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Is -140 the limit in measurements?

Wombat

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Probably, but your amps, and mine, are very quiet, so I was interested in what it sounds like, if anything. I don't consider it relevant to normal playback but I'm interested in how the ear + brain might might compare to the analyser + FFT.

The ear won't hear or process it.
 

Speedskater

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Readings well below -140dB can be made but it's not easy. First build a double shielded room, light the room with old fashioned incandescent light bulbs powered by DC, nothing electrical in the room but the test stuff. Then make hundreds of measurements and average the results. With that method the noise drops way down. Amateur astronomers have been doing it that way with budget telescope cameras.
 
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S

stalepie

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Turning it up is cheating. isn't it? If I turn up the volume high in a frequency sweep I can hear past my limits into 17kHz+
 

RayDunzl

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JohnPM

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Not difficult to go below -140 dBFS, but not many analog signal chains that have much to see there. More useful for digital data paths. See some examples here.
 

DonH56

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Note the noise floor on an FFT is not the same thing as the SNR... SNR integrates the noise over the entire measurement bandwidth, while the noise floor is the range from peak signal to smallest signal in a 1 Hz (or one FFT bin) bandwidth. And amp with a 120 dB SNR will necessarily have a lower noise floor measured by an FFT. Think of adding (actually root-sum-squaring) all those tiny little spikes at the noise floor; the answer compared to the signal tone is the SNR.

Another example: for a data converter (ADC or DAC) the SNR is roughly 6N+2 dB where N is the number of bits; the noise floor (spurious-free dynamic range, SFDR) is ~9N dB. A 16-bit DAC has an SNR of ~98 dB from quantization noise alone but the SFDR ("noise floor") is ~144 dB (there's that number again) assuming no other distortion (or clock spurs, etc.)

HTH - Don
 

Soniclife

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I tried it, -120db is as low as audacity will go, if my maths is correct.
I tried -96 first, at 00.0 on my volume control* I can hear a quiet tone near the speakers at the listening position, if I turn the volume down to -15.0 I can no longer hear it at the listening position.
-120db, not audible at the listening position at 0.00, if I turn the volume up to +13.5 I start to hear it at the listening position. It is audible at 0.00 with my ear very close to the speaker.
When listening I occasionally get as high as -4 with quiet digital recordings being played loud, most of the time maximum is around -15 when I have turned it up, volume peaked at -13.5 last night. Current noise floor in my room is attached, I'm always surprised it goes below 0db for part of the range.

* The amp is a Devialet, below zero on the volume is done by digital attenuation, above zero is digital gain, so a form of cheating for this test. It's completely noise free at all volume settings.
 

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Arnold Krueger

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The proposed experiment, which appears to be to simply try to create a low-level signal and try to hear it, lacks refinements for which I will try to make a logical care for.

The first thing is that in all reasonable likelihood you really don't want to try to listen for the lowest level recording that you can hear.

Rather you want to listen for the lowest level sound that you can hear played in an audio system with its gain set at a reasonable, comfortable and real-world level for the recording at hand. So it might be more likely that you want to listen to a recording of a sound presented at a reference level that is comfortable for you and then you want to listen to the low-level test sound(s).

Your goal is to set the reference sound for a reasonable, comfortable and real-world SPL such as the one you would set your system for were you going to do some engaged listening.

One way to accomplish this is to listen to the reference sound and adjust it until it sounds right to you, given that your goal is engaged comfortable listening.

Secondly, you don't want to go straight from listening at a reference level straight to the lowest level, because that is typically not what happens in real-world listening. In most music and dialog the periods of high loudness and low loudness are separated by transitional periods.

Thirdly you don't want to plunge the listener cold turkey into the most critical listening situation. Again, it is easier for people to do well in listening tests if they transition from easy even non-challenging listening to challenging listening in a gentle progression.

Fourthly, you don't want to create a crisis where the listener has to do or die. Instead, you want to create a situation where less-than-perfect performance is rewarded a little while preserving a good reward for better performance.

Finally, you want an experiment that is open-ended, because we are dealing with people, and people always have the potential to surprise y0u with how well or how badly they perform. We want answers from the real world, not answers of our choice or based on our foregone conclusions.

With all those things in mind. I humbly present for your entertainment an ergonomically designed listening test, encapsulated in a file that you can download from here: https://www.dropbox.com/s/n50g7b6hs14x8dj/high resolution listening test audacity HD.flac?dl=0

The instructions are for you to adjust the first two repetitions of the recorded vocal sound for comfortable, engaged listening, and report back the number of times you can hear the sound repeated, including the first two repetitions.

Please note that the actual detailed characteristics of the sound are less important since the goal of the evaluation is to hear how much the same identical sound can be attenuated and still be heard. If it were in the realm of the peak sensitivity of the ear, then it would be set lower during the initial reference level setting, If the sound was in some realm where the sensitivity of the ear was less, then following the instructions would result in it being set up with more gain and actual SPL level
 
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Arnold Krueger

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I tried it, -120db is as low as audacity will go, if my maths is correct.
I tried -96 first, at 00.0 on my volume control* I can hear a quiet tone near the speakers at the listening position, if I turn the volume down to -15.0 I can no longer hear it at the listening position.
-120db, not audible at the listening position at 0.00, if I turn the volume up to +13.5 I start to hear it at the listening position. It is audible at 0.00 with my ear very close to the speaker.
When listening I occasionally get as high as -4 with quiet digital recordings being played loud, most of the time maximum is around -15 when I have turned it up, volume peaked at -13.5 last night. Current noise floor in my room is attached, I'm always surprised it goes below 0db for part of the range.

