NAD M66 - finally someone makes a decent 2-channel preamp!

[Nocko!]

unless I deactivate the Dirac filter.

Lost track somewhere...but if I remember well, I could hear differences in sound when playing with the app or Dirac, even when I was in "analogue direct mode".
Isn't it that what you are talking about: You are listening to a source in "analogue direct mode" and the sound changes when you engage or disengage a Dirac filter or change the subwoofer settings within in the app?
Nocko!

P.S.: I'll come back to your private message!

 

[Hear Here]

I'd have to disagree on the Dirac Live taking "life out of the music" and the "entire frequency range has to endure the filter".In all the REW measurements I've taken, only timing is adjusted regardless of frequency cutoff chosen. Even that has a setting now that can be disabled. I can't see how Dirac could be detrimental unless the first measurement is taken wrong.

Well, I sort of agree that a digital signal should survive an extra stage of signal processing, but it clearly doesn't!

I've run DL (the sub 200 Hz version) a number of times and indeed it flattens the bass frequencies, but then if you play a bass-light track that has lots of top-end sparkle through speakers that can deliver this top-end sparkle, you notice that a little is lost when the DL filter is engaged, but it instantly returns when you switch to No Filter. This can be done from your listening chair so easy to test.

When you think about it, engaging a DL filter means the Digital Signal Processor is added to the signal path and any signal processor should ideally be avoided - tone controls, graphic equalisers, loudness filters, DSP, etc - they all do some damage to the precious signal that should be interfered with as little as possible.

To avoid the top end being subjected to DL, you need a system with an active XO and send only the bass to one amp that has DSP and the rest to another amp that has no DSP. In fact the bass drivers in my own speaker system works that way because it is a hybrid system where the bass drivers have their own built-in amp and DSP.

 

[pogo]

top-end sparkle, you notice that a little is lost when the DL filter is engaged

I had a similar problem with my M33 at the beginning. However, the problem disappeared after the FW 3.16.2 upgrade (Dec'21) in the DL implementation section.
The full version of DL could also be helpful for adjusting the treble range.

 

[fcracer]

Well, I sort of agree that a digital signal should survive an extra stage of signal processing, but it clearly doesn't!

I've run DL (the sub 200 Hz version) a number of times and indeed it flattens the bass frequencies, but then if you play a bass-light track that has lots of top-end sparkle through speakers that can deliver this top-end sparkle, you notice that a little is lost when the DL filter is engaged, but it instantly returns when you switch to No Filter. This can be done from your listening chair so easy to test.

When you think about it, engaging a DL filter means the Digital Signal Processor is added to the signal path and any signal processor should ideally be avoided - tone controls, graphic equalisers, loudness filters, DSP, etc - they all do some damage to the precious signal that should be interfered with as little as possible.

To avoid the top end being subjected to DL, you need a system with an active XO and send only the bass to one amp that has DSP and the rest to another amp that has no DSP. In fact the bass drivers in my own speaker system works that way because it is a hybrid system where the bass drivers have their own built-in amp and DSP.

Listening tests from a chair do not tell the full story. You’re likely accustomed to bass that’s excited by a room mode. When DL reduces or eliminates that room mode, it feels like you’ve lost a lot of energy (which you have and it should be that way to correct the frequency curve).

I’d highly recommend downloading REW and taking measurements from your listening position with and without DL. You can use the MMM to capture a lot of measurements in a short period of time. You can then tailor the target curve in DL to your liking.

I like bass so I use the NAD Room Feel curve which boosts bass frequencies to ~+6db and then flattens in the mid frequencies, and then trails off at the high frequencies. This provides a very pleasant listening experience without any fatigue, while still giving some oomph that I enjoy.

I wrote a review for Dirac Live at my non-commercial blog that you may find helpful as it has measurements and before/after: https://fcracer.com/dirac-live-review-digital-room-correction-for-everyone/

Please pay attention to the 47Hz room mode that is adding 12db of energy where it shouldn’t be. When activating DL, it flattens this area, which upon first listen, seems like it’s sucked the bass out of the music. However, if you listen longer, and become accustomed to it, turning DL on again makes the music sound muddy and the bass monotone.

