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

[MingChops]

i contacted eversolo trying to find out more about how they implement digital volume control , here is what the answered:

Digital Volume Control (DVC) achieves volume control by adjusting the amplitude of the digital audio signal instead of adjusting voltage through analog circuits. Digital volume is adjusted through registers inside the DAC. This adjustment process does not reduce the bit depth of the digital audio signal, as it only adjusts the amplitude of the signal without altering the original encoding of the signal.
In short, digital volume control does not result in a decrease in bit depth because it simply controls volume by modifying the amplitude of the digital audio signal rather than altering the signal's encoding. Therefore, even with volume adjustments, the integrity and quality of the digital audio signal remain unchanged.

Right, so they're right technically - but it's a little bit of semantics as the end result is still the same, which is a degradation of audio that is more pronounced the more attenuation you need to apply digitally. I mistakenly (like I guess many) thought it was bit rate reduction, but the net effect of using DVC on digital amplitude still reduces dynamic range and SNR, but 'techincally' yes.... it's not via a bit rate reduction.

End of the day, this is why they went to the expense and effort to do the resistor ladder volume in the A8.

I had to run it past ChatGPT to confirm something and got the answer I was looking for:

You:
does digital volume control in audio reduce the bit rate?

ChatGPT:
Digital volume control in audio typically does not directly reduce the bit rate of the audio signal itself. Bit rate refers to the amount of data processed per unit of time and is primarily affected by factors such as sample rate and bit depth.
When you adjust the volume digitally, what typically happens is that the digital audio signal is scaled up or down in amplitude before being converted to an analog signal for playback. This scaling process does not inherently reduce the bit rate because it doesn't involve removing any data from the audio signal.
However, there can be some indirect effects on perceived audio quality. If the volume is reduced significantly, the signal-to-noise ratio (SNR) can be adversely affected, resulting in audible quantization noise. This noise is a byproduct of the digital-to-analog conversion process, and while it doesn't directly reduce the bit rate, it can affect perceived audio quality, particularly at lower volume levels.
In some cases, digital volume control can also introduce distortion or artifacts, especially when reducing the volume, although modern audio processing techniques aim to minimize these effects.
Overall, while digital volume control doesn't directly reduce the bit rate of the audio signal, it can affect perceived audio quality in various ways.

You:
sounds strange. I thought a digital audio signal was 0's and 1's, and within that signal is the encoded audio samples, which dictate the volume for decoding. for example a 16 bit track has a maximum amplitude value of 65536, how does reducing the digital signal amplitude change what the dac ultimately decodes from the audio?

ChatGPT:
You're correct that a digital audio signal consists of a sequence of binary values representing audio samples. Each sample has a certain bit depth, which determines the resolution of the sample's amplitude. In a 16-bit audio system, as you mentioned, there are 65,536 possible amplitude levels.
When you adjust the volume digitally, you're essentially scaling the amplitude of each sample before it is converted from digital to analog form by the DAC (Digital-to-Analog Converter). This scaling process doesn't directly change the bit rate of the audio signal because the number of bits representing each sample remains the same.
However, reducing the amplitude digitally effectively reduces the dynamic range of the audio signal. Dynamic range refers to the difference between the loudest and softest sounds in the audio signal. If you reduce the volume digitally, you're essentially reducing the amplitude range within which the audio signal is encoded. This can result in a loss of detail, particularly in quieter parts of the audio signal.
Additionally, if the volume reduction is significant, it may cause the least significant bits (LSBs) of the audio samples to be truncated or rounded off during the scaling process. This can introduce quantization noise, which may become audible, especially in quieter passages of the audio.
So, while adjusting the volume digitally doesn't directly change the bit rate of the audio signal, it can affect the perceived audio quality due to changes in dynamic range and the potential introduction of quantization noise.

I'm not an engineer, but this makes sense to me, confirms the issues, and is well articulated I think - I love ChatGPT!

 

[Cpopovic]

A firmware update seems to be out but it is not for the M66

https://support.bluos.net/hc/en-us/articles/4415227249175-Introducing-BluOS-4-2-10

 

[pogo]

Have you carried out the update and which third digit is now displayed?

