NAD M33 Streaming Amplifier Review

[SIY]

Where can I find it?

July issue of AudioXpress.

 

[pogo]

If I was only listening with main speakers I would be perfectly happy with the M33.

But even this is no guarantee for a distortion-free reproduction!:
'Clipping bug confirmed by NAD engineers. Bug limited to only those who use subwoofer and never run Dirac live or use Dirac filters with too levels too high.'

In my case, the second case occurs with main speakers only. I had already uploaded an sound example in this thread.

 

[Stefan]

use Dirac filters with too levels too high.'

In my case, the second case occurs with main speakers only. I had already uploaded an sound example in this thread.

I totally believe you, but I have tried this on levels that almost hurt my ears way above levels I usually use and can not hear it (DL ON, Sub OFF). So practically that is not the main issue for me.

 

[KjetilA]

'Clipping bug confirmed by NAD engineers. Bug limited to only those who use subwoofer and never run Dirac live or use Dirac filters with too levels too high.'

What level are we talking about here? Volume, or that you have set the target too high in dirac?

 

[pogo]

Normal output volume.

See also here: Link

 

[Kal Rubinson]

Admittedly, I do not listen to ultra-compressed pop.

The unit I had was the same one @Kal Rubinson used for his review. He also apparently never ran into a distortion problem. Just to put things in perspective.

Yup and I don't listen to ultra-compressed pop either.

 

[pogo]

Yup and I don't listen to ultra-compressed pop either.

Ultra-compressed pop does not seem to be the only trigger for distortions. There is also the second case: 'use Dirac filters with too levels too high'
NAD will probably have to retune/rethink the entire signal chain, including all internal interfaces (and there are quite a few) and taking into account the BluOS restrictions. Not an easy task...

 

[jaymusic]

Found this thread after searching for opinions on the M33, having bought one about a month ago.
I listened to the Lana Del Rey track 'For Free' and can confirm I also heard the clipping ... sound like a crackling on the word 'walking' a minute or so into the track.
Using Sonus Faber Sonetto II speakers and a single Sonus Faber Gravito I subwoofer. 80hz crossover, sub volume at about 60%. Using the full version of Dirac Live with a profile created including the sub.
I added -1db headroom adjustment in Roon and it went away. I only use Roon so it's a solution for me and has no real impact that I can hear on the volume or general sound of the music, but appreciate for those not using Roon it's not great.
I don't like using the Tone Controls on the M33. Dirac already reduces volume so an additional 6db volume reduction if using Tone controls means I need to have volume set at -20db to play at the level I like.

Have to say that in most cases the M33 sounds brilliant, but can show up poor recordings.

 

[Stefan]

I added -1db headroom adjustment in Roon and it went away. I only use Roon so it's a solution for me and has no real impact that I can hear on the volume or general sound of the music, but appreciate for those not using Roon it's not great.

This is pretty interesteing as I have been contemplating about Roon for some time now. What is the technical background of this, so Roon can pre-process tracks in a way that it generates more headroom? And this is not compromising the audio data?

 

[jaymusic]

This is pretty interesteing as I have been contemplating about Roon for some time now. What is the technical background of this, so Roon can pre-process tracks in a way that it generates more headroom? And this is not compromising the audio data?

Roon has a full DSP engine... Headroom management, Sample rate conversion, procedural and parametric EQ, convolution, crossfeed and speaker set up.
I've played around with the upscaling and headroom, but use it all pretty sparingly.
With headroom adjustment, I have used only 1db. Does it affect the quality? I don;t know - I can;t really hear any difference other than the removal of the clipping sound that has been discussed.

DSP Engine: Headroom Management (roonlabs.com)

 

[Stefan]

Thank you very much for the link. So Roon states that

"Headroom Management is at the top of the list because it's one of the most important things to pay attention to in Roon's DSP Engine. If things don't sound right, one of the first things you should do is make sure that the signal isn't clipping."

but NAD obviously dismissed this in their DSP programming?

So there could technically be a fix after all?

 

[jaymusic]

Thank you very much for the link. So Roon states that

"Headroom Management is at the top of the list because it's one of the most important things to pay attention to in Roon's DSP Engine. If things don't sound right, one of the first things you should do is make sure that the signal isn't clipping."

but NAD obviously dismissed this in their DSP programming?

So there could technically be a fix after all?

Well, in that respect there already is a solution with M33. I believe that switching on Tone controls drops the dB's by 6 across the frequency spectrum, which you can alter to just dropping by 1db with separate adjustments for treble and bass. But it's very basic compared to Roon and for some reason when doing this in the M33 I think the sound quality takes a hit (something that doesn't seem apparent when just using a small headroom adjustment in Roon).

