Review and Measurements of NAD T758 V3 AVR

[Dj7675]

I don’t think he said that at all.

Hopefully @amirm will correct what I thought I understood!

 

[amirm]

Hopefully @amirm will correct what I thought I understood!

You understood well.

 

[Theriverlethe]

We use psychoacoustics so that we don't have to run out and perform double blind tests every minute. I explained why perceptual masking does not help you here. You can't counter that with "I don't think so" and demand a double-blind test.

Look at this graph:

That high distortion goes way down to 20 Hz as it should since the circuit is operating well outside of its design metrics (due to amp clipping). So -now take that 1 kHz tone and move it down in frequency such that those harmonics land in 2 to 5 kHz. Then look at Fletcher-Munson curves:

See how the thresholds for hearing anything there is actually negative SPL? And therefore way way lower than the harmonics we are seeing here?

Those harmonics keep going higher where the amplitude of content is very low. It mixes with them and potentially makes them higher pitched.

So your skepticism is not based what we have measured and what we know about science of what we hear.

I’m aware of Fletcher-Munson type curves. I’m not aware of any research that shows audibility of 0.25% distortion.

 

[amirm]

I’m aware of Fletcher-Munson type curves. I’m not aware of any research that shows audibility of 0.25% distortion.

There is no such thing as "audibility of 0.25% distortion." THD+N is not instructive that way because it is a single number. This is why I show the spectrum. You use that to perform the analysis that I showed you to determine audibility.

 

[GrimSurfer]

So you know then that the range of human hearing range should from 0-120 dB?

 

[Theriverlethe]

So you know then that the range of human hearing range should from 0-120 dB?

Sure, humans can hear below zero decibels in absolute silence. You won’t hear a mosquito next to a jet engine.

 

[GrimSurfer]

There is no such thing as "audibility of 0.25% distortion." THD+N is not instructive that way because it is a single number. This is why I show the spectrum. You use that to perform the analysis that I showed you to determine audibility.

I was going to walk him through it, @amirm. I'll first confirm his understanding of F-M. Then I'll introduce him to even/odd order harmonics. Next, I'll convert 0.25% THD to -54 dB. Then I will show him what that means against a primary frequency (or series of frequencies) played at reference levels. I will then explain the limits of masking. Next I will superimpose spls on the F-M curves.

He'll sense the trap when I get to the part about reference levels and start to deny the validity of science, his super human hearing, the brain's marvellous and medically unexplained ability to be a notch filter into to Tetrahertz range, etc.

He'll then say I'm insulting him, trying to embarrass him, and am a rude and ignorant twit. He'll be joined by other surrealists, subjectivists and anyone who has taken exception with anything I've ever said (including grammatical errors and typos).

Having mapped out all of that, what do you say about leaving him to figure it out on his own?

@Theriverlethe: You're on your own.

 

[audimus]

I was going to walk him through it, @amirm. I'll first confirm his understanding of F-M. Then I'll introduce him to even/odd order harmonics. Next, I'll convert 0.25% THD to -54 dB. Then I will show him what that means against a primary frequency (or series of frequencies) played at reference levels. I will then explain the limits of masking. Next I will superimpose spls on the F-M curves.

It would very useful if someone did this explanation that fit together X different metrics - absolute and ratios - thrown about into a coherent, self-explanatory description and relate it to audibility. Not to spite someone but I suspect a vast majority of the readers here don’t have a clue of what all this means even if they agree with the conclusion.

Such a thing, placed in a FAQ or a community Wiki could be very useful to newcomers as well.

 

[Theriverlethe]

I was going to walk him through it, @amirm. I'll first confirm his understanding of F-M. Then I'll introduce him to even/odd order harmonics. Next, I'll convert 0.25% THD to -54 dB. Then I will show him what that means against a primary frequency (or series of frequencies) played at reference levels. I will then explain the limits of masking. Next I will superimpose spls on the F-M curves.

He'll sense the trap when I get to the part about reference levels and start to deny the validity of science, his super human hearing, the brain's marvellous and medically unexplained ability to be a notch filter into to Tetrahertz range, etc.

He'll then say I'm insulting him, trying to embarrass him, and am a rude and ignorant twit. He'll be joined by other surrealists, subjectivists and anyone who has taken exception with anything I've ever said (including grammatical errors and typos).

Having mapped out all of that, what do you say about leaving him to figure it out on his own?

@Theriverlethe: You're on your own.

Well, -52dB is how I got to 0.25%

 

[Theriverlethe]

I was going to walk him through it, @amirm. I'll first confirm his understanding of F-M. Then I'll introduce him to even/odd order harmonics. Next, I'll convert 0.25% THD to -54 dB. Then I will show him what that means against a primary frequency (or series of frequencies) played at reference levels. I will then explain the limits of masking. Next I will superimpose spls on the F-M curves.

He'll sense the trap when I get to the part about reference levels and start to deny the validity of science, his super human hearing, the brain's marvellous and medically unexplained ability to be a notch filter into to Tetrahertz range, etc.

