Audio loudness vs Audition's db meter

[raptor888]

What is the perceived loudness difference between two sounds on Audition's timeline, verses the db indicator at the bottom of the Audition display?

For instance, I made a generator quiet box and recorded a video of the generator running alone and then with the generator enclosed in the quiet box.  I imported the audio into Audition.  When I compare the loudness of the before and after, the generator running alone shows -9 db and when enclosed in the quiet box it shows -30 db.  There is quite a difference listening to the audio but I want to know numerically how much quieter the "after" sound is compared to the "before" sound via the db meter.

To me the "after" loudness sounds about 15% of the "before" loudness.  Is there a standard that says how much the sound decreased between -9 db and -30 db numerically?  Like maybe a percentage or 8x quieter or whatever.

[ryclark · Accepted solution]

The difference is 21dB which in 'loudness' terms is about a factor of 4 less. However the human ear isn't equally sensitive across all frequencies and also the 'quiet' box won't be able to reduce the low frequencies as much as the mid and high ones due to the laws of physics. So what you hear may not be the same as you are actually measuring as peaks across a broadband metering system such as Audition's level meters.

Really to measure accurately you need to use a proper SPL (sound pressure level) meter with 'A' weighting. However all you can go by with your experiment is that the 'quiet box' makes both an audible and level reduction. You will get a bit more idea of how the 'quiet box' is performing if you look at the Frequency Analysis window in Audition which will show the effect across the audio frequency band..

[SteveG_AudioMasters_]

ryclark  wrote

The difference is 21dB which in 'loudness' terms is about a factor of 4 less.

Actually in SPL terms it's 11.2x, but like I said, it's meaningless.

[SteveG_AudioMasters_]

The reason that dB are used is that this is the sensible way of enumerating it! dB are logarithmic, and they are a much closer correlation with the way your ears work than percentages are. So, if you have reduced the noise (and you've kept everything the same about the recording) by 21dB, you already have a more meaningful figure of sorts. What you won't have though is a response curve for how much reduction you've achieved - the chances are that you will have attenuated the high frequency noise a lot more effectively than the low frequency noise, which is much harder to mitigate. And that alone will also make a bit of a mockery of any percentage figure, I'm afraid.

On top of that, in order to make a truly meaningful measurement, you need to use a calibrated mic, if you are going to establish how this sits in terms of other measurements people have made. If you only want it as a local comparison, then it doesn't matter so much. If you really want to do the job properly though, you need to hire a Sound Intensity meter and do a proper before/after noise plot, although they can be a bit of a nightmare. These measurements are the basis of those numbers you see on the side of a lot of power tools. There are loads of places that you can get information about this - typically Sound Intensity Testing and Analysis: Siemens PLM Software - but you'll find that all of them use dB!

[raptor888]

ryclark and SteveG,

Thanks both for your informed feedback.  So in loudness terms it's a factor of 4 less (or 25%), and in SPL terms it's 11.2x less.  A bit confusing for a layman like me.

I guess that all I can do without a SPL meter or other measuring equipment, is to listen to the audio playback and to "estimate" that the quiet box sound level is about 20% of the naked generator's sound level.  It's a "in my estimation" thing which will vary for different people.

Thanks for your help,

Raptor88

[SteveG_AudioMasters_]

raptor888  wrote

It's a "in my estimation" thing which will vary for different people.

That's why we go for qualified measurements. People's perception of them may vary, but it's a lot harder to argue with calibrated measurements taken in an ISO-approved manner, when it comes to the crunch. And yes, there are some noise sources that are a lot more controversial than others - aircraft noise is a particular one, and any noise with a very low frequency content appears to be perceived significantly differently by many people. The whole thing is a complete minefield when you look into it in any depth!

[Bob_Howes]

My friends who responded earlier will probably laugh at me, but...

You may wish to consider downloading an app called "RTA" for your phone.  The base version is free and the so called pro one is five of six dollars.  As you might guess from the price and the fact it uses phone mics, it's not a professional audio tool but, for basic measurements, it's surprisingly accurate and lets you measure SPL (sound pressure level) in A. B or C format and also gives you a readout of what frequencies are at what level.  I use mine mainly when I do live work to do a rough check of levels and frequency response in various parts of the auditorium.