Here's the signal chain on a track showing the headroom adjustment prior to sending to the M33.

 

[Stefan]

This has been discussed some pages ago with some variance:

Hello Rene,

Thank you for your reply.

This issue is a high priority on the engineering team's list to resolve but not a simple fix, hence it has taken longer than expected to resolve.

The distortion does not affect all tracks, just a few that were recorded HOT with inter-sample clipping.

The distortion can be resolved by setting "Tone Controls - ON", or if one does not have subwoofers connected, setting "Select Attached Speakers - No Subwoofer".

Again I apologize that we do not have a more immediate solution for you now, but we will let you know when a fix is released.

Kind Regards,

Bob Moran
NAD Support Specialist

This reply from NAD support doesn't help at all, because setting "Select Attached Speakers - No Subwoofer" eliminates the problem anyway.

You are right Kaboo. The more I listen, especially with headphones (with Dirac off, obviously) I realize it was not just a reduction in decibels with Tone Controls on, it flattens the soundstage a bit. I mean, at least I think so, it's hard to tell if it is just the -6db affecting my perception or not. It's not dramatic, but the loss of dynamics seems to be there.

It's just your perception being affected by the significant 6 dB drop in output level. If you increase the output level by 6 dB using the volume control, then you should perceive that the soundstage will unflatten back to its original state. Our ears are nonlinear in their frequency response with respect to sound level, so a 6 dB change elicits a large subjective change in sound quality.

I for myself am with Thalassophile. By extensive listening I can also hear that adjusting the volume by +6 dB after switching TONE CONTROL ON is definitely altering the sound and not to the better side. So the M33 works differently to Roon shown above.

 

[jaymusic]

So all of a sudden the crackling on Lana Del Rey's track mentioned in this thread is gone.
I switched off my Roon headroom adjustment as I wanted to tweak it to the least adjustment possible to get the crackling to stop. Roon can adjust in small fractions of a dB... I got down to -0.05dB headroom adjustment and no crackling sound, so I just turned headroom off to make sure the crackling was still apparent - and it was not. It's literally gone.

The only thing that has changed since yesterday is that I switched the M33 off and replaced the power chord with a shielded one from Chord (which of course should have nothing to do with it).

Baffled.
I will probably just leave Roon headroom adjustment on at -0.05dB.

 

[pogo]

The only thing that has changed since yesterday is that I switched the M33 off and replaced the power chord with a shielded one from Chord (which of course should have nothing to do with it).

Please make a cross check with the old power chord. Possibly also plug in the connector differently (180° rotated), depending on the country.

 

[EB1000]

So all of a sudden the crackling on Lana Del Rey's track mentioned in this thread is gone.
I switched off my Roon headroom adjustment as I wanted to tweak it to the least adjustment possible to get the crackling to stop. Roon can adjust in small fractions of a dB... I got down to -0.05dB headroom adjustment and no crackling sound, so I just turned headroom off to make sure the crackling was still apparent - and it was not. It's literally gone.

The only thing that has changed since yesterday is that I switched the M33 off and replaced the power chord with a shielded one from Chord (which of course should have nothing to do with it).

Baffled.
I will probably just leave Roon headroom adjustment on at -0.05dB.

Are you also using Roon's level adjustment? That alone will eliminate the clipping distortion, since it will reduce about -6dB on all tracks on average

 

[jaymusic]

Are you also using Roon's level adjustment? That alone will eliminate the clipping distortion, since it will reduce about -6dB on all tracks on average

No, I don't use the levelling adjustment (though I did check it wasn't on as I have played around with it in the past, never to my liking. It was not on).

With no pre-processing in Roon of the audio signal at all, the crackling sound is gone. It WAS there yesterday and very clearly there.
I really haven't done anything other than turn the unit off for the first time in a few weeks to replace the power chord with an expensive one (that probably makes no difference )

 

[jaymusic]

Please make a cross check with the old power chord. Possibly also plug in the connector differently (180° rotated), depending on the country.

I will check later with the old power chord again - it's a 3 pin plug so only one way to connect (UK).

 

[The Real Gabriel]

The only thing that has changed since yesterday is that I switched the M33 off and replaced the power chord with a shielded one from Chord

Here we go.

 

[jaymusic]

Here we go.

Just to be clear, no claim from me it's the power chord. I really don't believe that for a second. Can't think of any logical reason, but it is the only change - other than just the fact the unit was turned off and on again.