Filters called ‘apodizing’ were Peter Craven’s invention in around 2003. They have since been incorporated in many digital products to eliminate pre-ring (but not post ring).
Peter Craven is one of the MQA inventors. The filters in MQA have the same effect, eliminating pre- and post-ring but are not the same design.
Well the newer “minimum phase - slow roll off” filter on my DAC
does make any PCM sound the same as MQA.
Not that I like it or want to use it as I hate blur created by non-linear filters. Unfortunately all filters in MQA are non-linear so MQA => 
1 Like
Nonsense.
- Peter Craven did not invent apodizing filters.
- Apodization has nothing to do with eliminating “pre-ringing”. A symmetric windowing function will have pre-ringing. Apodization has to do with eliminating spectral leakage.
2 Likes
That seems to be the “secret sauce”:
- minimum phase = eliminate “pre-ringing” at the cost of messing with the time-domain behaviour.
- slow rolloff = lots of aliasing of ultrasonic garbage into the audio band.
Archimago had a couple of posts about MQA’s reconstruction filters. They are, necessarily, speculative in nature. But I think they bear out your observations of the the MQA “sound”.
3 Likes
The filter terminology ‘apodizing’ was borrowed from radar antenna design and introduced into audio to resolve pre-ring. See above papers.
So many errors.
MQA filters are linear phase splines with a small minimum phase flattening filter; they don’t have the same properties as minimum phase.
Slow roll-off do NOT introduce ultrasonic garbage into the audio band. Ignore some of the nonsense from the individual you cite - he doesn’t understand the difference between audio signals and full scale sine tones. He also doesn’t understand psychoacoustics.
A single minimum phase filter used in the DAC is nothing like the full range of what MQA does. Trying to equate them sonically is pointless.
I stand by what I said.
- An apodizing filter can be causal (no pre-ringing) or acausal. The two have nothing to do with each other.
- And apodizing filters for digital audio were in use long before 2003.
Show history. There was no use of the term in audio that I’m aware of prior to Peter Craven’s use of it.
Slow roll-off means weak anti-aliasing. That’s Digital Signal Processing 101. Throwing the phrase “psychoacoustics” into the discussion is just puffery.
1 Like
I’ve designed them and understand it well. Folding anything back into the audio band that is 40-80 dB below the noise floor is inaudible. That’s why comprehension of psychoacoustics is important. Psychoacoustics is used all the time in audio design, hardware as well as software.
BTW, even in conventional PCM filtering, no matter how steep the attenuation is in the stop band, there is always some degree of aliasing folding back into the audio band, it is just at a low, inaudible level and so irrelevant.
I would if I was a member of AES, $33 per paper is a bit steep.
To which I say, “huh?”
Where do you get that the ultrasonics are 40-80 dB below the noise floor? If they were, there would be no need for an anti-aliasing filter in the first place.
The ultrasonic region from 24-48kHz is not the issue. The regions above that, after filter attenuation, are a different question. It also depends on the ratio of sample rates, measured noise floors, how far humans hear below the noise floor, and so on. Remember that audio sources (not test tones) roll off in amplitude at a 1/f rate,
I can tell you that the team that designed MQA understands all of this well and are not going to fall into DSP 101 problems.
What they “know” and what they are willing to foist off on an unsuspecting public are logically (and ethically) independent.
2 Likes
It’s sad that it appears so easy to besmirch the reputation of people who have been highly regarded, scientifically and ethically, over decades. Too much of it IMHO relates to our online culture of sounding off at everyone and fostering echo chambers with thriving conspiracy theories. People need to calm down.
1 Like
I’d like to see them step up and defend their product, not just release more marketing material full of redefined audio terms.
5 Likes
I see many people who are just expecting the improvements MQA promises: that “better than CD” quality without an MQA decoder.
And when they notice they are not getting this they start hoping an MQA decoder will make up for that and they buy one.
And if after that the quality is still not the “better than CD” (or even “equal to CD quality”) … they start or join threads with titles like “mqa disappointing”.
Not one well educated scientific explanation is changing that.
If quality was better, such threads would not even exist or die soon.
3 Likes
People still argue about vinyl and digital, stereo and mono…
3 Likes
Folks, it looks like this topic has gotten a bit heated over the past day or so. I’ve cleaned up and deleted a few posts to get things back on track.
Please keep it civil with each other. 
2 Likes
Does anyone here know if MQA is generated from digital masters only, or if they, where analogue master tapes exists, use those?