* The amp is a Devialet, below zero on the volume is done by digital attenuation, above zero is digital gain, so a form of cheating for this test. It's completely noise free at all volume settings.


Friendly advice - it is fair to attenuate a signal repetitively with whatever attenuation is at hand in order to achieve the desired level of attenuation.

However, beware I have found that some audio editing software , if used to repeatedly attenuate a passage a large number of times, may subtly adversely affect the frequency response of the signal. Therefore, a reasonable way to greatly attenuate a signal if steps is to attenuate it repetitively in a few steps, and then copy and paste the attenuated steps and attenuate that new group with a larger amount of attenuation, in order to create a longer sequence of steps that are widely-ranging.
 
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Arnold Krueger

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Note the noise floor on an FFT is not the same thing as the SNR... SNR integrates the noise over the entire measurement bandwidth, while the noise floor is the range from peak signal to smallest signal in a 1 Hz (or one FFT bin) bandwidth. And amp with a 120 dB SNR will necessarily have a lower noise floor measured by an FFT. Think of adding (actually root-sum-squaring) all those tiny little spikes at the noise floor; the answer compared to the signal tone is the SNR.

Another example: for a data converter (ADC or DAC) the SNR is roughly 6N+2 dB where N is the number of bits; the noise floor (spurious-free dynamic range, SFDR) is ~9N dB. A 16-bit DAC has an SNR of ~98 dB from quantization noise alone but the SFDR ("noise floor") is ~144 dB (there's that number again) assuming no other distortion (or clock spurs, etc.)

HTH - Don

An overview of the test environment is that due to the statistical nature of random or pseudo-random noise, noise measurements are only proper and reasonable if made in a known or defined bandwidth.

One common reference bandwidth is 20-20 KHz flat mid-band and -3 dB at the stated limits, with 6 or 12 dB roll-offs beyond that.

Another common measurement band is "A weighting" which is to be a simplistic analog filter approximation of the sensitivity of the ear at a relatively low SPL of -40 dB SPL

600px-Lindos4.svg.png


https://en.wikipedia.org/wiki/A-weighting

https://www.johndcook.com/phon_sone.html

600px-Acoustic_weighting_curves_%281%29.svg.png
 
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trl

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I made a -90dB file, and it plays very softly with the preamp full on (an unbearable level with normal source).

I don't think there would be anything to hear another 50dB down here.

I was using https://xiph.org/~xiphmont/demo/1kHz-105-dither.wav for several times to compare background noise of amplifiers and DAC dynamic. I am using very sensitive headphones and on the playlist of Foobar/jRiver there's only this file and no other! If a 0dB file plays when volume to the max. then hearing might get lost instantly!
 

Speedskater

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However, beware I have found that some audio editing software , if used to repeatedly attenuate a passage a large number of times, may subtly adversely affect the frequency response of the signal.
That probably works the same way as editing 'jpeg' photos. You never want to edit a jpeg, save it then reopen it for further editing.
 

Arnold Krueger

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That probably works the same way as editing 'jpeg' photos. You never want to edit a jpeg, save it then reopen it for further editing.

As long as you restrict yourself to editing only losslessly-encoded files like .wav or FLAC, it is not nearly the same thing as editing lossy-encoded JPEGs.

You can close and reopen editing with reasonable impunity.

In the specific case where I saw spurious losses, the number of opens and closes was like a dozen, and the losses were still only a fraction of a dB. But, I'm used to much better accuracy than that!
 

restorer-john

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We can indeed make the electrons shut up. Just reduce the temperature to absolute zero.

* Imagining Amir shivering inside a huge freezer with his AP, digging deep into that noise floor...
 

trl

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[...]
When listening I occasionally get as high as -4 with quiet digital recordings being played loud, most of the time maximum is around -15 when I have turned it up, volume peaked at -13.5 last night. Current noise floor in my room is attached, I'm always surprised it goes below 0db for part of the range.
[...]
Not sure I understand your graph, sorry. I was expecting something relative to human hearing, as it could be more representative for me. AFAIK below +10dB our hearing is not sensitive anymore.

Experiment: I had a friend that got to a phonic isolated (anechoic) room at Technical University from IASI, RO (prisms with rock-wall on walls, ceiling and floor); his teacher did a bet with him: "I'll pass you to my exam if you can sit inside this isolated room for 1 hour". After about 10 minutes my friend said STOP and got out of the room. He told me that he was extremely anxious and it was impossible to stay there any longer; he said something about an inside noise between 0dB and +10dB (hope I do remember well). Funny thing, his noises he made were also absorbed by the room, so probably this was causing his anxiety and nervosity more than the background noise itself. It's called "deaf room" and you will be able to hear your heart beating and your blood through your veins; here's an article about it (again, Google Translate is our friend):
- https://www.bzi.ro/secventa-incendi...ste-face-toti-banii-galerie-foto-video-503706

In my bedroom at night I estimate an average noise of +20dB across audible range.However, I'll have it measure this weekend with REW.
 

Soniclife

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Not sure I understand your graph, sorry. I was expecting something relative to human hearing, as it could be more representative for me. AFAIK below +10dB our hearing is not sensitive anymore.
It's the noise floor in my lounge when it's quiet outside, it's measured with a umk1 and the rta in rew, it shows there is little background noise to mask sounds in my room. 0db is the limit of how quiet humans can hear.

My room is quiet, but reflective, so sound bounces around a bit too much, not at all like an anechoic chamber.
 
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