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Dynamic range question, Dynamic range of hearing vs. equipment
thesurfingalien
post Jun 9 2011, 13:02
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QUOTE (MichaelW @ Jun 9 2011, 00:42) *
QUOTE (Woodinville @ Jun 9 2011, 13:02) *
Actually, the world nowadays is annoyingly noisy, when you get right down to it. (sigh)


Yes, but when I spend time in the country I'm struck by how very noisy birds can be. Not to mention the time I was having a cup of coffee on the sidewalk in urban Adelaide, and the parrots in a nearby tree were drowning the traffic noise. Real quiet is hard to find (and rather freaky when you do).


In our place in Brasil we have Cicadas (Cigarras do Brasil), and they make a terrible noise! I read that the males can produce some 100 dB, and if one starts, the rest (a lot!) follows. Listening to music, even inside, is pretty much out of the question when they go at it...

I still need to make a recording of their song and see what kind of tones they produce. That will have to wait until the winter is over. Now we have some peace and quiet here :-)
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knutinh
post Jun 10 2011, 10:31
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I seem to remember that people who record ambient sounds for movies etc (animals, weather, water) have a hard time finding spots on the earth that are not affected by passing planes, kids with a boomblaster etc. Acoustic pollution.

-k
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Kees de Visser
post Jun 10 2011, 22:18
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Absolutely ! Last year I've spent quite some time recording 3D sound ambience and it is really frustrating that most of the recording is polluted. The best option is to record hours and hours and select the usable parts (if any!) back home in the studio.
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thesurfingalien
post Jun 11 2011, 10:59
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@All,

Although all info was useful and interesting, I am still struggling with the concept of relating bit-depth to a dB scale...

Perhaps if I (again) rephrase my question...

Given that (for CD) the 16 bit depth is limiting dynamic range to 96 dB, on which basis was decided that the 96 dB was (good) enough? Why not, for example, 128 dB? To me it looks like that will only require a change in the step-size on the dB scale...

Thanks again!
Peter



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lvqcl
post Jun 11 2011, 11:11
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QUOTE (thesurfingalien @ Jun 11 2011, 13:59) *
To me it looks like that will only require a change in the step-size on the dB scale...


Sorry, but what do you mean? 'dB scale' cannot be changed by its definition.
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thesurfingalien
post Jun 11 2011, 14:11
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QUOTE (lvqcl @ Jun 11 2011, 07:11) *
QUOTE (thesurfingalien @ Jun 11 2011, 13:59) *
To me it looks like that will only require a change in the step-size on the dB scale...


Sorry, but what do you mean? 'dB scale' cannot be changed by its definition.


The scale itself can not be changed, but by step-size I mean steps of (for example) 0.1 dB or steps of 0.2 dB.

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lvqcl
post Jun 11 2011, 14:19
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QUOTE (thesurfingalien @ Jun 11 2011, 17:11) *
The scale itself can not be changed, but by step-size I mean steps of (for example) 0.1 dB or steps of 0.2 dB.


If variables A and B differ by 0.1 dB, then A/B = 1.01157945...; if A and B differ by 0.2 dB, then A/B = 1.02329299...
So... how the step-size can be changed?

This post has been edited by lvqcl: Jun 11 2011, 14:24
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thesurfingalien
post Jun 11 2011, 15:37
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QUOTE (lvqcl @ Jun 11 2011, 10:19) *
QUOTE (thesurfingalien @ Jun 11 2011, 17:11) *
The scale itself can not be changed, but by step-size I mean steps of (for example) 0.1 dB or steps of 0.2 dB.


If variables A and B differ by 0.1 dB, then A/B = 1.01157945...; if A and B differ by 0.2 dB, then A/B = 1.02329299...
So... how the step-size can be changed?


If the step-size is 0.1 dB, it takes 960 steps to get to 96 dB. For 0.2 dB that's 480 steps.
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drewfx
post Jun 11 2011, 17:33
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QUOTE (thesurfingalien @ Jun 11 2011, 04:59) *
@All,

Although all info was useful and interesting, I am still struggling with the concept of relating bit-depth to a dB scale...

Perhaps if I (again) rephrase my question...