Your concerns about keeping the signal pure I suggest are placing priorities in areas where the return is low. Investing that time and energy into speaker selection, speaker placement and room correction will yield you far greater improvements in sound quality. Dirac Live, has been by far, the best improvement I’ve experienced in my home audio journey thus far. I swear by it.

 

[vddobrev]

Lost track somewhere...but if I remember well, I could hear differences in sound when playing with the app or Dirac, even when I was in "analogue direct mode".
Isn't it that what you are talking about: You are listening to a source in "analogue direct mode" and the sound changes when you engage or disengage a Dirac filter or change the subwoofer settings within in the app?
Nocko!

P.S.: I'll come back to your private message!

Analogue direct is not working on M66 if you have subwoofers.

1. In Analogue direct, subwoofers are playing, and they are not in sync with the main speakers. Dirac is off. Set volume to -40dB and measure with SPL meter.
2. In Analogue direct, press EQ button. Volume is raised by 10dB. As far as I can tell, also the sound is changed, i.e. Dirac Filter is applied. I can live with this, because I did press the EQ button deliberately (my doing), so even though it should not be possible. It should be disabled.
3. Listening to a digital source, like BluOS or Coax in, with Dirac filter enabled. Now switch to Analogue direct - Dirac is not deactivated. I would expect it to be completely off on the Analogue direct source.

But as confirmed by NAD support, M66 does not support audio settings by source, they are applied on the whole device and this is the actual problem.

 

[pogo]

also the sound is changed, i.e. Dirac Filter is applied

Once again, the left and right signals do not pass through the DL filters in Analogue Direct mode. What also happens here is that the full-range signal is sent to the L/R outputs. Of course, NAD should still suppress the output via the sub outputs.

 

[vddobrev]

Once again, the left and right signals do not pass through the DL filters in Analogue Direct mode. What also happens here is that the full-range signal is sent to the L/R outputs. Of course, NAD should still suppress the output via the sub outputs.

OK. It could just be my judgement is influenced by the level change.
I saw the diagram you posted. I can only judge what I am hearing, and I am hearing changed sound.
Analog direct should not be influenced by anything related to Dirac, be it headroom and what not. The Analog direct level should also not change.
If it does, than it means there is no real analog bypass in this device.

 

[pogo]

What you hear is the volume/headroom management of the M66.
A real analog bypass is given in this device.
And of course you will also hear a different sound, as in Analogue Direct mode the left and right output channels are unfiltered (full-range). Take your sub off the mains and listen while switching.

 

[Hear Here]

Your concerns about keeping the signal pure I suggest are placing priorities in areas where the return is low. Investing that time and energy into speaker selection, speaker placement and room correction will yield you far greater improvements in sound quality. Dirac Live, has been by far, the best improvement I’ve experienced in my home audio journey thus far. I swear by it.

Thanks - I'll take a good look at your paper a little later.

However regarding your last paragraph, I agree 100% with your comments about speaker selection, speaker placement and room treatment to minimise the need for any Signal Processing, and indeed my speakers now offer all the quality I want and it must be pretty accurate as switching from DL Filter to No Filter make only a tiny difference in the sound - and no difference to the volume - so DL is actually doing very little.

It is when playing a very bass-light track that I can prove my point about DL doing the top-end no favours, and visitors have also confirmed my finding that a little of the top-end sparkle is lost when a filter is engaged, despite that fact that the version of DL I use is only adjusting sub 500 Hz

 

[vddobrev]

What you hear is the volume/headroom management of the M66

Is that relevant to analogue bypass?

 

[pogo]

This is the current implementation of NAD.
If something bothers you about the implementation, you can make a change request.

 

[vddobrev]

This is the current implementation of NAD.
If something bothers you about the implementation, you can make a change request.

