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Shouldn't every DAC by design sound pretty much identical?

Discussion in 'DACs' started by Cosmo-D, Jul 31, 2018.

  1. Cosmo-D

    Cosmo-D AK Subscriber Subscriber

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    So as I understand it digital audio is basically the original waveform, but viewed through the lens of PCM, Nyquist theorem, whatever. Given the same sampling rate, encoding method, et cetera a particular analog sound should always produce the same bits provided the volume and what-have-you is identical. That is to say there is a direct relationship between bits and sound they are supposed to store. Shouldn't every DAC therefore produce pretty much the same pattern of oscillating voltages given the same input? Isn't that what they are supposed to do? Obviously there is going to be a little variance in the form of noise and error. If two DACs produce markedly different output given the same input of bits is one or more of them not broken or flawed by design?

    If you consider the purpose of the device, would it not make sense for them to all sound pretty much the same? I feel like DACs that sound markedly different either have some kind of messed up implementation (like Audio NOS DACs with tubes in them) or some designer has intentionally made them to sound different in order to distinguish their product. Digital audio is supposed to be transmissible, and have the ability to be replicated infinitely. The arrangement of bits is meant to encode specific wave forms. A DAC should be able to render these. There isn't room for interpretation. There is really only one correct answer. So if a DAC is doing its job it should produce the same waves as encoded on the disc with an inaudible amount of noise/error. If a DAC has a particular "sound" then it really isn't doing its job properly, is it?
     
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  2. Retrovert

    Retrovert AK Subscriber Subscriber

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    Your question is a good one. The issue, however, is far, far more complicated than you describe, and books and technical papers have been written on the subject.

    Here is a very short explanation which I've simplified.

    The conversion process turns 1's and 0's back into an analog signal by converting digital values into voltages, some of which can be very small. Different DACs create those voltages in different ways, and the approximations inherently have, of necessity by way of the designs, different types of errors and introduce different kinds of artifacts. The reconstituted signal differs from the original in different ways depending upon the means whereby the DAC generates these voltages. The conversion process, furthermore, can itself create artifacts which must be filtered out. Those filters themselves add errors and artifacts. The size and cost of the DAC greatly varies, with greater accuracy requiring a physically larger and more expensive device.

    Different DAC technology has vastly different accuracy and wildly different costs, which is why the quality of the DAC in an inexpensive portable MP3 player or wireless headphones, or even a phone for that matter, will be very different than the quality in a stand-alone DAC for HiFi purposes. Audio people can throw money and circuit area at this problem, but phone designers and portable audio designers cannot.

    I suggest you do a search online for the DAC papers and books written by Analog Devices staff. Such writing is world class, and properly explains the considerable issues involved. Texas Instruments and National Semiconductor also produced excellent papers. The Burr Brown papers and books tend to be more theoretical and therefore significantly more difficult to understand. This is not to disparage other authors, just that the works I cited are readily accessible on the internet at no cost and will explain the basic issues involved.

    When I say this I'm not trying to dismiss your question, which, again, is a very good one. I'm trying to say the issue is very complicated and you'll need to spend a few hours, if not days, reading about how it works to understand the tradeoffs being made. The difference is not poor implementation or deliberate errors, but trying to solve a very difficult problem with fluid constraints such as board area, power consumption, component cost, and consumer price points.
     
  3. Poinzy

    Poinzy Super Member

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    DAC's have improved with time. Newer ones produce less distortion than the ones produced 30 or 35 years ago. That's what amuses me about people looking for "vintage" CD players: they think they're making a step up in sound over the newer devices because they think Swiss watchmakers assembled the old DAC's or something.

    Top-of-the-line NAD CD players sound better than other new, cheaper players because NAD use better-performing DAC's. Anyway, there are plenty of reasons to expect differences in performance/sound between DAC's.
     
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  4. sKiZo

    sKiZo Hates received: 8642 Subscriber

    All about chipsets and proprietary firmware. A lot of gear uses custom algorithms and faster processors to convert the incoming stream that can affect accuracy and buffer times, both of which can really improve sound if implemented correctly.