 

[Cpopovic]

Have you carried out the update and which third digit is now displayed?

BluOs 4.2.105

 

[pogo]

 

[sabloke]

Great, another infomercial... This lack of decent reviews is puzzling.

 

[pogo]

It even seems to be possible to use an external DAC via USB. But why should you do that?

 

[Waxx]

I looked at it, but i still don't see why this, on it's own a very good preamplifier probally (if we can rely on the NAD reputation), would be worth a lot more than a MiniDSP SHD. It got less sub output possibilities, but it's only 1300€ for proven high quality, roon ready and with a full dirac possibility. It does not have a phono stage, but for a few hundreds a top levle (Cambridge) one is added to the analog input. And if you don't need the streaming (like i), even a minidsp flex is as good.

If they would halve the price, it would be justified, but not for 5K (or even more on this side of the pond). Not even with the NAD badge on it and if it would measure in the top league on specs.

 

[markrubin]

I decided to keep the M66 since the ROON issue got fixed: my next step is to sell my M50.2 and install the M66 in the rack. I also decided at age 76 I must stop being an early adopter of new, unfinished products….

 

[GXAlan]

I looked at it, but i still don't see why this, on it's own a very good preamplifier probally (if we can rely on the NAD reputation), would be worth a lot more than a MiniDSP SHD.

1) Dirac Live Bass Control
2) Dirac Active Room Treatment

The better question is if this is better than a Monolith HTP-1 which also promises Dirac ART and ships today with DLBC support.

 

[pogo]

...and DL processing @192kHz

 

[rlarson]

I'm new to Roon and have the NAD M66. I could enable Roon and play through the BLUOS app on my smartphone or computer.


Also just realized it looks to be playing through Airplay, not sure what sound quality effect this will have

 

[markrubin]

^
ROON will give you the best sound quality, and the response is much faster
ROON has the update that will allow the M66 to be recognized as Ready/Tested
if you do this: in the ROON app, you should disable the Airplay connection first, then enable the ROON ready selection

 

[rlarson]

^
ROON will give you the best sound quality, and the response is much faster
ROON has the update that will allow the M66 to be recognized as Ready/Tested
if you do this: in the ROON app, you should disable the Airplay connection first, then enable the ROON ready selection

Bingo, Thank You

 

[Hear Here]

I decided to keep the M66 since the ROON issue got fixed: my next step is to sell my M50.2 and install the M66 in the rack. I also decided at age 76 I must stop being an early adopter of new, unfinished products….

Why sell the M50.2? It duplicates nothing with the M66 apart from the streamer feature. The M50.2 will PLAY a CD, it will RIP a CD, it will STORE the digital files of a CD on its twin hard drives. The M66 does none of these. But perhaps you are ditching hard media and relying totally on streaming services such as Qobuz. I'm inclined to agree, but for the time being, I'm keeping my M50.2, even though I get 90% of my music from my M33. This won't change if and when I go for the M66.

Thanks

 

[pogo]

Contrary to the manual, it should be possible to switch through the DL presets using the EQ button on the SRM1.

This function is now described in the new manual from March. We are slowly approaching the level of an M33

 

[Fidji]

From my point of view, waveforming is a generation behind. The M66 should also get DLART this year. That will also be unbeatable with 2.0 setups. Waveforming doesn't work here and DLART is preferable in smaller 2.x setups in the living room!

WF is designed to serve a very specific market of purpose-built high-end home theatres - to be the best. You can still get very respectable results with an imperfect setup, but there are some minimum requirements that need to be met. So, as you rightly point out, DLART will be much more usable for standard living room/simple HT setups, or even high-performance HT with, say, 2 large subs up front.

As you can see from my signature, I am a current Trinnov owner and one of the participants in the early access WF release, including the latest Pressurisation feature [special way of handling frequencies below 1st mode]. So read whatever bias in my statements.

Had a chance to compare my [9.8.7] WF with very high quality DLART Perlisten/StormAudio 9.4.4 setup [4 sub upfront placement, in similar room size] - both rooms professionally treated. Cost of both setups was +- the same, subs only were more expensive in Perlisten rig. Woofage/Wattage advantage on Trinnov [mine] rig side.

