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  1. #1
    Senior Member ralphpnj's Avatar
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    Quick question about DAC "filters"

    i just finished reading a really poorly written review of Auralic's Altair streaming DAC and in the review extensive coverage is given over to the various filters in the unit.

    So my question is:

    How are these "filters" different from a simple graphic equalizer or simple DSP or even, god forbid, tone controls?

    Note: the review is the March 2017 issue of Stereophile.
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  2. #2
    Senior Member pablolie's Avatar
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    I haven't read it. I subscribe to Stereophile, but don't read everything in it... shall try tonight

    But in a perfect world, I'd like this simple feature in a DAC+Preamp, or in an integrated DAC+Amp unit built into active speakers:

    * High quality and configurable (30-40-50-60-etc) frequency divider in the digital domain with both analog and digital *dual* outputs, one for low and one for high domain. Some audiophiles may prefer more, but beyond 3 I never would see the point.

    * Option for room optimization in both domains.

    My current main setup [see sig] provides me with the output options, but not with the built-in configurability. I drive my speakers full range, and optimize the sub on the side of it. The system I set up at my SO's place (NAD D7050 integrated amp) allows for total optimization [1]. You can configure the cutover freq. That said, my system sounds better. But I would love for a next gen Benchmark to provide those options for experimentation. They are shipping the DAC3 now, but I will very much pass. Good DACs sound pretty much the same. The only thing that IMHO could make them sound better is built-in DSP for (a) driving subwoos, and (b) room correction.

    [1] After a lot of playing around at my SO's place (she doesn't even bother or notice, she's perfect) I have established the divider in the D7050 is so-so, it seems with good speakers the best option is to go full range on the speaker, and do the usual seat-of-the-pants groundwork for the supplemental bass with subwoo.
    Last edited by pablolie; 2017-02-15 at 21:57.
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  3. #3
    Senior Member Mnyb's Avatar
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    Quote Originally Posted by ralphpnj View Post
    i just finished reading a really poorly written review of Auralic's Altair streaming DAC and in the review extensive coverage is given over to the various filters in the unit.

    So my question is:

    How are these "filters" different from a simple graphic equalizer or simple DSP or even, god forbid, tone controls?

    Note: the review is the March 2017 issue of Stereophile.
    They are probably talking about the DAC 's reconstruction filters both the digital and analog part, the measurements side note did it have a lot of different impulse responses ? They are a necessary part of every DAC ( except some NOS DAC's but they are broken by design )

    These are not really eq filters but the final stage in giving you a nice analog signal after the DAC process without ultrasonic gunk in the signal .
    The hot topic a couple of year have been these filters impulse response and steepness and resulting ringing fancy terms like "apodizing" is used . In some cases like Ayre DAC they even sacrifice the hf response a bit to get less ringing .

    And also how they are implemented in the chips or software is point in good DAC design .
    Not just the chosen filter topology but how you do it , for example the dreaded intersample overshoots you can get if these filters have no margins for very high levels in the signal and you are oversampling .
    It can be done better with floating point math in software instead of hard wired digital filters ? Or can it ?

    Some extrem setting can be "EQ like" in the highest treble , there is always some trade offs between frequency response phase response and ringing .

    The ringing in DAC filters has always been assumed benign as the frequency of it is above human hearing and you have pre and post ringing in these impulse response test .
    Which are just test this kind of signal is not present in music the DAC normally converts ( due to normal ADC filtering when recording) but a way to test one property of the filter .

    Meridian and Ayre and some others argue that apodizing aka no pre ringing sounds better even if it sacrifices performance elsewhere

    All in all usually very subtle differences if they are at all audible .
    In the old days a thing the DAC designer just decided for the design at hand .
    Now for good and bad it's a knob to twiddle on some DAC .

    And in software if you oversample with Squeezelite on PI based player you got the whole range of possibilities to twiddle with for yourself a real handful the SoX lib can any filter you like ? I'm testing it to remove my MeridianG98DH ovesampling of inputs by letting Squeezelite do it with the important diff of -3 dB attenuation to handle intersample oversshots
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  4. #4
    Senior Member Archimago's Avatar
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    Quote Originally Posted by ralphpnj View Post
    i just finished reading a really poorly written review of Auralic's Altair streaming DAC and in the review extensive coverage is given over to the various filters in the unit.

