DAC Amp Measurement Methodlogy and Equipment Discussion

Discussion in 'Headphone Amplifier Measurements' started by schiit, Nov 5, 2015.

  1. Cspirou

    Cspirou They call me Sparky

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    Yeah, just noticed that the Sigzig is only 8khz. Its more for chemistry experiments.

    For the bitscope however I can't find much info on the bit depth. I know it can do at least 16 bits.
     
  2. ultrabike

    ultrabike Measurbator - Admin

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  3. purr1n

    purr1n Finding his inner redneck

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    Really two different functions between a scope and analyzer. I'll need to get a scope eventually.
     
  4. Cspirou

    Cspirou They call me Sparky

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  5. ultrabike

    ultrabike Measurbator - Admin

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    LOL! Don't worry at all. Those are very interesting products.

    So far hard to beat the QA400 in it's price point as an audio analyzer.

    I'm starting to appreciate the loss when Creative decided to drop the ball on the E-MU products.
     
  6. firev1

    firev1 Friend

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    Come to think of it, went back on my archives and I actually did document the effect of having two usb devices on the same bus/machine. Similar to what is happening here. Separating the signal generation and acquisition machines did the trick. I'm fortunate to have 3 relatively modern laptops lying around for the task. One way to resolve it is to off course, galvanically isolate one of the devices but that is ultimately a compromise imo. Wyrd has no effect on that sort of issue if I remember correctly need to investigate this again.

    Also as Schiit has said before, no usb audio devices should be on a usb 3.0 bus.

    Also QA401 announcement for those who missed it, improved specs, overload protection+attenuation , differential inputs(probably single end compatible by grounding the negative end) and isolated usb interface as well.
    http://www.quantasylum.com/content/Home/tabid/40/EntryId/36/QA405-and-QA401-Status.aspx
     

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  7. lm4der

    lm4der A very good sport - Friend

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    What? Is this true? And if so, why?
     
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  8. Tuco1965

    Tuco1965 Suffring from early onset Alzheimer's - Friend

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    I know that I've never had luck using USB 3 ports for my Dacs. No problem with 2.0 though.
    http://schiit.com/faq/usb-problems
     
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  9. firev1

    firev1 Friend

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    I'm not clear of the reasoning but some portable dacs really don't like usb 3.0 ports, makes them output more noise. I would only use it if my audio device is usb 3.0 rated.
     
  10. Ormia

    Ormia Rando

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    Wow! Way cheaper than National Instruments stuff. I wish I could use use that audio analyzer for the things I do at work.
     
  11. Thad E Ginathom

    Thad E Ginathom Friend

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    From the Schitt FAQ page, the reasoning is that some USB3.0 computer ports are not actually properly backward compatible with USB2.0. Thus it is not an audio issue in itself, and maybe they cause problems with other USB hardware. That's a huge blunder by the motherboard manufacturers.
     
  12. firev1

    firev1 Friend

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    Wish I could reproduce the measurements now but I could not get any decent JTest done on usb dacs on a usb3.0 port. But thats for only one machine and I'm unsure whether its an issue that affects just my laptops usb card or its a usb3.0 issue. I could still interface with the DACs but its just I get generally shitty results on them.
     
  13. thune

    thune Friend

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    I'm no nwavguy minion, but the postulate was very clear: there exists a set of specifications for which all devices meeting or exceeding those specifications will be indistinguishable in DBT [the so-called transparency criteria.] One of the corollarys is that performance better than required is also unnecessary. It is fully appropriate to call out self-proclaimed followers for claiming that performance exceeding the 'minimum requirements' is an improvement. Another corollay: there is nothing to be said about devices failing to meet the criteria, except that they may be distinguishable in DBT from each other (and from "transparent" devices) and that one may be preferred over the other. [From this perspective, only the Ifi and the grace on USB would not meet the criteria (be distinguishable). The others would simply be proclaimed transparent and indistinguishable.]

    My point: there is nothing to fear from people 'going full-nwavguy' since the perspective is actually narrow and self limited.
     
    Last edited: Nov 7, 2015
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  14. Thad E Ginathom

    Thad E Ginathom Friend

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    by "not an audio issue in itself" I didn't mean "not an audio issue," but, "a general compatibility USB3/USB2 issue affecting audio and, perhaps other hardware too."

    I'm still in the world where the blue socket is an extra on the machine (have one USB3.0 hdd) and I have plenty of USB2 ports to choose between, but... if a person has a new laptop which is all usb3, and that doesn't work properly for audio... that sucks bigger than USB1 did :mad:.

    Is it a hardware problem? Or an OS thing? Does somebody here know?
     
  15. OJneg

    OJneg The Most Insufferable

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    I think you went full-circle and proved the point for us.
     
  16. purr1n

    purr1n Finding his inner redneck

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    I get the opposite effect.

    From external laptop (not plugged into AC) and into PC/QA400
    grace ibm.png

    From PC into same PC/QA400
    grace pc.png

    Laptop to same laptop will look similar to above.

    I figured I might be getting better results with the same PC because they have the same ground and that spuriae from the external laptop might be because the laptop has a different ground potential. USB is screwy.
     
  17. firev1

    firev1 Friend

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    Yeah USB is really screwy and I feel like you are kinda stuck in a catch 22 with no easy way out. More than one usb device = spuraie, separating devices = ground issues. The 0404 had ground lift switches to float the inputs so I can play around with them to avoid those issues. Ugh thats why dac amp measurements are so tough. Looks like for the QA400 the only real way is to use it with a differential front end(designs on diyA) to be able to separate them (generation and DAQ).

    Are the measurements that bad even with your differential probe?

    I have been using the method I described for all my old measurements after all.

    Also I have been toying around with a couple of ideas (in head) for a while.

    1.Using the ADS8881evm-pdk as a 1Msps 'oscilloscope' or probe to look at stuff from DC to 500khz.

    2. Also using another evm pdk but ADS9110 with an AMB labs alpha 24 line stage and 4:1 voltage divider more complex and cost but will be able to 'look' to 1Mhz with the 2Msps rate. Also inherently has much lower noise and somewhat lower distortion than the ADS8881.

    Just throwing out a couple of ideas which are not very practical(sole purpose for instrumentation) but really excites the measurebator in me.
     
  18. logscool

    logscool Friend

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    I'll definitely be looking at getting a QA401 when it comes out looks like a pretty interesting piece of hardware, not quite as good as what the QA405 was supposed to be but honestly with the exception of the lower +-6.5v rail power supply. I've also got a few Tek 2465 (standard and A models), a couple of them need to be repaired but I have one functional standard 2465 which has great performance the only downside is it's got no digital storage capabilities so waveform capture is limited to taking a picture of the CRT and single shot capture is even harder.
     
  19. SKiring

    SKiring Friend

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    It's hardware, it's only an OS problem if the USB is not getting enough power due to the OS (IE: power saving mode etc.) or the drivers are having problems. This is also rarely the case in today's motherboards. Looking at any given H97/Z97 or Z170 board made today the chances of having a non-backwards compatible USB 3.0 port is extremely rare. Same goes for modern day laptops.
     
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  20. BioniclePhile

    BioniclePhile The Terminal Man - Friend

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    I had been wondering about measurements with some Eddie Current amps, and some of the Schiit ones too. There aren't a lot of measurements for amps here so far, especially in comparison to the DACs. I'm pretty sure we've summed up Schiits Multibit superiority a few dozen times over by now. :p
    I'll even send in my Liquid Carbon for measurements in the future if one of the measurebaters didn't order.
     

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