[SteveG_AudioMasters_]

https://forums.adobe.com/people/Bob+Howes  wrote

for basic measurements, it's surprisingly accurate and lets you measure SPL (sound pressure level) in A. B or C format and also gives you a readout of what frequencies are at what level.

You've, er, checked that against a standard calibrator, have you?

[ryclark]

I am OK with dBs when it comes to voltage ratios but still tend to get confused when it comes to power, loudness and SPL. I knew that 21dB was just over 10x voltage wise but wasn't sure how that translated to perceived loudness.

Perhaps Bob meant that it seems surprisingly accurate or at least accurate enough.

[SteveG_AudioMasters_]

ryclark  wrote

I am OK with dBs when it comes to voltage ratios but still tend to get confused when it comes to power, loudness and SPL. I knew that 21dB was just over 10x voltage wise but wasn't sure how that translated to perceived loudness.

That's the problem in this case - it simply doesn't relate at all! If you change the frequency profile of the sound (which is inevitable if there's any broad spectrum noise, and you've attenuated it), then a simple pressure reading - on its own - won't tell you anything. Specifically, anybody who is more sensitive to LF noise is going to tell you that the reduction is far less than somebody who's only interested in the HF, which it is much easier to reduce the transmission of.

As far as power and SPL are concerned, the relationship is essentially the same as between Watts and Volts - there's a square law relationship. One's experience of loudness is the same as sticking your fingers in a power socket; if they're wet it's going to hurt a lot more... sound intensity though is Watts/m^2 and you wouldn't express it in dB either. If you really want to measure loudness, you use phons...

There's a reasonably good explanation here: https://community.plm.automation.siemens.com/t5/Testing-Knowledge-Base/Sound-Pressure-Sound-Power-an...  although they use temperature and a fire to explain the difference. That analogy isn't very accurate though, if you think about it...

[Bob_Howes]

SteveG(AudioMasters)  wrote

https://forums.adobe.com/people/Bob+Howes   wrote

for basic measurements, it's surprisingly accurate and lets you measure SPL (sound pressure level) in A. B or C format and also gives you a readout of what frequencies are at what level.

You've, er, checked that against a standard calibrator, have you?

As a matter of fact, yes--sort of.  From my pre retirement days I still have my "real" RTA and Earthworks measurement mics--but I have to admit they haven't had their annual calibration check for a few years!

[ryclark]

If they are anything like us oldies then their HF response has probably dropped off over the years.

[Bob_Howes]

Sigh.  Yeah, my HF was down to about 14K last time I checked.

However, more worrying is the ear bud generation.  For fun one night, we did a rough frequency response on my grown son and his friends and (at least at that point--me mid 50s  and them early 20s) their HF response was worse than mine.

[SteveG_AudioMasters_]

Yes, the 'earbud' generation are going to be pretty much shafted from that POV. What they don't seem to realise is that if you keep those things in your ears running at anything over 85dB for any length of time, ear damage is inevitable. And judging from what I've heard emanating from the outside of some of them, it's quite normal to run them at significantly higher levels than that. If you do this on a daily basis, eventually (and possibly sooner than you think) you're going to have to use them as a hearing aid...

I'm quite fortunate - I can't use them, as nothing short of specially crafted ones will stay in my ears, and anyway, I find them to be rather uncomfortable.

Presbycusis is inevitable to a degree - natural ageing plays a part, but on its own, it does nothing like the damage that even normal urban living does, and earbuds are way worse than that.

[raptor888]

https://forums.adobe.com/people/Bob+Howes  wrote

You may wish to consider downloading an app called "RTA" for your phone.  The base version is free and the so called pro one is five of six dollars.  As you might guess from the price and the fact it uses phone mics, it's not a professional audio tool but, for basic measurements, it's surprisingly accurate and lets you measure SPL (sound pressure level) in A. B or C format and also gives you a readout of what frequencies are at what level.  I use mine mainly when I do live work to do a rough check of levels and frequency response in various parts of the auditorium.

Thanks for this tip.  I'll give RTA a try the next time I want to measure audio loudness.