Anecdotical, as it goes - WF worked much better, for both HT and music. Consensus of 2 owners [mine and the Perlisten guy] + our common friend, that enabled the whole comparison. Of course we are comparing it in "Ferrari vs Porsche" realm.

Also - from his experience - DLART seems to work best in proper condition, and really benefits from adding subs/speakers. Also Bass Reflex seems not to be a best friend of DLART [he is using his in Acoustic Suspension mode]. He actually prefers 2.2 setup with each sub corrected individually [making his fronts 4 way speaker] for music listening. DLART for Movies/MCH.

So I would tame your expectation - if you install DLART in untreated room with 2 bookshelf speakers, probably will work better than nothing, but it will still sound like 2 bookshelf speakers in untreated room. I can see the same hype building, as couple of years ago re DLBC, which prooved to be rather underdelivering vs initial expectations.

So no WF is nothing like "generation behind" it is just meant for different use case. Trinnov [obviously] get lot of questions re DLART - and their response is - WF prevents the problem, DLART mitigates the consequences. THis is a good summary

Trinnov Reveals Details of WaveForming Redefines Low Frequency Reproduction

Trinnov’s new WaveForming technology seems remarkably similar in capabilities to DIRAC ART. This editorial illustrates the differences and how to plan your speaker and subwoofer system accordingly.

www.audioholics.com

What was it that made you opt for the Nova in the end? Do you know if the Nova will get Waveforming?

Do not think so - it's user base would be extremely limited [as you need 4 subs minimum for WF]

 

[pogo]

Of course, ART (co-optimization) has advantages and, in my point of view, is already a generation ahead. In the automotive sector, the co-optimization is already taking place in the kHz range. I wouldn't compare WF with a STORM and ART because STORM only processes at 48kHz. Here you have to wait for the big High-End players like NAD with 192kHz, .... A good ART setup consists of potent full-range speakers. That has to be understood first.

 

[MingChops]

High-End players like NAD with 192kHz

What are your thoughts about the fact Dirac on the NAD is ’only’ 32bit? I’m genuinely not sure if this poses a problem or not, but wonder if it could have an impact on the dynamic range and SNR (same type of issues with many digital volume controls) at lower volumes?

I’m noting that NAD’s previous M12 digital volume implementation used 62bit DSP and was capable of 35bit accuracy (according to their product blurb). So 32bit DSP processing in the M66 seems comparatively low?

The SqueezeDSP implementation I’m currently using runs at 64bit also, and I don’t notice any degradation using it (only the net benefits that PEQ provides). But if halving that processing accuracy as would be the case on the M66, then possibly that might have an impact, especially at lower volumes where digital volume tends to struggle?

(This is why I was hoping the M66 used it’s resistor ladder volume for everything, and not just analogue bypass!).

 

[Fidji]

Of course, ART (co-optimization) has advantages and, in my point of view, is already a generation ahead. In the automotive sector, the co-optimization is already taking place in the kHz range. I wouldn't compare WF with a STORM and ART because STORM only processes at 48kHz. Here you have to wait for the big High-End players like NAD with 192kHz, .... A good ART setup consists of potent full-range speakers. That has to be understood first.

Re Storm - this is the only real-life implementation now, as far as I know. I just wanted to offer real-life experience. That's all. I have no other stake in this discussion.

NAD is not on my radar - I do not need BlueSound Node in nice case [which is basically what M66 is], I get similar functionality our of my Linns. Also their Power Amps range [as I understand, they have abandoned any own R&D, and now act as any other Purifi module assembler] is not offering any advantage over e.g. Audiophonics or Buckeye.

Anyway, NAD is also meaningless here in the greater scheme of things -years of mediocre offerings in AVP/AVR has taken its toll on their brand reputation, unfortunately. Which is a pity, because it used to be nice unassuming good value for money brand. They are too small now to make any impact on anything.

It is the big boys like HarmanKardon or Denon/Marantz and their implementation of DLART that will define its success. I am much more curious about how HK [JBL] will approach it - as they have both Dirac [in form of re-badged Arcams] and re-badged Trinnov [top level AVP] in their current offer.