    It's not all about bitrate either. I much prefer the USB chain on mine even if it tops out at half the rating of the S/PDIF section. Just sounds better to my ears.
     
  5. Retrovert

    Retrovert AK Subscriber Subscriber

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    That is not necessarily true.

    Many current consumer items use inexpensive DACs or ones suffering from ringing in the upper part of the passband. Some of the DACs first used in consumer equipment were of high quality, and very expensive, because it was the only way to perform the conversion. Inexpensive chipsets are now available and lower-cost equipment using these may not sound as good.

    So an older CD player may have better build quality and better DACs.

    No blanket statement exists as per age, given that the sound quality really depends on design and the transfer price when new.
     
  6. E-Stat

    E-Stat AK Subscriber Subscriber

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    And don't forget the "A" part - the analog stage. I happen to find this part responsible for more of the differences you hear between various DACs. It is essentially a preamp line stage.

    Inexpensive ones use low current, noisy switch mode power supplies and low end op amps. The best use RFI filtered linear power supplies with R-core transformers feeding lots of energy storage and discrete output circuits that are fully balanced. There are considerable audible differences between $200 and $5000 DACs.

    I concur with Retrovert that newer isn't always better. I'll take an older, high quality unit over a budget driven new one any day.
     

     

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  7. Retrovert

    Retrovert AK Subscriber Subscriber

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    Right. Any ripple in the ground plane gets coupled into the analog stage. The noise from an SMPS gets into everything.

    Most consumer devices are purchased on price and brand as a fashion accoutrement. Nothing to do with quality.

    I don't know that it is necessary to spend very much on a good DAC, the Objective DAC (aka ODAC) by NWAvGuy will run you a few hundred bucks in a case. Far better than what you'd pay ten times for. Mostly because the engineering work and tooling was done and gifted to the community. Same for the O2 headphone amplifier. Again, no fancy brand name so you save a bunch of money.
     
  8. Cosmo-D

    Cosmo-D AK Subscriber Subscriber

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    Interesting. I am not well-versed at all on digital audio. I don't have much of an educational background in science or math (I got like a 65 in first-year linear algebra). My cheap-o Harmon/Kardon HD200 circa 1989 doesn't sound deficient at all to me when playing CDs. The drawer mechanism is kind of going (I will need to get a new CD player someday) so I tried using a cheap Sony DVD player for a bit and it worked fine as well. I expected some difference given that they are two consumer-level devices produced many years apart, but CDs still sounded like CDs. It wasn't as pronounced a difference as say changing the cartridge on my turntable. I don't have kit to do level-matched A/B-ing between devices, so I can only really speculate as to the differences.

    I am not really up on how these things work exactly. I am aware that DACs fall into one of two broad categories: multi-bit and delta-sigma. From what I've gathered multi-bit DACs would seem more prone to errors because they employ banks of resistors and the tolerances for resistors are only so good.


    Based on this review plus the measurements: https://audiosciencereview.com/foru...iew-and-measurements-of-topping-d50-dac.2403/ this Topping D50 DAC would appear to be the bees knees. Do you have any thoughts on it?

    I'll look into those paper when I get the chance.
     
  9. sKiZo

    sKiZo Hates received: 8642 Subscriber

    Haven't been disappointed with my Maverick TubeMagic here. Performs well above it's price point.
     
  10. Djcoolray

    Djcoolray Addicted Member

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    A rocks throw from JBLM !!!!
  11. E-Stat

    E-Stat AK Subscriber Subscriber

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    And with sockets for the op amps, it lends itself to upgrading to FET modules supplied from companies like Burson Audio.

    My Music Hall DAC 25.3 is much the better losing the OPA op amps in favor of their V5 FETs.
     

     

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  12. Retrovert

    Retrovert AK Subscriber Subscriber

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    You don't need a technical background to understand the limitations. Many of the writeups will give you a layperson's view, showing block diagrams of where the inaccuracies and errors arise. The Analog Devices background papers should be comprehensible.