    So my question is:

    How are these "filters" different from a simple graphic equalizer or simple DSP or even, god forbid, tone controls?

    Note: the review is the March 2017 issue of Stereophile.
    Hey Ralph,
    Like Mnyb said, they're just referring to variations of the digital oversampling antialiasing filter used in the DAC. Subtleties like the presence of pre-ringing in the impulse response, passband, length of filter can change the frequency response and determine how well aliasing distortion is filtered out when the signal is upsampled.

    My post this past week on the blog models what is seen with the MQA filter for example:
    http://archimago.blogspot.com/2017/0...ilter-and.html

    SoX can do it but if you want a bit more control with the GUI interface, iZotope RX does a great job with modelling the filter parameters. Have fun experimenting and seeing if you can hear the difference.

    Bottom line - unless you really fool around with the parameters and strongly affect the frequency response (like with Ayre's filter and the PonoPlayer), you're not going to hear much difference. If you play a very loud track with clipping and square waveforms, then you might see the ringing in the upsampled signal as well as intersample overload distortions. With properly low-passed signal (as in all frequencies <22.05kHz in a 16/44.1 file), then there's not going to be any ringing in the output...
    Archimago's Musings: (archimago.blogspot.com) A 'more objective' audiophile blog.

  5. #5
    Senior Member Wombat's Avatar
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    When people know what filter they play they will tell you all kind of stories.
    When people don't know what filter they play they dig in the dark.
    Like Archimago pointed out there can be filters that change parameters very much so things like frequency response or phase can be audible.
    Only the legendary Maridian filter listening test had a tiny positive pecentage positive result with very steep, strong ringing from upsampling.
    Forget about the nonsense people wirte about every tiny parameter in a filter changes the sound.
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  6. #6
    Senior Member Archimago's Avatar
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    Quote Originally Posted by Wombat View Post
    When people know what filter they play they will tell you all kind of stories.
    When people don't know what filter they play they dig in the dark.
    Like Archimago pointed out there can be filters that change parameters very much so things like frequency response or phase can be audible.
    Only the legendary Maridian filter listening test had a tiny positive pecentage positive result with very steep, strong ringing from upsampling.
    Forget about the nonsense people wirte about every tiny parameter in a filter changes the sound.
    Yeah, that epic Meridian listening test that also either truncated or used rectangular dithering that they admitted were suboptimal.
    Archimago's Musings: (archimago.blogspot.com) A 'more objective' audiophile blog.

  7. #7
    Senior Member Wombat's Avatar
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    Remember the "Ringing Less" filter you tested? http://archimago.blogspot.de/2016/10...o-pcm5122.html
    Alone the positive name of the filter had effect on the listener that reported its 'better' sound it seems.
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  8. #8
    Senior Member Wombat's Avatar
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    Quote Originally Posted by Archimago View Post
    Yeah, that epic Meridian listening test that also either truncated or used rectangular dithering that they admitted were suboptimal.
    Or simply the used beryllium metal tweeter distorts different with or without HF content.
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  9. #9
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    Quote Originally Posted by Archimago View Post
    Yeah, that epic Meridian listening test that also either truncated or used rectangular dithering that they admitted were suboptimal.

    Also significant was the fact that they used ultra-sharp, narrow bandwidth filters that generated a lot more ringing than just about any real world DAC.

  10. #10
    Senior Member Archimago's Avatar
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    Yup... Good points all.

    Bottom line: The Industry needs us to believe the filters are a "big deal". After all, how else to differentiate digital audio of which essentially any decent DAC over the last 20 years has sounded very good already!? Maintaining this sense of wonder and belief in claims underpins many of the advertised benefits for companies as disparate as PS Audio, Ayre / Pono, Meridian, T+A, Chord all the way to MQA and its promise of "revolutionary" sound quality.

    What the audiophile world truly needs to evolve and "revolve" is a realization of the objective mindset in terms of adjudicating the engineering around devices and file "formats". Time for the pendulum to swing back to objectivity... A long time coming but I remain hopeful that we can all contribute to making an impact.
    Last edited by Archimago; 2017-02-18 at 15:06.
    Archimago's Musings: (archimago.blogspot.com) A 'more objective' audiophile blog.

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