Given that (for CD) the 16 bit depth is limiting dynamic range to 96 dB, on which basis was decided that the 96 dB was (good) enough? Why not, for example, 128 dB? To me it looks like that will only require a change in the step-size on the dB scale...

Thanks again!
Peter


96 dB of dynamic range represents the ratio of the loudest sound to the quietest sound - it's the ratio of the largest number available using 16 bits to "1". Thus to get more dynamic range, you need a bigger ratio, which means you have to add more bits.

The "step size" is fixed by the fact that it's binary.
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db1989
post Jun 11 2011, 17:37
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1 bit represents 6 dB of amplitude (i.e. a doubling/halving initially, then tailing off hence the logarithmic shape of the dB curve). Ergo 16*6=96.

This post has been edited by dv1989: Jun 11 2011, 17:38
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lvqcl
post Jun 11 2011, 18:34
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QUOTE (thesurfingalien @ Jun 11 2011, 18:37) *
If the step-size is 0.1 dB, it takes 960 steps to get to 96 dB. For 0.2 dB that's 480 steps.


1 step is 1 bit, or ~6.02 dB. 16 steps -> 96 dB.
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DonP
post Jun 11 2011, 19:21
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QUOTE (lvqcl @ Jun 11 2011, 12:34) *
QUOTE (thesurfingalien @ Jun 11 2011, 18:37) *
If the step-size is 0.1 dB, it takes 960 steps to get to 96 dB. For 0.2 dB that's 480 steps.


1 step is 1 bit, or ~6.02 dB. 16 steps -> 96 dB.


16 bits isn't 16 steps, it's 2**16 steps, a number in the range +/- 32767. In terms of "line in" voltage, each step is about 1/30 mv. If you declare that each step is twice as big, that just makes everything louder. It doesn't change the ratio between the loudest and quietest signal you can represent.
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Notat
post Jun 12 2011, 18:10
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QUOTE (thesurfingalien @ Jun 11 2011, 03:59) *
Given that (for CD) the 16 bit depth is limiting dynamic range to 96 dB, on which basis was decided that the 96 dB was (good) enough? Why not, for example, 128 dB? To me it looks like that will only require a change in the step-size on the dB scale...

During the development of the CD format, a 14-bit format (84 dB) was originally proposed. The 14-bit proposal was based on the capabilities of the ADCs and DACs available at the time and on calculations that you see in this thread of ideal dynamic range of real listening environments. The resolution was pushed to 16 bits at the insistence of Sony.
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Brand
post Jun 12 2011, 22:11
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I must admit I have the same questions as the OP regarding digital dB and "real world" dB (sound pressure) or perceived loudness.

I've been once told that going from 0 dB to -6 dB in the digital side (PC) halves the loudness. And testing this quickly seemed to confirm it.
Now, does this mean that the sound pressure dB goes from, let's say, 80 dB to 40 dB?

Also, does perhaps the relation between the digital dB and sound pressure change, depending on the volume?


QUOTE (dv1989 @ Jun 11 2011, 18:37) *
1 bit represents 6 dB of amplitude (i.e. a doubling/halving initially, then tailing off hence the logarithmic shape of the dB curve). Ergo 16*6=96.

This kind of confirms my suspicion that it's only from 0 dB to -6 dB that the halving occurs, while later a 6 dB decrease doesn't affect the loudness as much (logarithmic curve and all). But again, I'm mostly talking from some limited empirical experience/messing around. I've yet to properly grasp the theory behind this.
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DonP
post Jun 12 2011, 22:38
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QUOTE (Brand @ Jun 12 2011, 16:11) *
I must admit I have the same questions as the OP regarding digital dB and "real world" dB (sound pressure) or perceived loudness.

I've been once told that going from 0 dB to -6 dB in the digital side (PC) halves the loudness. And testing this quickly seemed to confirm it.
Now, does this mean that the sound pressure dB goes from, let's say, 80 dB to 40 dB?


Perceived loudness nominally doubles/halves with a 10 dB change, which is a 10x change in power. Perception is by nature at least somewhat subjective, so that may not be exact for you.

If your speakers are in their linear range (aka not distorting) then halving the voltage (quartering the power) is a 6 dB cut in the electrical signal and also a 6 dB cut in the acoustic power.