Thank you for the efforts to explain all this.
The current implementaion of NAD is not analgue bypass, it is not pure analogue, regardless what they call it and what schematics they show. There is simply no way that the analogue can be influenced by the digital.
From their data sheet:

So that DSP-enabled functions like Dirac Live are available with all sources, analogue signals are converted to digital by ESS Technology’s flagship ES9822PRO ADC chip. However, users can select the Analogue Direct mode, which bypasses all digital processing. Moreover, the M66 has separate signal paths for analogue and digital sources. Internally, the analogue and digital sections are physically separated and shielded from each other with their own separate power supply sections.

If all of the above were true, then there would have not been any interfernce between digital and analogue.

Edit: From hardware point of view, it may be true. But from software point of view and/or implementation it is not. Simple.

 

[pogo]

The interference results from the common volume management of the M66.
However, this only affects control signals and not the L/R audio signal on the analogue layer.

 

[vddobrev]

The interference results from the common volume management of the M66.
However, this only affects control signals and not the L/R audio signal on the analogue layer.

Yes @pogo I got that.
But what is the user experience?
At one time, the analgue direct set at -40dB volume is playing with a certain SPL.
Then at another time if Dirac EQ is enabled it will be playing with 10dB louder SPL at the same -40dB volume level..
Not to mention the out of sync subs that should not be playing at all.
Oh, and one more thing. When Dirac EQ is enabled, and you switch to Analogue direct Line 1 input, then the subs are in sync!
So no digital processing, right?

BTW, I don't see a NAD M66 in your signature, do you have/had it?

 

[vddobrev]

If something bothers you about the implementation, you can make a change request.

I have filed NAD support tickets for all things I am discussing here. The answer is always the same - we will pass it to our QA/Dev lab for future consideration.
One thing they fixed is "Trigger in" back in Sep-2024, and also enabled AutoSense.
But Trigger in kills the whole M66, including the BluOS section, so you can't trigger in M66 from CD player, and at the same time start it via BluOS streaming. The whole M66 is gone from BluOS if you connect trigger in.
Also AutoSense is not working as it should... If M66 goes in standby by itslef in 15 mins unactivity, then AutoSense does not work on the same input that it was.

So yes, I filed at leaset 7-8 support requests.

 

[pogo]

When Dirac EQ is enabled, and you switch to Analogue direct Line 1 input, then the subs are in sync!

In this case, switch back and forth between Analog direct Line 1 and Analog Line 1.
If the subs are really in sync, the stereo signals L/R are not played back via the analog path.

 

[vddobrev]

In this case, switch back and forth between Analog direct Line 1 and Analog Line 1

I am not getting this, elaborate please. So is this yet another bug?

 

[pogo]

Maybe a control signal bug.

 

[Nocko!]

@all:
Just for my understanding, I gave my M66 back before evaluating this to the end:
If you listen to music with "analog direct" switched on and there are no subwoofers in the system: Does the sound change when you
a) switch on / off Dirac?
b) change the Dirac preset?
c) change the crossover settings?
d) activate a subwoofer output within the BluOS app?

But on the other hand - this is to no avail: If you have a setup with subwoofers and the subwoofers do strange things when "analog direct" is engaged, then there is no "analog direct" but a faulty construction.
Nocko!

 

[vddobrev]

@all:
Just for my understanding, I gave my M66 back before evaluating this to the end:
If you listen to music with "analog direct" switched on and there are no subwoofers in the system: Does the sound change when you
a) switch on / off Dirac?
b) change the Dirac preset?
c) change the crossover settings?
d) activate a subwoofer output within the BluOS app?

But on the other hand - this is to no avail: If you have a setup with subwoofers and the subwoofers do strange things when "analog direct" is engaged, then there is no "analog direct" but a faulty construction.
Nocko!

I will try all this out of curiosity and report back.
But last time I tried point d) activate a subwoofer output within the BluOS app... there was such a loud pop from my speakers, that I most likely will not try again.