Noise Floor

[Nikhil]

Ambio,

Just want to point that out the difference between the terms "Noise Floor" and "Noise". Noise Floor is a noise level (usually the average noise level) that is unique to any particular system. Others on here have given lots of info on what is noise and what it can comprise of.

The graph I have given shows "Noise" whereas the "Noise Floor" would appear as a flat horizontal line parallel to the horizontal time axis and would represent the average or max noise (depending on what you want to see). The "height" or level of this line from the horizontal axis would then be called the "Nose Floor". Noise can change during the song due to all the different factors that make up noise.

Your assumption that this noise is so low that it is trivial is not correct. Noise ultimately smears the original signal - usually in the time domain. It is always beneficial to reduce noise so that you get to hear the best signal. In that sense the graph I have given is as close to the truth as can be approximated.

 

[Ambio]

For a given pro-driver for HF with 110dB sensitivity, if we take 1W @ 8ohms @ 2.83V then 150uV becomes 25dB, which is way above threshold of hearing and easily recognizable if you sitting straight in front of the HF unit.



No where i have said it is very loud hiss, but if you are sitting in a normal silent listening room and enjoying a low level music, you can easily make out the hiss as an annoying factor with 110dB speakers during quite passages.

Thank you very much for the quick response. As per your calculation, the noise level is 25dB for this crown amplifier while outputting 2.83V. Now, let's go back to the formula you gave in the earlier post on how to derive SNR.

Using these figure, the SNR is 85 dB only. That is far too low then the crown amplifier of 100dB SNR. If I were to use the Crown amplifer I would only hear about 7 dB of noise floor . In reality, I am not going to listen at 110dB. nor would I hear them in my 40 dB noisy room.

Please check my calculation. I am bit rusty.

 

[Ambio]

Ambio,

Just want to point that out the difference between the terms "Noise Floor" and "Noise". Noise Floor is a noise level (usually the average noise level) that is unique to any particular system. Others on here have given lots of info on what is noise and what it can comprise of.

The graph I have given shows "Noise" whereas the "Noise Floor" would appear as a flat horizontal line parallel to the horizontal time axis and would represent the average or max noise (depending on what you want to see). The "height" or level of this line from the horizontal axis would then be called the "Nose Floor". Noise can change during the song due to all the different factors that make up noise.

Your assumption that this noise is so low that it is trivial is not correct. Noise ultimately smears the original signal - usually in the time domain. It is always beneficial to reduce noise so that you get to hear the best signal. In that sense the graph I have given is as close to the truth as can be approximated.

Hi Nikhil,

I am grateful or those graphs. If somehow we can relate the NF and get to the point then hearing the lower NF with change of equipment is possible. I am still trying to understand them in relation to how much of NF we are talking for an effective audible change and if such change can be accurately represented as shown in the graphs.

I apologise if I sounded dismissive of your contribution. it just my way of expressing myself.

Thanks.

 

[prem]

Ambio, i am curious. What is the objective of this exercise apart from possibly learning some new technical jargon?

 

[Ambio]

Ambio, i am curious. What is the objective of this exercise apart from possibly learning some new technical jargon?

Objective- to know the actual noise floor that you can hear in normal music level. If you can't hear the noise floor then any further reduction shouldnt be audible. Having said that, it may be possible that thousands of audiophiles are hearing them regularly and I am trying to find out whether it is the NF or something else.

 

[dheerajin]

For those, who are just getting bouncers....in simple terms...chemical formula for ethyl alcohol is c2h5oh and it is same in cheap liquor or expensive...so cheaper(desi) liquor has more noise content and expensive(scotch&single malt) has lesser noise...so expensive gear is designed to have less noise floor..[emoji6] ..hope this explains

 

[Ambio]

Please see How Much Distortion Can We Hear With Music? An Axiom Experimental Study. It is remarkable for a manufacturer to put the money where the mouth is.

The highlights of the findings..

Total Harmonic Distortion plus Noise (0.03% THD + N)seem fairly abstract on the page. We can scan the percentages or look at the graphs of relative distortion versus an amplifier or loudspeaker's output at various listening levels, but it's hard to imagine what those figures represent under real-world listening conditions. Will we hear it with music? How much distortion can we tolerate or even detect?

it's worthwhile viewing distortion numbers with caution when making a purchasing decision. Ever-lower distortion numbers may not contribute to improved sound quality.

Bryston and Yamaha Pro amplifiers were used in the playback chain.

Interestingly, the results demonstrated that the average amplitude level of the music playback did not affect the noise detection results. At each test level, the ability of listeners to detect the noise distortion depended on the relative loudness of the noise signal to the music, not on the overall average loudness of the music.

The congruity is remarkable. Only one obvious deviation at 10 kHz, for the oldest listener in the tests, shows any significant departure away from the other listeners' curves. Even at much higher frequencies, 5 kHz for example, the distortion tone had to be raised to an average of just 30 dB below the music level (about 3% distortion) before listeners could hear it along with the music.

The Results

While it is has been recognized for years that human hearing is not very sensitive to low bass frequencies, which must be reproduced with much more power and intensity in order to be heard, what these results show is that our detection threshold for noise (made up of harmonically related and non-harmonically related test tones) is practically non-existent at low frequencies. (The noise test tones are noise in the sense that they are not musically related to tones commonly found in musical instruments.) In fact, the noise tones at 20 Hz and 40 Hz had to be increased to levels louder than the music itself before we even noticed them. Put another way, our ability to hear the test frequency noise tones at frequencies of 40 Hz and below is extremely crude. Indeed, the results show we are virtually deaf to these distortions at those frequencies. Even in the mid-bass at 280 Hz and lower, the noise can be around -14 dB (20% distortion), about half as loud as the music itself, before we hear it.

Conclusion

Axiom's tests of a wide range of male and female listeners of various ages with normal hearing showed that low-frequency distortion from a subwoofer or wide-range speaker with music signals is undetectable until it reaches gross levels approaching or exceeding the music playback levels. Only in the midrange does our hearing threshold for distortion detection become more acute. For detecting distortion at levels of less than 10%, the test frequencies had to be greater than 500 Hz. At 40 Hz, listeners accepted 100% distortion before they complained. The noise test tones had to reach 8,000 Hz and above before 1% distortion became audible, such is the masking effect of music. Anecdotal reports of listeners' ability to hear low frequency distortion with music programming are unsupported by the Axiom tests, at least until the distortion meets or exceeds the actual music playback level. These results indicate that the where of distortionat what frequency it occursis at least as important as the how much or overall level of distortion. For the designer, this presents an interesting paradox to beware of: Audible distortion may increase if distortion is lowered at the price of raising its occurrence frequency.

 

[Thad E Ginathom]

What is Dynamic Range?

A video of a lecture by "JJ" Johnston.

I'm a great fan of JJ, because he tells it as it is, with the experience of decades of having probably been as deep into digital (and analogue) audio as anybody can get, and being able to explain in such a way that even maths dunces like me can begin to understand.

But watching this video properly is still on my to-do list. I'm sure we'll find it worthwhile

 

[Ambio]

Just found out the SNR of most reference microphones are just in the 70s dB range. The noise floor itself in the 20s dB! Wonder what good buying amplifiers or preamplifiers with SNR over 100dB?