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Discussion in 'High-end Audio Forum' started by magiccabbage, May 14, 2015.
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  1. Rob Watts
    I have been asked this before that somehow the extra depth of my DAC's - and most particularly with Dave - was due to something added within the design. Now it is very easy to create a false sense of depth by simply adding reverb, and this of course may be done easily with the resources one has on a big FPGA. But I can prove this is not the case - simply by using flat as a pancake recordings. So Jazz at the pawnshop, is in a small venue, and should sound like it has little depth - and that's exactly how it sounds on Dave - it sounds like a small environment. When you use close miked recordings that have no added reverb it sounds completely flat, that is the sound is exactly in line with the speakers. Now if I had used some tricks to artificially enhance the depth, then everything would have more depth all the time. But this categorically does not happen with Dave - flat recordings that have no depth, has no depth, instruments that have depth will be accurately portrayed with depth.
    This brings me on to the most important point about subjective evaluation - to know something is better for sure (that is its not some kind of system optimisation) is variability. Then one can be sure the improvement is a fundamental step forward in transparency, rather than some fine tuning that suits the product at that time with that particular system. So I am trying to maximise the range of depth that can be heard, from completely flat to sounding miles away. And in this sense, Dave is much more varied in depth perception than any other DAC I have ever designed - by a massive margin.
    The technical reasons why depth is compressed in DAC's I understand, and its absolutely nothing to do with ringing or time domain behaviour (this will affect lateral imagery and height though) but is down to how accurately small signals are reproduced. Small signals are normally distorted, and have an amplitude that is modulated or changes with level. It's these tiny changes in amplitude that confuse the brain that stops one perceiving depth properly.
    The interesting thing I learnt with Dave is that there is no limit to how accurate small signals need to be for the brain to properly perceive depth. This is actually quite an amazing and surprising statement; normally you can get to a limit where reducing a distortion or error no longer has an effect; but - and this is the stunning thing - this does not seem to apply about depth perception. There is something truly amazing about how the brain accurately resolves and measures depth.
    Delta-sigma DAC's fundamentally have the capability of resolving small signals much more accurately than R2R or ladder DAC's as ladder DAC's are poor for small signal accuracy due to the impossibility of matching the resistors. Having said that, delta-sigma is not a panacea, to actually resolve depth properly requires a lot of care and effort, as minute errors will have an effect.
    Its way too complex to talk about all of the issues involved in DAC design to properly resolve depth information, I think I will talk about it in a future blog article.
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  2. isquirrel

    Thanks Rob, looking forward to that article. 
  3. isquirrel

    Would you say that the single ended outputs are sonically superior to the balanced outputs?
    To-date I have not felt the need to use an external amp, I am amazed at well the DAVE drives the Abyss. I thought for sure it would struggle it almost produces as much gain as my Woo Audio 234's on full Plate settings. Actually I will post a photo just so people can see how far I have the volume knobs turned around on the Woo's, compared to the same volume at 0dB on the DAVE.
    I find myself wishing for a Chord Headphone amp to use with other DAC's.
  4. wisnon
    Paul, the Nagra Dac is very vey good as well. Had a demo evening with it last year at Stenheims in Switzerland. The only obvious weakness is the lack of DHT tube rolling like in the Lampi. DHTs are magic.
  5. Frank I
    I think both were good. I used the  headphone with the balanced outputs and speakers with headphones single ended,But the amps were different with the balanced output.  Hard to say which was better but I dont think anyone would be unhappy either way.
  6. isquirrel

    Sorry if I have mis-understood you, but are you saying that you ran the Headphones out of the balanced outputs ?
  7. Frank I
    I ran the Cavalli amp with the DAVE as a DAC- for headphones only. I used the single ended with the Tube amps and speakers and headphones.
  8. isquirrel

    Thanks Frank for the clarification.
    Hopefully you will be reviewing Audeze's the" King" in the not to distant future.
  9. Frank I
    it could be interesting to review that piece. Hopefully they have it at the Headphonium in Newport Beach in June
  10. rkt31
    IMHO chord DACs by using longer tap length and elaborate digital filtering can accurately represent the timing which is only possible by this approach . that is why other DACs in similar or expensive price range can't match the depth and transparency provided by chord DACs . I still believe that even mojo can beat 'that' dac purely for sq at 1/5th or so price. yesterday mojo via uapp sounded sublime with some of the piano music. the kind decay I get for piano notes is next to impossible by any other technology on hand except in these chord DACs .
  11. Crgreen
    Is the Dave a balanced circuit? My experience has been that balanced circuits tend to sound better with a balanced connection and singly ended circuits with a single ended connection. On slight practical advantage for me would be that the balanced output is a whopping 6mv. I wonder why Rob said he thought the single ended output was better? Like so much else, there's no general consensus in respect of balanced v. single ended outputs.
  12. shuttlepod
    If this is the case, one must assume that the perception of depth is strongly correlated with the evolutionary survival of the species. In other words, the human ability to pinpoint sound at varying degrees of depth must have evolved into a finely honed ability because it enhanced our ability to detect threats to our survival over the millennia. 
  13. JaZZ Contributor
    Indeed! [​IMG]
  14. Sunya
    Rob, could you say what made you decide on the LX75 FPGA when there is also the double the size (and double the cost) LX150? Was it simply a cost issue (though at Dave's cost it shouldn't have been) or the bigger FPGA just wasn't needed for your filter and noise shaper?  I'm thinking you could have made an even longer filter with 300k+ taps on the LX150; would it have taken too much time to code?
  15. romaz
    The balanced output on the DAVE isn't a whopping 6V rms, it's an even more whopping 12V rms but it comes at the expense of a loss of transparency as there's an extra OP amp in the analog signal path to go balanced.  SE output is 6V rms.
    DAVE is SE by design and here is why Rob designed it this way:
    "Well this is a complex subject, and sometimes a balanced connection does sound better than single ended (SE) - in a pre-power context - but it depends upon the environment, and the pre and power and the interconnect. But the downside of balanced is that you are doubling the number of analogue components in the direct signal path, and this degrades transparency. In my experience every passive component is audible, every metal to metal interface (including solder joints - I once had a lot of fun listening to solder) has an impact - in case of metal/metal interfaces it degrades detail resolution and the perception of depth. So going balanced will have a cost in transparency.
    In DAC design, going balanced is essential with silicon design; there is simply too much substrate noise and other effects not too. But with discrete DAC's you do not need to worry about this, so going SE on a discrete DAC is possible, and is how all my DAC's are done. But differential operation hides certain problems (notably reference circuit) that has serious SQ effects; so going SE means those problems are exposed, which forces one to solve the issue fundamentally. In short, to make SE work you have to solve many more problems, but the result of solving those problems solves SQ issues than differential operation hides when you do measurements.
    In the case of Dave, I have gotten state of the art measured performance - distortion harmonics below -150 dB, zero measurable noise floor modulation - and there is no way you could do this with a differential architecture. So it is possible to have better measured performance with SE than differential, but it is a lot harder to do it - indeed, the only way of getting virtually zero distortion and noise floor modulation is SE.  
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