Square Wave Hard On

Discussion in 'Measurement Techniques Discussion' started by FidelCastroPS, Sep 19, 2017.

  1. FidelCastroPS

    FidelCastroPS New

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    atomicbob, I saw your measurements of the square wave for Ares, Yggdrasil and Soekris 1541.

    For Ares:

    [​IMG]

    For Iggdrasil:

    [​IMG]

    Soekris 1541:

    [​IMG]


    It appears that only Ares had a near perfect "square" wave. Both Yggdrasil and Holo had a "bass cut" shape (see below). What do you think?

    According to this site: http://sound.whsites.net/articles/squarewave.htm,
    [​IMG]
    Figure 13 - Composite Drawing Showing Common Effects
     
  2. FidelCastroPS

    FidelCastroPS New

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    It appears that only Ares had a near perfect "square" wave. Both Yggdrasil and Holo had a "bass cut" shape (see below). What do you think?

    Correction: It appears that only Ares had a near perfect "square" wave. Both Yggdrasil and Soekris 1541 had a "bass cut" shape (see below). What do you think?
     
  3. Elnrik

    Elnrik Super Friendly

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    We should probably clean this thread up and get some posts moved into a impressions thread?
     
  4. FidelCastroPS

    FidelCastroPS New

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    Here is atomicbob measurement for Modi MB. Aren't Yggdrasil supposed to better than Modi MB?

    [​IMG]
     
  5. atomicbob

    atomicbob dScope Yoda

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    The slope on the square wave response indicates as follows:

    1. modi MB and Ares, they either have a DC coupled output or a VERY BIG output capacitor
    2. for the others, the slope gives some idea of output capacitor size or if DC coupled, servo loop cutoff frequency

    In all cases, power supply stiffness also contributes to ability to reproduce square waves.

    Square wave response is one attribute of a measurement suite. It should be incorporated as a part of DAC evaluation, not used as a single measure of quality.
     
  6. soekris

    soekris MOT - Soekris Engineering

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    Can't see why reproducing a perfect 20 Hz square wave matter, it's not what most people are listening to....

    In the dac1541 case, I on purpose added a 2 Hz 6db/octave high pass filter, don't want DC on the output by accident....
     
  7. msommers

    msommers High on Epipens

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    I asked this question about my DirectStream to Ted Smith, a very respected person in the industry, regarding that website and curve signatures. His response:

     
  8. spwath

    spwath Hijinks master cum laudle

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    really? It's what i listen too. I thought everyone did.
     
  9. Elnrik

    Elnrik Super Friendly

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    I particularly enjoy the London Square Wave Philharmonic's performance of Antonín Dvořák, Sub-bass Quartet No. 12, Op. 96.
     
  10. FidelCastroPS

    FidelCastroPS New

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    From the above very informative comments, it seems that square wave can be affected by:

    1. DC coupled (atomicbob)
    2. Large capacitor (atomicbob)
    3. Power supply (atomicbob)
    3. Filter (Soekris)

    I have more questions:

    1. Since the Modi is newer than Iggdrasil, is Schiit trying to correct the square wave by DC coupled or filter or both? And why?
    2. Based on square wave, how can anyone state this DAC bass is better than the other DAC bass if we don't a reference to compare with.
    3. "By using squarewaves to test equipment it's possible to see a wide range of potential problems, but you need to be able to determine what really is a problem and what is normal behaviour (http://sound.whsites.net/articles/squarewave.htm)." Is there a problem?
    4. Large capacitor and power supply vs DC coupled vs. filter. Which one is better?
     
  11. Elnrik

    Elnrik Super Friendly

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    Sounds like questions that should be in a different thread. This is a loaner thread. These questions don't even pertain to the loaner item.
     
  12. Vansen

    Vansen Gear Master (retiring)

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    Thanks! Loaner threads should be for logistics only!

    If I had the super powers to, I'd move all this out of this loaner thread and into a "Square Wave Hard On" thread.
     
  13. atomicbob

    atomicbob dScope Yoda

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    Thank-you to the staff for moving this to a more appropriate place.
    @FidelCastroPS - you have latched onto an oversimplification of interpreting oscillographic displays. That graphic is intended to give a gross overview of EQ effects only. There is no timebase in the example display from that website for a reason. Please do not attempt to suddenly bridge the gap between an introductory graphic and detailed measurements. You will lead yourself astray. Please go back to the beginning of the posts where the square wave responses you cite were originally posted and read again the top of the first post. Many of them contain a pointer to publications that will help make the leap from the introductory information to the detailed measurements.
     
  14. purr1n

    purr1n Desire for betterer is endless.

