An alternative Amplifier THD plot

[Omid]

That's correct but you need to note that SINADs above 100 dB routinely are dominated by noise, not distortion. Noise you can hear in absence of music. Distortion is not the same. Noise also combines when you have more speakers.

As to your OP, multiple people have reached out to me about it and my answer is the same as @NTK. It is not an argument that can be made with straight face. It is unlike John to have come up with this as his other papers make plausible cases for high fidelity.

Thanks for your answer, I thought the graph had merit (but point well taken that the other amplifiers in the white paper are more than adequate as well).

 

[solderdude]

The Benchmark paper is 'advertising material'.
Don't get me wrong... the stuff they make is great and the tutorials/info they provide is usually correct but... this article is marketing.

One should keep in mind that the dynamic range of humans when listening to music is about 60-70dB.
Quiet passages and a pause between songs is where one gets to hear background noises such as the dishwasher, traffic outside, airco etc.
You won't be aware when playing music at very loud levels so the 'distortion to dishwasher' comparison is problematic.

Also .... average weighted noise levels (as used in the paper) differ from the dynamic behavior of music.

 

[Omid]

The Benchmark paper is 'advertising material'.
Don't get me wrong... the stuff they make is great and the tutorials/info they provide is usually correct but... this article is marketing.

One should keep in mind that the dynamic range of humans when listening to music is about 60-70dB.
Quiet passages and a pause between songs is where one gets to hear background noises such as the dishwasher, traffic outside, airco etc.
You won't be aware when playing music at very loud levels so the 'distortion to dishwasher' comparison is problematic.

Also .... average weighted noise levels (as used in the paper) differ from the dynamic behavior of music.

I must say that with my little HTML file I created, I could not hear white noise below -68 dB compared to the signal. So what you’re saying makes complete sense.

 

[solderdude]

I used this device I made (about 35 years ago) to determine that value.

With it I can instantly apply a specific attenuation.
I was interested in my own audibility thresholds at that time and had a 4-deck 20 position rotary switch floating about and made that device.
When playing music quite loud (I reckon 105dB peaks or so) and then switching to a certain attenuation I found that when attenuating music -70dB I heard nothing any more.
With continuous test tones this number was bigger (can't remember the value).
So ... when listening to music then (non continuous) sounds -70dB (equivalent to 0.03% distortion that is not masked) seem inaudible to me.

 

[MaxwellsEq]

John Siau (@John_Siau Benchmark media) recently posted this post suggesting a more useful way of representing the performance of an amp. A graph of THD+N vs in room loudness is offers a practical way to judge an amp compared to the standard THD+N vs power plot (using the same data). He explains it very well in his post here, on benchmarkmedia's website. Amir (@amirm) if you read this, I'm wondering if you might still have the data used to generate your THD+N vs Measured W plots. If so it'd be possible to create a series of charts plotting 'THD+N vs in room loudness' for all previously measured amps, making comparisons across their whole power range easier.
To be clear I'm not suggesting changing any past or future reviews. If the data is available, I'd be happy to try create these new graphs, and post them here as another useful way to review and compare amps.

When I started in electronic engineering, FFT was a pipedream. It was years before I experienced a noise-per-frequency plot. The problem is that this technology, while very useful, has now made us misunderstand noise.

A lot of noise has a random, time-specific character - by that I mean, if you were to look at noise from an amplifier or in a room at exactly 2 kHz, a million times a second, each value would be different and the variation would be large (the needle would swing around a lot). What we see with an FFT view of noise against frequency is the average value in a bucket at that time. It looks solid, concrete. This is one of the reasons that noise measured to be X at an "average value", does not always mask signals below it. We effectively "hear through the noise floor".

 

[Omid]

When I started in electronic engineering, FFT was a pipedream. It was years before I experienced a noise-per-frequency plot. The problem is that this technology, while very useful, has now made us misunderstand noise.

A lot of noise has a random, time-specific character - by that I mean, if you were to look at noise from an amplifier or in a room at exactly 2 kHz, a million times a second, each value would be different and the variation would be large (the needle would swing around a lot). What we see with an FFT view of noise against frequency is the average value in a bucket at that time. It looks solid, concrete. This is one of the reasons that noise measured to be X at an "average value", does not always mask signals below it. We effectively "hear through the noise floor".

That’s an interesting insight. And easy to verify. When I played a white noise and played a test tone I could still hear it although it was 30dB below the noise floor.
Conversely, When I played a loud tone at ~600hz I could hear white noise that was 68dB less loud (but barely). So a single tone is a much less effective masker.

 

[Omid]

So with all of this said, what’s a sufficient Sinad for an amp? We can’t perceive noise 70 dB below the music. Each time we double noise, we increase loudness by 3dB. So if there are 3 components in the chain (DAC, preamp, amp) we want another 9dB as a margin of safety. So if the amp’s SINAD is roughly 80dB below sound level, it should be good enough? Or am I missing something?

 

[MaxwellsEq]

So with all of this said, what’s a sufficient Sinad for an amp? We can’t perceive noise 70 dB below the music. Each time we double noise, we increase loudness by 3dB. So if there are 3 components in the chain (DAC, preamp, amp) we want another 9dB as a margin of safety. So if the amp’s SINAD is roughly 80dB below sound level, it should be good enough? Or am I missing something?

Good noise behaviour is an indication of engineering competency. It's a sign that care has been taken over signal routing, screening, PSU design and mains-noise rejection etc.

What this lab-confirmed care and attention also means is that the kit is more likely to still have low noise in a domestic environment with noisy mains, or heavy RF exposure. An amplifier that struggles to get noise in the lab down to -70 dB, may well struggle even worse in a poor domestic environment. So, if there's an amplifier with noise at -90 dB I'd pick that over a -70dB amplifier.