16 bit, 24 bit and Noise Floor Options

[botface]

I'm involved in a discussion on a home recording forum. We are not discussing post processing, mixing or mastering just the simple capture of a single acoustic instrument.

I'm suggesting that with a recording environment that yields a noise floor of -60dbfs it makes no difference at whether you capture in 16 bit or 24 bit as you effectively only have 10 bits to work with and so any theoretical benefits of using 24 bit are lost

I'm getting arguments back like :

Specifically 24 bit capture files will still provide the widest range of dynamic and the greatest resolution for capturing anything

With 16 bit you have that many steps and with 24 you have that many more ... which means the more bits you have, the less grainy your resolution is

To give an example: You have a scale of 0 to 100. If you print it on a 10cm piece of metall you barely have enough place to distinguish 1mm distances. If you print it onto a 1m bar, you can have plenty more subdivisions. Of course 100 is still 100 and zero is still zero, but you have many more subdivisions. Same with digital signal. Say you would use a 2 db resolution: then you would have just four different levels to represent the different signal levels which would have to be somehow digitalized onto these four steps.
With 16 bit you have 2^16 possible steps (65536) and with 24 bits 2^24 possible steps (16777216, quite a bit more...). Whether you believe them to be more useful to represent an audio signal I leave to your own ears.I'm not claming that the perceived distance between noise level and maximum level is bigger with 24 bits than with 16 bits. It's just that you have many more subdivisions in between, and that is audible.

If the full theoretically possible dynamical span gets more quantizing levels per dB so must also the same dynamical span of let's say 60dB gain above recorded noise floor. I' can't see where this argument is wrong ... Maybe we're talking about different things?

16 bit recordings have a theoretical dynamic span of 96dB; 24 bit recordings one of 144 dB. If I take the number of possible representations of level with 16 bit, then I have 2^16/96 = 682,7 (rounded) steps per 1dB. WIth a 24 bit recording I have 2^24/144 = 116508,4 (again rounded) steps per 1 dB. So it seems that the dynamical resolution is much finer with 24 bit.

The scale is the same, but with 24 bits we get bigger number of smaller steps than with 16 bit at any part of the scale which allows for better resolution.
You can want to increase the dynamic range by cutting off the noise, and stretching what is left down to the negative infinity level to fill the whole range, and higher resolution of 24 bit will become very handy compared to 16 bit.

I've given examples, I've worked through the arithmetic, I've provided analogies but nobody seems to think the noise floor of the recording environment has any impact on the ability of 24 bit to capture more detail. Can any of you provide any examples or analogies that you've found to work in the past.

[icstm]

As far as I know, you can't hear tones more than about 6dB below the noise floor.

so what is the noise floor then, if i can hear below it? I am confused

A noise floor can be considered part of the signal in many situations - and be worth capturing as is.

I do not understand

A noise floor can be considered part of the signal in many situations - and be worth capturing as is.

To add another bad analogy: I always prefer MPEG2 BluRays, because they preserve film grain and noise much more conservatively than certain H.264 encoders, which add some form of softening even at very high bitrates. One could claim that this is a feature, because the latter encoder prefers allocating bandwidth to even more detailed signal than noise. But sometimes I want the noise.

I know of this preference within the cinema crowd.

I have never heard of such a thing within audio. I understand that many object to the artifacts associated with noise reduction, but preserving the crackles of vinyl or air-conditions of some recording venue does not seem to appeal to most music-lovers.

-h

Isn't that because the orginial format in Cinema includes the grainy picture. In audio, the orginal is a live or studio recording with no noise. In cinema, the orginal was NOT the live performance on stage.

A 24-bit recording has a 144 dB range. Our range of hearing intensity from quietest detectable sound to pain is 130 dB.

So 24bit recording COULD add something to the the listening experience?
(though I assume that this is theoretical, as you and I and others have said the rest of your equipment is unlikely to provide such a range or (without wanting to confuse matters) is unlikely to do so accurately)

[Arnold B. Kruege...]

A 24-bit recording has a 144 dB range. Our range of hearing intensity from quietest detectable sound to pain is 130 dB.

So 24bit recording COULD add something to the the listening experience?

Let's put it this way. The noise floor of your living room is maybe 40 dB SPL. In order to have a sound that is 144 dB above the noise floor in your living room (1OW 184 dB SPL), we'd probably have to set off some explosives and not just a little.

The loudest car stereo at national "Crank It Up" contests might be able to get that loud but trust me nobody sits inside of them during the contest. The windows have to be specially made and held in place!

Listening to sounds this loud would seriously injure you or even flat out kill you on the spot.

The flight deck of an aircraft carrier launching planes (where everybody wears full-body protective gear) is maybe 130-140 dB SPL.

Back in the real world the loudest sound in the seats at the symphony might be 110 dB when they are playing the loudest passage of the loudest musical work they play. The noise floor of the room with musicians and audience, but no music playing might be 35 dB. That gives you a dynamic range of 75 dB.

[icstm]

A 24-bit recording has a 144 dB range. Our range of hearing intensity from quietest detectable sound to pain is 130 dB.

So 24bit recording COULD add something to the the listening experience?

Let's put it this way. The noise floor of your living room is maybe 40 dB SPL. In order to have a sound that is 144 dB above the noise floor in your living room (1OW 184 dB SPL), we'd probably have to set off some explosives and not just a little.

OK, but if I look back at your other post, you are saying I can hear below the floor. So for 144dB of dynamic range I do not need 184dB SPL (i think).

[2Bdecided]

OK, but if I look back at your other post, you are saying I can hear below the floor.

You (and most people!) are confusing measurements of total signal power with measurements of the amount of signal at a given frequency.

A pure 1kHz tone (a beep) only contains one frequency, so the measure of total signal power, and the amount of signal at that one frequency, will be exactly the same for this signal.

Whereas noise can contain a spread of frequencies, with the power varying by frequency. If you have a noise signal where the power is spread evenly across all useful audible frequencies (say, 20Hz-20kHz), then for a particular total power, it'll have a lot less signal at any one frequency.

So a -100dB FS pure tone sticks up above -100dB FS noise - because at the specific frequency of the pure tone, the level of the noise is 10s of dB lower than the level of the tone.

Whether you can see/hear a tone in some noise depends on the level of the tone, the level of the noise, and how you split the signal out into difference frequency bands to try to "see"/hear details like this.

The ear has the equivalent of about 24 logarithmically spaced filters (compare this with the typical 5 filters on a classic graphic equaliser). This means you can hear a tone that measures 20-30dB lower than the total power of the noise around it - because most of that noise falls into different filter bands and can be ignored by your ears.

Cheers,
David.