He'll then say I'm insulting him, trying to embarrass him, and am a rude and ignorant twit. He'll be joined by other surrealists, subjectivists and anyone who has taken exception with anything I've ever said (including grammatical errors and typos).

Having mapped out all of that, what do you say about leaving him to figure it out on his own?

@Theriverlethe: You're on your own.

With THX reference peaks at 105dB, that puts the third harmonic at 53dB, below the noise floor of most rooms. Of course, noise below the room’s noise floor could still be audible, were it not for the fundamental peak more than 32 times louder.

 

[GrimSurfer]

With THX reference peaks at 105dB, that puts the third harmonic at 53dB, below the noise floor of most rooms. Of course, noise below the room’s noise floor could still be audible, were it not for the fundamental peak more than 32 times louder.

53 dB or higher noise floor? Are you living in a bus station?

 

[amirm]

With THX reference peaks at 105dB, that puts the third harmonic at 53dB, below the noise floor of most rooms.

No room has "53 dB" of noise. That is what a dumb SPL meter shows. The actual noise in the room is heavily biased to low frequencies because those are the ones that walls don't block easily. In mid-levels where our hearing is most sensitive, many rooms come close to threshold of hearing. See this article I wrote for WSR magazine and please don't keep repeating this myth: https://www.audiosciencereview.com/forum/index.php?threads/dynamic-range-how-quiet-is-quiet.14/

As you see, the best rooms surveyed are actually much quieter then threshold of hearing as it should be. Go into a room and close the door. Do you hear anything? If not, the noise can't be 53 dB. Sometimes you need to "trust your ears" and nowhere that is more important than acoustics....

 

[GrimSurfer]

And btw, @Theriverlethe, you're presenting an incorrect view of the sound levels too. It's not 105 dB peak, it's 85 dB that you should be using. That's the spl that is predominant (mode or mean) when listening at reference levels.

 

[Theriverlethe]

And btw, @Theriverlethe, you're presenting an incorrect view of the sound levels too. It's not 105 dB peak, it's 85 dB that you should be using. That's the spl that is predominant (mode or mean) when listening at reference levels.

Yes, but the clipping only comes into play with a full scale signal like Amir’s test tone.

 

[GrimSurfer]

It would very useful if someone did this explanation that fit together X different metrics - absolute and ratios - thrown about into a coherent, self-explanatory description and relate it to audibility. Not to spite someone but I suspect a vast majority of the readers here don’t have a clue of what all this means even if they agree with the conclusion.

Such a thing, placed in a FAQ or a community Wiki could be very useful to newcomers as well.

Maybe. But for the moment it seems to me that @Theriverlethe is trolling. Why do I think this?

He joins the forum yesterday. Then opens his posts claiming that the poor performance of the T758 is irrelevant. Then he starts laying out a flawed thesis that makes some of the right noises which might otherwise fool readers. He then tries to engage @amirm, probably to draw him into a slanging match. Amir doesn't take the bait, so @Theriverlethe, then starts to play dumb.

When that doesn't work, he sets forth on another tangent that is technically weak. Somebody who didn't know what they were talking about would make a gross error or cock up terminology.

Either @Theriverlethe wants to undermine the thrust of the review, either for business or personal reasons. This is not science or scientific interest. It's trolling.

 

[amirm]

Yes, but the clipping only comes into play with a full scale signal like Amir’s test tone.

Full amplitude content is quite common and has been since loudness wars started. It is routine to get content at 0 dB.

 

[amirm]

Maybe. But for the moment it seems to me that @Theriverlethe is trolling. Why do I think this?

I don't think he is trolling. He has the unit and is defending it.

 

[GrimSurfer]

I don't think he is trolling. He has the unit and is defending it.

Oh... another one of "those".

This is as tedious as trolling. Ha ha.

I guess that's the difference between the mature and immature audiophile. The mature audiophile accepts that their components may not be ideal but are committed to learning what they can to do it better the next time.

The immature audiophile considers their system unassailable because they believe it is a reflection on them. Until they tire of it and get trapped into a never ending circle of confusion. The consumer electronics industry loves such people.

 

[amirm]

Oh... another one of "those".

This is as tedious as trolling. Ha ha.

Gives us a chance to dig into the topic a bit so not entirely bad.

 

[GrimSurfer]

Gives us a chance to dig into the topic a bit so not entirely bad.

True. But these discussions never seem go anywhere because the most technically accurate conclusion is that which the subject cannot accept in the first place.

For @Theriverlethe: If you're here to learn, stick around. There are many ppl brighter than me who can expand your knowledge of audio.

If you're only here because you disagree with the technical assessment of the T758, so be it. Declare that as your purpose and move forward from there. But I'd advise you to have a good grip on the basics or you'll be shut down time and time again by people who know wthat they're talking about. [I'm no expert and exhibit, on good days, only average intelligence but could spot the flaws in your argument without much difficulty.]

Start with asking an open and honest question: I'm trying to understand how a THD of -54 dB could be audible. Could someone explain? People like @amirm, @Blumlein 88, @SIY, @DonH56 will jump in an explain in ways that will change your understanding of audio forever.