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I'm using filter 2. Which I guess is the Denon way as you said.
Thank you for saving me time reading up on the manual. So, as expected, your so call "on/off" is actually filter 1/filter 2 selection.
Now more on your question about the differences, one of the best article I could find on the internet are the following, and it actually uses the AK4490 DAC IC that is used in the original AV8805 and the Denon flagship AVRs so that is good. The ES9018K2M they use now in the AV 10 and A1H is not the same but similar in principle, when it comes to the filter choices.
DAC digital filters part 2 – deeper dive into AK4490 and AK4493 filters - nihtila.com
There are five filters in AK4490, named in datasheet
Sharp filters offer technically great performance and the best measurement results.
- Short Delay Sharp (SD Sharp)
- Short Delay Slow (SD Slow)
- Super Slow
These filters are steep in frequency domain and effectively filter out high frequency components above Nyquist frequency. One reason to start using oversampling DACs and digital filters was to achieve this behaviour and ease requirements for the analog output filter.
While having clean spectrum, tradeoff is excessive ringing in time domain.
This ringing can happen not only after a sharp edge but also before which sounds counter-intuitive – we see the effect of an edge already before the edge. It’s not black magic though but due to long filter length which also delays the signal. We may not see the edge yet but it is already in the filter when we see the pre-ringing.
Slow filters are not as steep in frequency domain so more higher frequency components come through. This can lead to heavily distorted signal on the higher end of audio spectrum.
Flipside here is that time domain looks cleaner with sharp edges without excessive ringing.
In AK4490 and AK4493 there are two different slow filters and one super slow filter.
So, you can see that the Marantz AV8805 has 3 slow filters but there is no option to choose. If I remember right, Marantz used the short delay slow one but I am not 100% sure. No one knows which one of the ES9018K2M filter they used, yet...
Without getting too technical, based on the above, you can see the trade-off and that's really what Marantz's design team was counting on, to give what they claim to have aimed for the Marantz "warm" and "musical" sound vs Denon's. It's not the HDAM nonsense (I am saying this as an EE, but actually based on simple logic that just about anyone can understand if they can read their published block diagrams). It is indeed the slow filter that is responsible. Somewhere in those Masimo video and/or technical articles actually mentioned that, so it's not just my opinion.
Having said that, in my opinion (yes now it is just my opinion, albeit an educated opinion), it's still mainly theoretical. The slow filter, in the AV8805's DAC resulted in a slight roll off, topped out by about -2.5 dB by the time it reached 20 kHz (our hearing limit). The graph below is for the 7705 because Amir did not do it for the 8805, but the results will be identical as frequency response of those DACs are the same, basically flat except when the slow filters are used.
So can we hear the difference between a flat line FR and one that rolls off so slightly, I doubt it, especially if you are over 40.
As for the "ringing" and distortion difference, if you search hard enough you will come across some blind tests done by audiophiles, and there was no evidence that those who claimed to have the golden ears actually pass blind listening tests (unless I missed some.)
In addition, the roll off part really only affect contents with sampling rate 44.1 kHz, at higher rate, even 48 kHz (with Audyssey in use, as an example), FR should be nearly flat even at 20 kHz, and at 88.1, 96 kHz, it will be flat for sure in the audible range so there will be no roll off.
Just an aside, all these, should have no effects obviously, if analog inputs and direct mode are used. So overall I dare say (opinion, not facts) the vast majority of those who heard the "Marantz sound" only heard it because they were conditioned by the hearsay, groupthink on the internet forums and/or marketing info/hype.