QUOTE
Also, does perhaps the relation between the digital dB and sound pressure change, depending on the volume?


No.

QUOTE
This kind of confirms my suspicion that it's only from 0 dB to -6 dB that the halving occurs, while later a 6 dB decrease doesn't affect the loudness as much (logarithmic curve and all). But again, I'm mostly talking from some limited empirical experience/messing around. I've yet to properly grasp the theory behind this.


No, decibels are a logarithmic scale in both domains. Again, your perception of loudness is subjective so may not perfectly track the model of 10dB = halving of apparent loudness all across the range, but a dB is the same change in measured power whether acoustic or electrical.
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lvqcl
post Jun 12 2011, 22:47
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QUOTE (Brand @ Jun 13 2011, 01:11) *
I've been once told that going from 0 dB to -6 dB in the digital side (PC) halves the loudness.

-3 dB: halves the power
-6 dB: halves the amplitude

QUOTE (Brand @ Jun 13 2011, 01:11) *
Now, does this mean that the sound pressure dB goes from, let's say, 80 dB to 40 dB?

This means that the sound pressure goes from 80 dB to 74 dB.

QUOTE (Brand @ Jun 13 2011, 01:11) *
This kind of confirms my suspicion that it's only from 0 dB to -6 dB that the halving occurs, while later a 6 dB decrease doesn't affect the loudness as much (logarithmic curve and all).

dB scale is logarithmic too.
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Brand
post Jun 13 2011, 10:25
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QUOTE (lvqcl @ Jun 12 2011, 23:47) *
QUOTE (Brand @ Jun 13 2011, 01:11) *
I've been once told that going from 0 dB to -6 dB in the digital side (PC) halves the loudness.

-3 dB: halves the power
-6 dB: halves the amplitude

QUOTE (Brand @ Jun 13 2011, 01:11) *
Now, does this mean that the sound pressure dB goes from, let's say, 80 dB to 40 dB?

This means that the sound pressure goes from 80 dB to 74 dB.

I see. I thought amplitude was directly correlated with sound pressure.
Is there another [analog] scale that's more suited for measuring amplitude changes?
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lvqcl
post Jun 13 2011, 10:51
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QUOTE (Brand @ Jun 13 2011, 13:25) *
Is there another [analog] scale that's more suited for measuring amplitude changes?

Sound pressure, measured in pascals.
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DonP
post Jun 13 2011, 12:13
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QUOTE (Brand @ Jun 13 2011, 04:25) *
QUOTE

-3 dB: halves the power
-6 dB: halves the amplitude

I see. I thought amplitude was directly correlated with sound pressure.
Is there another [analog] scale that's more suited for measuring amplitude changes?


Power is directly related to sound pressure.

The amplitude represents the voltage. Power = voltage * current, but current goes up with voltage (current = voltage/resistance)
so power is proportional to voltage squared. That's why halving the amplitude (voltage) quarters the power and makes a 6 dB difference.

I'm still seeing gaps in the basic concept of dB in this thread. When kids in middle school math class ask when they'll ever use logarithms, maybe the answer should be so they can talk about stereos. blink.gif
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Soap
post Jun 13 2011, 13:02
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QUOTE (DonP @ Jun 13 2011, 07:13) *
I'm still seeing gaps in the basic concept of dB in this thread.

I believe one of the problems seen here is a confusion concerning the difference between amplitude and power. Between the height of a wave (curve) and the area underneath said curve.


--------------------
Creature of habit.
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DVDdoug
post Jun 13 2011, 21:52
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QUOTE
Given that (for CD) the 16 bit depth is limiting dynamic range to 96 dB, on which basis was decided that the 96 dB was (good) enough?
If you listen to a file that's been reduced by 90dB, I think you'll agree it's enough...

QUOTE
Why not, for example, 128 dB? To me it looks like that will only require a change in the step-size on the dB scale...
Since all the steps are the same size (with linear PCM) and we are talking about ratios, the size of the step doesn't matter! If you run your DAC into an amplifier, the steps get bigger, and -6dB is still half. wink.gif

But, you are right! You can have a non-linear coding scheme where the steps are not equal. i.e. Imagine a logarithmic system where each step is 0.01dB. (I believe u-law and a-law encoding use a nonlinear system, but I haven't really studied these formats..)