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    You have it the other way around. It's less that the square wave is affected by X, but more that the square wave is indicative of Y. At least from a taking measurements POV. A large capacitor or servo (used in DC coupled circuits) may be necessary in some instances to ensure there is no DC, because even small amounts of DC into an amp results in boom! Caps and DC servos will act as a high pass filter, say like pass everything above 6Hz, but block everything below including DC, which is 0Hz. The blocking is gradual, according to a slope, and this may cause residual changes to the shape of a low frequency square wave. (I'm making everything super simplified). Other factors such as the input impedance of the gear that the DAC is driving may also play a factor.
    1. Schiit isn't trying to correct shit. The different square wave might indicate that they used a different method or parameters to couple the output.
    2. No. None of these square wave shapes say anything about the bass.
    3. No. None of these square wave shapes are atypical.
    #4: This is not a which is better question. Again, the square wave is simply information that might tell us something about the design.
    • Power supply doesn't come into play here. There are no abberations in any of the square waves to indicate a problem with the power supply, such as poor filtering, or lack of power.
    • The square wave might give us an indication of the type of digital filter used. Minimum phase, linear phase, maybe slope of the filter if we look closely enough and know what to look for. Whether minimum phase or linear phase is better is a totally different question and better answered elsewhere, although I have strong opinions on it.
    • DC coupled (no servo), with servo, or AC / capacitor coupled? Might be hard to tell servo from cap via square waves. AC coupled or DC coupled, which is better can be up for debate. Designs are based on practicality or cost considerations, which might predicate going a certain way.
     
    Last edited: Sep 19, 2017
  15. FidelCastroPS

    FidelCastroPS New

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    From the web site of a mfg of audio analyzers, Audio Precision:

    Square Waves


    Created on 2009-09-26 14:56:00

    Square waves are useful because they can reveal many things about the frequency and phase response of a system with just visual analysis. This can be valuable when doing a quick system check, or when doing an A/B comparison while changing settings or components. The following graphs highlight just some of the things that a square wave can show:

    [​IMG]

    https://www.ap.com/technical-library/square-waves/
     
  16. purr1n

    purr1n Desire for betterer is endless.

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    Yeah. We know.. You already posted the same thing, from another source, in your first post.
     
  17. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Well, now I am absolutely convinced that the Ares and Modi have to be better than the Yggdrasil.
     
  18. purr1n

    purr1n Desire for betterer is endless.

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    Well, i can't figure out whether Fidel is either eager to learn or just a hard headed numskull, so I am giving him the benefit of the doubt.

    Two things for you Fidel:

    The low frequency roll off is a result of a high pass filter from a servo circuit or cap. This is needed in some circuits to ensure no DC because DC = boom.

    The ringing and the nature of it gives us an indication of the type of digital filter used.
     
    Last edited: Sep 20, 2017
  19. atomicbob

    atomicbob dScope Yoda

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    @FidelCastroPS , I didn't recognize Elliot Sound Products website without taking the time to look at the link. I am going to repeat, verbatim, his introduction to this topic.

    PLEASE READ CAREFULLY, especially the highlighted sections:


    From Elliot Sound Products topic on squarewaves:

    Introduction

    Squarewave testing is a way to test many things at once, but you have to know what to look for. This article explains the many different waveforms you can get from an amplifier or filter, and shows what each waveform actually means. A squarewave is a signal that's rich in harmonics, and because it's symmetrical the harmonics are all odd - 1st (the fundamental), 3rd, 5th, etc. A 'perfect' squarewave has harmonics that extend to infinity, but somewhat predictably perfection isn't attainable. However, most common squarewave generators can easily produce harmonics that exceed the response capability of any audio amplifier.

    By using squarewaves to test equipment it's possible to see a wide range of potential problems, but you need to be able to determine what really is a problem and what is normal behaviour. By necessity, this article has a great many diagrams. most of these will not show the original squarewave, because it's ... well, a squarewave. By themselves, they are decidedly uninteresting, but after processing through a filter or an amplifier we can see the essential characteristics of the device under test (DUT).

    If you've not done any squarewave testing, I encourage you to hook up a few circuits (they are shown in the appendix) so you can experiment. This is an excellent way to learn just how a squarewave can be modified by filters, including tone control circuits which are very enlightening.

    The examples shown here are quite deliberately fairly subtle. In many cases you will see squarewave response that's far greater than shown in any of the diagrams. That doesn't indicate a fault, it simply means that the circuit has more of whatever is modifying the waveform or phase than these examples show. For example, it's easy to get far more treble cut or boost than you'll see in any of the following examples, so you have to learn how to interpret the results.

    You have received a fair amount of information from some knowledgeable people here, but if you want a personal tutorial, you need to do some of the homework yourself before beginning your journey of enlightenment enlisting the help of others here, who are basically donating their time to you.
     
  20. Cspirou

    Cspirou They call me Sparky

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    The Yggdrasil has a discrete output buffer which I believe uses minimal or no feedback. The Modi has an opamp output which is usually designed to be used with high amounts of feedback.

    This could explain why the Modi square wave looks technically better, however doesn’t tell you everything about the sound. Feedback helps with THD but can affect other issues. Each additional component in the signal path changes the sound and there are way more parts that makeup the opamp vs the discrete buffer they use.
     
    Last edited: Sep 20, 2017

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