What is the "ground/floor noise" oft refered to here?

How does it manifest itself?

 

Firstly, the terminology is incorrect. It's "noise floor" ; not "floor noise". It's the amount of noise you hear when no music is playing and/or during extremely quiet passages of music.

"Ground noise" is something entirely different and is a buzzing/humming sound one will hear if there is a grounding issue.

 

There is a pretty in-depth discussion about it here.

 

I am not quite sure of the exact context that you are asking this question; however, I suspect that you are referring to the noise floor in the average listening room.

In the average listening room in the average home, the ambient noise is not zero. The heating or air conditioning system may be running. The compressor in the refrigerator may be running. The wind may be blowing. Cars and trucks may be passing by. Other people may be in the house moving about.

On my sound pressure level meter, the ambient noise in my house situated in the far suburbs on a dead-end street, amounts to about 35 dB. It is very quiet, but not zero.

When, for example, some claim that their favorite preamp or power amp or even DAC has a signal to noise ratio that is 115 dB and my worthless, doorstop-worthy circa-2016 item only has a signal to noise ratio of 100 dB, I must laugh. Because of the ambient noise, also referred to as the noise floor, I must get the noise above 35 dB which implies that the musical peaks will then be played back at 135 dB!!!

Please see: Loud Noise Dangers

Aside from the danger to your hearing, will your speakers and amplifier even play at 135 dB? Will the tweeters melt? Will the woofers explode into flames?

In my opinion, signal to noise ratio is only one of many factors to consider. It’s utility above, say 90 dB, is interesting but of no practical use.

 

IME, "noise floor" is used in an odd way in audio. For 30 years, I've not had a system that produced audible noise when there's no music. What are people doing that generates so much noise in their systems?

I think people use "noise floor" to mean: My system sounds better now; I perceive more detail; ergo, the noise floor must be lower. But maybe it's not noise, maybe it's IM distortion, or jitter, or bass boom that has been reduced?

I agree with @chili555 that the importance of ambient noise is often overlooked. All noise is bad, but the worst is tonal noise (i.e., noise with a pitch), such as can come from electric motors. Sometimes, an audiophile will have a $20k system, with the refrigerator humming audibly from the other room. My experience suggests, the lower you can get ambient noise, and the lower you can get distortion, the more detail you'll perceive in the recording.

 

There is inherent noise in active electronic devices like tubes and transistors, and less in resistors. In an amp or receiver with typical gain structures it is measurable and viewable on a scope, but usually not audible through high level inputs, even with the gain up full. Add a phono preamp and you might get a slight hissing sound with a sensitive speaker, although still far below the surface noise level audible while playing a vinyl record.

 

There's always noise in the audio system. It can be very, very low, especially if you're using all solid state and digital gear with all the extremely quiet op amps of the day, at average listening levels it can be below the average noise level of the listening room at the listening position (crank the system up or stick your ear next to the speaker or both and it'll be more audible). But there's always noise -- thermal noise of the active devices and resistors, ac leakage noise, induced noise from environmental sources (these two being things that don't show up in those noise specs from manufacturers), power supply noise etc. It's never zero. When you have a high gain phono pre, it can be pretty substantial. And with vinyl playback systems there's added mechanical noise from playback itself too -- from motor vibration break through and vinyl surface imperfections, and bearing rumble, etc. In my experience, lowering noise always results in more lower level detail, a greater sense of a single continuous sound space with recordings made that way, and, in the case of electrical noise, often an improvement in natural ease of presentation and reduction in a sense that the sound is hashy or grainy or hard or all those other adjectives commonly used. If the average noise level in a living room, as commonly quoted, is 40 dB, then the noise level of a digital solid state system with average efficiency speakers listened to from 10 feet, might almost always be below the ambient noise level. If you get into quiet, below grade listening rooms with a fair amount of acoustic treatment and no furnaces or anything running, you can get ambient noise levels well below that -- 15, 20 dB -- and some of this noise, or the effects of the noise at the ppp end of the dynamic scale, can be more apparent. It can also be more apparent if you're listening in the extreme near field.

 

Ah, yes, vinyl. A paradoxical subject. Audiophile nirvana, yet noisy, both mechanically and electrically. Perhaps its noise is one reason people like it?

Still, I agree on pretty much all your points. Quieter is better. (Ambient noise in my basement room is, A-weighted, somewhere in the low to mid 20s. It's too low for my Omnimic to measure accurately.) What bugs me is today's tendency to attribute every improvement in sound to "reduction of [an already inaudible] noise floor." Not pointing at you -- but one reads it frequently (without the bracketed part). It is not only "noise floor" that affects the sound!

All this while expensive tube amps are being reviewed that have > 10% THD. Yuck!

OK, rant over.

 

I may be completely wrong in my interpretation of these s/n ratios, but are they not measuring the signal from the component to the noise generated from the component itself? Not the room, surely, because no two rooms are exactly the same.

So a DAC with a s/n ratio of 115db may have a noise floor of 5db and a signal of 120db.

A quick Google search and I found that humans can begin hearing above 0db. Not sure if that is accurate. But assume it is...

- if your system's noise floor is 5db, then if your room was completely silent you may begin to hear your system at 6db or more (ignoring the fact that I believe you can hear below the noise floor, it's just more obscured)
- if your room's noise floor is 35db, it has an impact because the system can start to be heard at 6db...but not when there is 35db of noise. Music is playing at levels from 6db to 35db but your room is obscuring that.

So the higher s/n ratio components may actually be better in practice, since their higher s/n ratio is likely due to a lower noise floor. i.e. your 100db DAC may have a noise floor of 20db vs. the 5db noise floor of the DAC with a 115db ratio. I'd prefer the 115db DAC (all else equal) if my room was quiet enough. So I guess it all depends how quiet one's room is and what the system's noise floor is to figure out if it matters in practice.

Am I thinking about this correctly?

 

Not quite. Generally, a reference signal level is injected and measured. The reference is taken to be 0 dB. Then the noise level is measured and in competent modern DACs, is usually -100 dB or more.

Correct.

But to hear the noise in the DAC, the noise must exceed the 35 dB of noise in the room. That implies that the musical peaks will be 100 dB higher than 35 dB or a howitzer-like 135 dB.

For almost all of us that don't live in a subterranean anechoic chamber, a DAC with a signal to noise level that is -100 dB and therefore well below the ambient noise of the room is, on the basis of noise alone, identical to the DAC with a signal to noise level of -120 dB. That is because most of us play music at 80-90 dB or so and any noise that is in the DAC is far, far below room noise.

 

Interesting point. I'd like to raise a question about that. What if the noise at -120 dB has a different character (frequency spectrum) from the room noise? Might it not then still be audible? For example, in some rooms, most of the noise is at very low frequencies (< 100 Hz) and is due to background traffic rumble. A tonal noise at higher frequencies might still be audible, might it not? Especially if around 3kHz, where the ear is very sensitive?

Maybe someone with expertise in psychoacoustics can take this question on.

 

Got it, thanks!