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Northpack
post Jun 14 2011, 08:15
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I think this relation 1bit to 6.02dB is where some all-too-common misconceptions rely on. The most notorious: the digital-loathing audiophile who thinks than he can hear the "switching of the bits"... you know, those harsh digital steps in a PCM waveform who completely ruin the smooth analogue siginal. happy.gif

So, if someone really wants to explain digital audio to the layman without proper mathematical knowledge, I think it would be best to start by debunking this very misconception, explaining why there isn't such a thing as an arbitrary step size in digital audio and how the dynamic range is limited by quantization noise.

Anyone interested in writing such an explanation? I think it could save hundreds of souls from ignorance... he or she would gain some Karma!

This post has been edited by Northpack: Jun 14 2011, 08:21
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knutinh
post Jun 14 2011, 09:13
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QUOTE (Northpack @ Jun 14 2011, 09:15) *
I think this relation 1bit to 6.02dB is where some all-too-common misconceptions rely on. The most notorious: the digital-loathing audiophile who thinks than he can hear the "switching of the bits"... you know, those harsh digital steps in a PCM waveform who completely ruin the smooth analogue siginal. happy.gif

So, if someone really wants to explain digital audio to the layman without proper mathematical knowledge, I think it would be best to start by debunking this very misconception, explaining why there isn't such a thing as an arbitrary step size in digital audio and how the dynamic range is limited by quantization noise.

Anyone interested in writing such an explanation? I think it could save hundreds of souls from ignorance... he or she would gain some Karma!

Properly dithered digital behaves similar to analog systems where the noise floor is (best case) about 6*#bits below the maximum signal.

For CD (16 bits) this works out to be about 96dB, or 2^16 or 65536:1. For hirez formats using 24 bits, this would ideally mean 144 dB, but in practice man cannot make AD and DA-converters of such high precision.

When doing proper level-aligned blind testing, somewhere around 14-16 bits seems to*) be enough for all sound playback applications. More resolution mainly buys you peace of mind.

-k
*)Blind tests cannot prove that any resolution is "high enough" for all applications, but it repeatedly failing to prove it is often considered a convicing indication.

This post has been edited by knutinh: Jun 14 2011, 09:14
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Fedot L
post Jun 14 2011, 10:43
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QUOTE (Brand @ Jun 13 2011, 09:25) *
...I thought amplitude was directly correlated with sound pressure.

Yes, it is.
===
QUOTE (lvqcl @ Jun 13 2011, 09:51) *
Sound pressure, measured in pascals.

Sure.
===
QUOTE (DonP @ Jun 13 2011, 11:13) *
Power is directly related to sound pressure.

Electric power of an amp is directly related to sound intensity (acoustic intensity), W/m2 (watts per square metre), and sound pressure is directly related to voltage.
http://en.wikipedia.org/wiki/Sound_intensity
===
QUOTE (DonP @ Jun 13 2011, 11:13) *
I'm still seeing gaps in the basic concept of dB in this thread.

QUOTE (Brand @ Jun 13 2011, 09:25) *
Is there another [analog] scale that's more suited for measuring amplitude changes?

I hope, two conversion instruments links may help in particular cases:

1. dB vs V (or Pa).
Substitute V for voltage or Pa (pascal) for "sound pressure":
http://www.crownaudio.com/apps_htm/designtools/db-volts.htm

2. dB vs W (or W/m2).
Substitute W for wattage or W/m2 for "sound intensity":
http://www.fab-corp.com/pages.php?pageid=1

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Northpack
post Jun 14 2011, 11:00
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QUOTE (knutinh @ Jun 14 2011, 09:13) *
Properly dithered digital behaves similar to analog systems where the noise floor is (best case) about 6*#bits below the maximum signal.

Sure, that's the way it is, you and I know that because we know the math behind digital audio. But it is not an explanation to those who don't know the math and are misguided by audiofoolish reasoning. If you want to enlighten people you have to explain things in a way they can follow instead of making assertions, how true they may be. That's why Plato always wrote in the form of dialogues...

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