appear that some people have forgotten - or abandoned - the most elementary rules of audio design.

Very sad, but perhaps not all that surprising.
As we understand it, the reason the featured DAC performs as it does is because the designer has "removed the output filter". He blames that part of the circuit for "killing the sound".
 

pkwba

New member
HQ formats and their future.

HQ formats and their future.

You are no doubt correct. Early DACs were also sold on their offering multiple and various digital inputs. These are now standard on the cheapest devices. Personally, I don't think high density formats have much of a future either.
I am not well-versed as for pop music in general, but in case of classical music HD formats are gradually overcoming internet audio market quite successfully and it is not polished coal but new recordings offered by multitudinous and still growing number of renowned classical labels.

Recording / mixing / mastering classical music in HD formats became technical standard practically decade ago. The only issue is one must control carefully the state of one's pocket :).

ATB
 
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