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MQA is Vaporware


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1 minute ago, John Dyson said:

Keeping significant Gibbs from happening in a substantial freq response cut,  without nonlinear filtering is a 'real treat'.

 

The point is, it takes expertise and good design, but can be done.  Or you can throw out the "good design" and "substantial frequency response cut," and voila! - MQA!

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

Computer, Audirvana -> optical Ethernet to Fitlet3 -> Fibbr Alpha Optical USB -> iFi NEO iDSD DAC -> Apollon Audio 1ET400A Mini (Purifi based) -> Vandersteen 3A Signature.

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4 minutes ago, John Dyson said:

I agree 100% -- anything but a constant delay filter -- commonly called linear phase -- will tend to scramble the arrival of the audio signal on the other side of the filter.  'Sounds good' is sometimes important.  Also, 'Deadly accurate' is also sometimes important.

I really enjoy it when i can simply do a good design when using linear phase filters, but using minimum phase can sometimes be... interesting. 

 

OTOH, if you're making room response filters and trying to correct for timing idiosyncracies....

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

Computer, Audirvana -> optical Ethernet to Fitlet3 -> Fibbr Alpha Optical USB -> iFi NEO iDSD DAC -> Apollon Audio 1ET400A Mini (Purifi based) -> Vandersteen 3A Signature.

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1 minute ago, Jud said:

 

The point is, it takes expertise and good design, but can be done.  Or you can throw out the "good design" and "substantial frequency response cut," and voila! - MQA!

Some really 'uncommon' or 'tricky' design techniques are like a 'secret handshake'.   Figuring out the specific problem about filtering the gain control signals without disrupting the dynamics at all was a major challenge (I didn' t have anyone else to learn from.)  A simple linear phase brickwall won't work - the key is a carefully crafted filter characteristic  -- once the technique is understood, then it becomes one of those Eureka moments.  Now, there is no overshoot in any of my gain control cruves, but also have a nicely limited spectrum -- with absolutely ZERO nonlinear filtering.  *That* was a major breakthrough that allowed me to open up the signal processing opportunities in my project.

 

If I was stuck with IIR filters, even using optimization techniques -- my code would still be in the dark ages.  Imagine doing the advanced  processing in HW?  I cannot even ponder it...  Learn how to use the tools!!!

 

This was slightly off topic -- I am (in my long-winded way) trying to state (and effectively agree with others) that being religious about one technique or another does limit opportunities and choices.  Knowing how to use ones tools -- including something as simple as audio bandwidth filtering -- makes stuff more deterministic, more consistent results, and less snake-oil.

 

None of us EVER quits learning, or if we do -- we then 'fall behind' into obscurity or maybe, start becoming a 'high priest' who knows less and less over time, but still happy to accept money from sponsorships...

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9 minutes ago, Jud said:

 

OTOH, if you're making room response filters and trying to correct for timing idiosyncracies....

Oh yea -- I agree that is a case where both the phase and the amplitude need to be crafted.  It is all about 'knowing ones tools', and being willing to learn how to use new tools (or even, when really necessary -- truly innovate!!!)

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10 hours ago, Jud said:

- In order to minimize aliasing and imaging from ultrasonics, a slow-rolloff filter must start cutting in the audible range. Do you regard a recording rolled off in the upper audible range to be a “typical high-quality music recording”?

 

When it comes to recording with slow-rolloff antialiasing filters, as the original sample rate is generally 2Fs or 4Fs, there is no significant top-octave rolloff in the audioband. For example, the "Listen" filter of Ayre's QA-9 A/D converter with a sample rate of 192kHz reaches –3dB at 70kHz but is flat in the top octave (–0.1dB at 20kHz).
 

With playback of CD-resolution recordings, a slow-rolloff reconstruction filter typically gives a rolloff reaching between 1dB and 3dB at 20kHz. See fig.8 at https://www.stereophile.com/content/mytek-hifi-brooklyn-da-processorheadphone-amplifier-measurements

for example, reproduced below. I doubt that is audibly significant. YMMV.

 

BTW, IIRC it was mentioned elsewhere in this thread that Ayre's Charley Hansen was not a fan of minimum-phase reconstruction filters. This is not correct, as can be seen from the impulse responses of his "Music" and "Listen" filters,  both minimum-phase, at https://www.stereophile.com/content/ayre-acoustics-qx-5-twenty-da-processor-measurements

 

John Atkinson

Technical Editor, Stereophile

1016MyBrookfig08.jpg

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45 minutes ago, Doug Schneider said:
1 hour ago, John_Atkinson said:

With playback of CD-resolution recordings, a slow-rolloff reconstruction filter typically gives a rolloff reaching between 1dB and 3dB at 20kHz. See fig.8 at https://www.stereophile.com/content/mytek-hifi-brooklyn-da-processorheadphone-amplifier-measurements for example, reproduced below. I doubt that is audibly significant. YMMV.

 

If you've ever played with tweeter rolloffs, 1-3dB is significant and clearly audible as you're usually talking about a fairly wide bandwidth in the top octave of the audioband.

 

Fairly wide bandwidth? Not really, Yes, if you are talking about the level of a tweeter, I have found, in a blind test, that I can detect a level difference of just 0.5dB. But that 0.5dB difference covered 2.5kHz-20kHz, ie, 3 octaves, which is a large "area under the curve." In the case of the example of the slow-rolloff reconstruction filter I gave,  the output is flat to 10kHz, -0.1dB at 13kHz, -0.86dB at 17kHz, and -2.4dB at 20kHz, ie, the area under the curve is very small. And that area is in a region where human hearing sensitivity is reduced compared with frequencies below 13kHz. I doubt that it will be audible.

 

John Atkinson

Technical Editor, Stereophile

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