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Thoughts on a bunch of DACs (and why delta-sigma kinda sucks, just to get you to think about stuff)

Discussion in 'Dedicated Source Components' started by purrin, Dec 5, 2013.
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  1. prot
    This thread is getting so serious .. Next time you know someone mentions DBTs and we all end up in the dark science section.

    Heeey! That was my beer!

    Were was I? Ah ya, life is dangerous...

    Wait, you did not get that? ... wait ...
     
  2. jcx
    perhaps not too far afield - feedback theory is central to the internals of Delta Sigma converters and of course the analog buffers, I/V converters and filters after (almost) any DAC will employ feedback in some form or another
     
    virtually all useful active circuits use negative feedback - the audiophile marketing "no feedback" really at best means no Global loop feedback and ignores local degeneration that feedback relations are needed to describe fully
     
    but it is too big a subject to do justice to in any depth here
     
    I did find the Pass audio distortion and feedback article unfortunate - I did press him over on diyAudio and he did admit my points of criticism - I consider his "exaggerating for effect" as pandering to the expected biases of the audiophile magazine audience
     
    the "trick" for correct analysis that Pass skated past is that the signal level decreases by the gain of the intermediate stages as you follow the signal backwards from output to the input of a high loop gain global feedback amp
    the reduced signal levels hugely reduces the distortion generation in each stage - at the input even undegenerated bjt diff pairs can add less than -120 dB distortion to the difference signal under ordinary operating conditions
     
    there is no "tsunami" of IMD products in well designed high feedback amps operating within their limits - until you clip or try to "correct" a deadband
     
    I do link, recommend just about everything else Pass has published
     
     
    Putzeys feedback paper is a much more reliable popularization for audio enthusiasts with some EE knowledge - still not enough to learn the subject from http://linearaudionet.solide-ict.nl/sites/linearaudio.net/files/volume1bp.pdf (only a little bit of Laplace transfer function math...)
     
  3. evillamer
    Here's another article on Sigma Delta Conveters:
    https://www.eecs.qmul.ac.uk/~josh/documents/Reiss-JAES-UnderstandingSigmaDeltaModulation-SolvedandUnsolvedIssues.pdf
     
    In the article, it mentions several issues with sigma delta:
     
     
  4. Ableza
    ... or someone will soon state the old audiophoole lie, "We really don't know how to measure everything in audio."  It always happens.
     
  5. Sapientiam
    OK I'll bite - 'we currently have no measurement for how well an amplifier conveys a recording's soundstage'.
     
    Articnoise likes this.
  6. Ableza
    HA HA HA!  Define the electrical signal properties of "soundstage."  Or even the acoustic field properties of this thing.  :)
     
  7. Sapientiam
    If I knew what the electrical signal properties of a recording's soundstage were I'd come up with a measurement.
     
  8. evillamer
    I think soundstage can be defined by the accuracy/resolution of the dac in reproducing the tiny plankton details accurately at the decay & release of the sound envelope. From my (rudimentary) understanding is Sigma Delta averages/smoothes things out using a feedback & noise shaping or some sort clever engineering tricks(which I understand that R2R DAC doesn't do this). Not sure if that averaging/noiseshaping/filtering affects the ability to reproduce very tiny(micro-rapid) changes in the soundwave accurately. 
     
    of course there are many other dac performance aspects like(e.g.) stereo channel separation and IMD that also affects soundstaging.
     
     

     
     
     
     

    Measuring reverberation time




     

     
     
  9. DreamKing
    The problem is that you're using a perception-based term that has nothing to do with science. You will never be able to effectively measure it. It needs to remain the same, under the same conditions no matter what.
     
     
  10. Sapientiam
     
    I agree its perception based but disagree that perception based things have 'nothing to do with science'. Some cognitive scientists are studying how perception works, in detail. To me it does sound rather defeatist to say I'll never be able to measure it effectively.
     
  11. DreamKing
     
    I'm saying soundstage isn't a scientific term (applied science). Too vague and varying to be measured. It's like saying you're gonna measure prat one day, even more confusing.
     
  12. jcx
    the Smyth SVS Realizer is a practical demonstration that typical electronics don't seem to have a big problem with presenting a convincing synthesized soundstage of a specific set of loudspeakers in a real room
     
    they sidestep a lot of the modeling with real measurements, mics in your ears in the real room, in front of real speakers from mono up to 7.1 multichannel setups and calibrate as you turn your head through specified range of angles for your personalized hrtf
     
    then they do the same for your circumaural headphones - they supply a Stax Lambda system as a default for those without their own preferred audiophile cans and amp
     
    the result is very good - you can localize the virtual speakers as well as the real, compare in seconds by just lifting the cans off your head, tilting them down so the head tracker can't see the target
     
    the reductionist position is that good electronics, a complete ADC/DSP/DAC chain inserted gives "out of the head" stable, "realistic" soundstage of "those speakers over there, in this room" - because the phase, frequency response conditions needed for the amps ADC and DAC are trivial
     
    http://smyth-research.com/technology.html
     
    after hearing a full personal calibration demo of the full Smyth system in a 5.1 setup it is ROTFLAMO funny reading most Head-fi "soundstage" discussions of even headphones, much less claims that specific amps have a serious role in "correcting" soundstage, "in synergy" with certain cans
     
    at least crossfeed circuits or plugins, Dolby Headphone make real differences - but still are pale shadows of what the Smyth Realizer does with personal calibrations and active headtracking
     
    maverickronin likes this.
  13. DreamKing
     
    I think the booming VR development is going to introduce competition to the Smyth Realizer as well as more binaural content. It's the best thing that can happen. It won't be about replicating speakers for headphones soon but binaural content (much more of it and hopefully not just for video games) and hardware based on individual binaural HRTF. 
     
  14. evillamer
    On the topic of soundstage:
     
    Although this is marketing video(at the very end of the video), It has quite valuable information with regards to how we perceive sound. see it for yourself.
     
     
     
    longer video for those interested in speaker room accoustic:
    https://www.youtube.com/watch?v=BroP_iFVJvo
     
  15. BassDigger
     
    Bite No.2:
     
    What difference does it make, for you? That sand must be really clogging up your ears! [​IMG]
     
    head_in_the_sand-461x307.jpg
     
    Saying that we can measure everything is surely like saying that we understand everything.
    Who is ultimately the better scientist, one who thinks that he does or doesn't understand?
     
    Wildcatsare1 likes this.
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