    Many times the older CD and DVD players are of better quality. More steel, less plastic. I have thrown away a number of recent DVD players for trivial failures in plastic parts, while the older CD players are just fine. These older units do not, of course, play DVDs or MP3 CDs, which limits the utility.

    Plus a few types you left out, and the oversampling vs. non-oversampling issues.

    Banks of resistors is why laser trimming was used with thick-film networks, back in the day. Today's R2R ladders often use many precision resistors placed in parallel, as this reduces the errors.

    I don't know that product.

    I suggest you read about the Objective DAC. A lot of very fancy engineering went into it, and, as I noted, you're not paying someone's R&D or marketing costs.
     
  13. cpt_paranoia

    cpt_paranoia Well-Known Member

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    As mentioned by others, besides the actual DAC chip, the other factors determining the quality of an 'ensemble DAC; device (as opposed to the chip) are analogue output filtering & buffering, power supplies & decoupling, clocking, and PCB layout (to prevent coupling of noise between digital & analogue sections). In no particular order...

    Engineering is about compromise; it depends what we're compromising on. Mostly price. Price determines how much care you can take with all those aspects of the ensemble DAC.
     
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  14. Retrovert

    Retrovert AK Subscriber Subscriber

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    All very true. Noise is the enemy of low-level analog signals, and it takes real engineering work to minimize it. That's what NWAvGuy did which was so impressive. He put five grand worth of engineering into a very nice three hundred dollar box.

    Price is a funny thing. Much of price is positioning in a premium level for branding. Awful headphones sell for a lot of money because of a fancy name on the side and some plastic styling.
     
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  15. cpt_paranoia

    cpt_paranoia Well-Known Member

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    Beats me what brand you might possibly be alluding to...
     
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  16. gvl

    gvl Super Member

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    In an ideal world all ideal DAC sound the same. In our world ideal DACs do not exist, and ones that do exist have different distortion profiles, so there is some variation in sound.
     

     

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  17. Yamaki

    Yamaki Not For Hire Subscriber

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    I don't know why they sound different to me but I've tried 4 different DACs in my system and I finally found one I liked...well, actually two because they both had the exact same chipset in them.

    Don't know why, don't care why, it's just another component that lends itself to audition so that you can find what sounds best to you.

    One thing I do know is that almost any DAC sounds better if you reclock the signal between the computer and the DAC.
     
  18. RichPA

    RichPA Don't drive angry Staff Member Super Mod Subscriber

    I got my first CD player in 1985, and my first separate DAC in 1991. I've had 9 or 10 DACs since then, and they've all sounded different. I believe there are lots of reasons for that: different chip sets, different digital filter implementations, different rejection of jitter, different analog output stages, variations in power supplies (with some, I've been able to try different power supplies with the same DAC), differences in radiated RF (I had one that would interfere if it sat on top of an FM tuner), and so on. So yes, in an ideal world, they'd all sound the same, but in the world we inhabit, they don't. I expect that the differences I've heard would be imperceptible to some, or that some wouldn't care - I once demonstrated the difference between 2 DACs to my brother, who said "yeah, I hear the difference, but who cares?" I'm happy for now, but I have no doubt that sometime in the future, I'll continue chasing the grail.
     
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  19. Cosmo-D

    Cosmo-D AK Subscriber Subscriber

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    I'll look into it. The RCA model sells for a paltry $199. I haven't built myself a media server yet, so a USB DAC isn't useful to me right at this moment. It's on my list of things to do eventually, but I have so few opportunities to listen to stereo I haven't gotten around to it. When I do listen to something I listen to the entire album, which makes computer-based solution not much more useful than typical CD player.
     
  20. Retrovert

    Retrovert AK Subscriber Subscriber

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    Any commercial product sold via normal retail channels is going to be inferior to the Objective DAC, guaranteed. That's the nature of retail markup.
     

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