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Slow VS Fast roll off and Minimum VS Linear phase

Discussion in 'Sound Science' started by windowsx, Feb 16, 2017.
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  1. Psalmanazar
    Yes exactly, the minimum phase filters are usually done over DSP but some like the Schiit Fulla and Jotunheim DAC portions use analog filtering. These are cause the destruction of stereo width and imaging with minimum phase filters. Of course it is applied to both channels, I don't know why that was brought up at all earlier in the thread.

    Anyways on a DAC with switchable filters, is easy to hear what the minimum phase filter does (collapse stereo width/imaging on recordings), why it does it (not time-domain coherent), and how it does it (some frequencies are delayed more than others going through the filter). If you have a decently resolving, high-fidelity system and not closed headphones, bookshelf speakers on a bookshelf, or one of those bluetooth amazon/apple pod egg things, it is pretty easy to hear with a DAC that has switchable filters.

    As for the psychoacoustics behind it I don't know. Family Feud style internet sampling done by Archimago? I don't care.
    Last edited: Jun 25, 2017
    Arpiben likes this.
  2. pinnahertz
    I'm not ready to say that humans couldn't hear a difference between a linear phase and minimum phase filter at all, given just the right circumstances. Pretty sure you could show some degree of audibility. But I'm not sure it matters, though, since you're only changing one known filter in a long chain of filters of various phase responses. What you actually hear is a composite filter made up of many cascaded filters, with a composite response. There's no switching a DAC filter to change that, there's already way to much done in the entire chain that you don't know enough about to respond to.

    It's also a well known fact that if you put a switch on a bit of audiophile kit and label it with anything that indicates a change in perception, it will produce an audible change (even if the switch is never actually wired to anything). I actually did this decades ago with a knob in a studio ambiguously labeled "correlation", with 0-10 scaling, and the instructions that it should be optimized for each individual bit of audio being transferred. And it was adjusted, very carefully, and made an audible difference. I never soldered a wire to the pot.
    IBJamon, ThomasHK, abm0 and 1 other person like this.
  3. yage
    The analog filtering is probably in place for reconstruction - that is, to filter out the images centered around multiples of the oversampling frequency and to account for the sample and hold output of the converter. The digital oversampling (low pass) filter is contained in the DAC chip itself, in this case the AKM 4490, and is where you can select from different impulse / frequency responses.

    Personally, I don't think that a minimum phase filter collapses the soundstage, nor does it affect image stability / localization. For example, I thought the Meridian Explorer2 (minimum phase filter) sounded more expansive than the AudioQuest DragonFly v1.2 (linear phase filter). I also haven't noticed the soundstage for music played back on my Oppo BDP-103 to have greater depth or width than my Ayre C-5xeMP. Nor do I have a hard time locating performers within a space on either.

    Archimago mentioned that the Pono's filter as designed by Ayre "does not show significant group delay in the higher frequencies" and consequently "phase shift through the audible spectrum is not an issue."

    Charles Hansen also stated the following in an AudioStream interview:

    "On the other hand, a minimum-phase filter has the same total amount of ringing, but it is all moved until after the impulse. This type of filter does have some phase shift, but it is very small and only at very high frequencies"

    Finally, does this even really matter? There's phase shift in headphones too - look at the impedance / phase plot for the HD 650. Guess which transducers have a fairly flat phase response (at least until the upper frequencies)? Planars. Ethan Winer has noted that phase shift seems to have an effect if it's constantly changing and only if you combine a phase shifted signal with the original signal.
  4. castleofargh Contributor
    as I said in a previous post, my own tests(actual tests recording stuff and abx) resulted in me being able to notice different filters only within my hearing range.
    but there is another important aspect at play here. usually going with some filter decisions will go a different roll off speed. in short a different EQ in the upper trebles. and in some cases the roll off can start as soon 12khz. it's super small of course, but it means we end with both EQ and different phase filter within the audible range. and both have the ability to alter the perceived "image", so the only question is with each implementation, does it reach enough amplitude before it's out of the audible frequency of the listener? from my perspective a proper band limiting should of course be outside, but it doesn't mean all designs are. even more so when you decide to implement filter switch on your system. then of course the more audible it is the better.
  5. Main Source
    Right on man , I dont have my PHD in DAC'S yet and was wondering the same thing, I wish he would just chill out and if he doesnt have an answer, dont reply at all. Instead we get 25 paragraphs of his rhetoric
  6. ev13wt
    Well, this one time in space camp, outside the ISS, ...

  7. bigshot
    Square waves come out of my speakers when I play Lawrence Welk records!
    buonassi likes this.
  8. skwoodwiva
    8QUOTE="Psalmanazar, post: 13564329, member: 433497"]That is the dow
    nside of minimum phase filters; the change in arrival time of different frequencies is not uniform and greatly affects the perceived stereo image. Yes DACs with minimum phase filters will apply it to both channels and yes it collapses the stage almost always when compared to the linear phase one in the same DAC. There does not need to be a difference between channels, the stereo image is already messed with. Try ABing it yourself on something with switchable filters and you can hear instruments in a multitrack recording no longer be as well delineated and will usually move closer to the center. NOS DACs tend to be much much worse things than ones with minimum phase filters though.

    There are some youtube videos that show the benefits of minimum phase filters applied to single instrumental tracks in mixing but they are not good for stereo recording or listening overall. The one benefit for consumers is that they can tame overly forward/bright DACs like ESS Sabre 9018 or poorly implemented Wolfsons. They are also good for brighter headphones like the stock HD 800 or Beyerdynamics. Yes it's not very high-fidelity to mangle the phase but it can result in more pleasing sound. Best thing to do though is simply not use super bright gear like that you have to work around the flaws like that though.[/QUOTE]
    Old but good thread. Thank you for the elucidation on filters.
    I assume proper source music, say a 2 miked recording is a given to even notice a differance.
    How can "some member's" muli miked sources even convey a stereo image that is not marred to start with?

    Thanks to @WindowsX for asking.

    Much flak & bigotry is here too. ..
    I guy ask a good Q! But let it be a stupiid one, (the one being stupid is the reciever btw) ,

    He finally gets a good answer. & look at the trolls along the way. ....efing trolls
    Last edited: May 6, 2018
    WindowsX likes this.
  9. Joe Bloggs Contributor
    Apparently it is a good answer if it fits your preconceptions and a bad answer otherwise (even if it comes from a manufacturer representative of not one but two DAP manufacturers)

    Last edited: May 6, 2018
    skwoodwiva likes this.
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