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TorQueMoD2
Inspiring
July 15, 2023
해결됨

how to know the real-world db level of a file?

  • July 15, 2023
  • 1 답변
  • 2205 조회

So, I understand that the negative db value shown in Audition is based on a reference point and that 0 is the loudest volume before distortion will occur, and basically, anything below -27 is inaudible (-96 is silence). How does one know the actual db level of an audio file? Obviously, it depends on the volume level of the output, but assuming your speaker level is 100% is it possible to infer a positive db? I'm guessing not because it would vary from speaker to speaker.

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최고의 답변: SteveG_AudioMasters_

I don't think it's the math you are having a problem with - it's the concepts behind this. I will try and explain it as simply as I can without using too many numbers...

 

The most important point is that dBs aren't absolute units - you can set the reference point anywhere you like - as long as you've indicated where your reference value is. Pascals ( a microPascal is one millionth of a Pascal) are an absolute unit of pressure, so you can use these to indicate where you are setting your relative pressure reference value at. So for convenience with acoustic measurements, we can set our 0dB value to be at 20 micropascals, and that level is about where the threashold of hearing is - so everything louder than that has a positive number. And that's where things like the lawnmower get their values from. So strictly speaking, that should read 95dB ref 20 microPascals.

 

Audition of course has it the other way around - the reference you are worried about there is the point at which it overloads, and by custom and practice this has always been referred to as 0dB. So quieter sounds all have lower values than this. But the important thing is that this isn't an absolute pressure value - so doesn't relate directly to the real world of things making a noise at all. Which means of course that you cannot use Audition for these sorts of measurements - well, not directly anyway.

 

To measure real-world levels you have to use a Sound Pressure Level meter, and to be accurate, they have to be calibrated. This happens using a device producing a fixed-level tone at a known level. When you've calibrated your meter, then you can determine the levels of sounds using it. This is NOT simple and straightforward - I'm only giving you a brief overview of the situation; in practice there is a heck of a lot you have to understand and take account of before you can get a reliable value.

 

To a first approximation, using the 20 microPascal level as 0dB, then the threshold of hearing is at 0dB, and the threshold of pain is at about 120dB. When you are exposed for any length of time to sounds above about 85dB, you are likely to suffer from at least temporary hearing threshold shift - which is why it's set as the lowest 'action' level - for continuous exposure above it, you are advised to wear hearing protection. You are okay with the lawnmower for two reasons; firstly you aren't really exposed to it for that long as a rule, and secondly, the point at which 95dB is reached is at a fixed distance from the source of the noise, and you are actually further away than that - so it's not that loud at the place your ears are.

1 답변

SteveG_AudioMasters_
Community Expert
SteveG_AudioMasters_Community Expert
Community Expert
July 15, 2023

'Anything below -27 is inaudible'? You must be joking! You can hear sound levels a long way below that, and -96dB isn't 'silence' either. Rather than have me explain it all here, perhaps you'd like to look at this which will explain it for you, and tell you what the reference values are.

T
TorQueMoD2작성자
Inspiring
July 16, 2023

Oh, that's what I read through my searches (-96 being silence). Apparently that wasn't correct. I said the -27 was inadable based on it looking like the lowest value in Audition so that part just came from my own assumptions. I only use the software casually so my understanding is clearly lacking 🙂
But is there a way to get an estimate of a positive db level? Like I read that a lawnmower is somewhere around 95db so it's hard for me to figure out how loud my audio file is when I see everything in a negative range. The link you provided is just too technical for me to make sense of (I could follow along until they mentioned micro pascals). Especially since in that article, they say that the reference value is equated to Zero, and yet it's supposed to be the quietest sound a human can hear, and yet everything else I read says that 0 is the loudest sound before distortion in Audition. It's kind of like I have a 4-year-old's grasp of math and you just asked me to read a university paper on calculus 😛 I understand the words, but it didn't really clarify much for me.

SteveG_AudioMasters_
Community Expert
SteveG_AudioMasters_Community Expert답변
Community Expert
July 16, 2023

I don't think it's the math you are having a problem with - it's the concepts behind this. I will try and explain it as simply as I can without using too many numbers...

 

The most important point is that dBs aren't absolute units - you can set the reference point anywhere you like - as long as you've indicated where your reference value is. Pascals ( a microPascal is one millionth of a Pascal) are an absolute unit of pressure, so you can use these to indicate where you are setting your relative pressure reference value at. So for convenience with acoustic measurements, we can set our 0dB value to be at 20 micropascals, and that level is about where the threashold of hearing is - so everything louder than that has a positive number. And that's where things like the lawnmower get their values from. So strictly speaking, that should read 95dB ref 20 microPascals.

 

Audition of course has it the other way around - the reference you are worried about there is the point at which it overloads, and by custom and practice this has always been referred to as 0dB. So quieter sounds all have lower values than this. But the important thing is that this isn't an absolute pressure value - so doesn't relate directly to the real world of things making a noise at all. Which means of course that you cannot use Audition for these sorts of measurements - well, not directly anyway.

 

To measure real-world levels you have to use a Sound Pressure Level meter, and to be accurate, they have to be calibrated. This happens using a device producing a fixed-level tone at a known level. When you've calibrated your meter, then you can determine the levels of sounds using it. This is NOT simple and straightforward - I'm only giving you a brief overview of the situation; in practice there is a heck of a lot you have to understand and take account of before you can get a reliable value.

 

To a first approximation, using the 20 microPascal level as 0dB, then the threshold of hearing is at 0dB, and the threshold of pain is at about 120dB. When you are exposed for any length of time to sounds above about 85dB, you are likely to suffer from at least temporary hearing threshold shift - which is why it's set as the lowest 'action' level - for continuous exposure above it, you are advised to wear hearing protection. You are okay with the lawnmower for two reasons; firstly you aren't really exposed to it for that long as a rule, and secondly, the point at which 95dB is reached is at a fixed distance from the source of the noise, and you are actually further away than that - so it's not that loud at the place your ears are.

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