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O2 AMP + ODAC - Page 152

post #2266 of 5263
Hi, thanks for your input. So 24bit goes lower & higher in the frequency range than 16bit? I did not know that. I just assumed it referred to the amount of detail contained within the file and not the range.

I'm always learning.
post #2267 of 5263
Quote:
Originally Posted by jring View Post
 

 

Hi,

 

reducing output level in software makes a difference when you're running a DAC in 16 bit mode because the dynamic range the human ear can measure is about 16 bit.

 

That's the reason why running a DAC in 24 bit mode is useful (unlike higher sample rates imho) - you can use software volume with impunity - regardless of the question whether your material is 24 bit or 16 bit upscaled.

 

Joachim

 

Interesting. No offense, but I do not think it works this way. Something tells me this oversimplification has lead to a fallacy.  The volume level is mapped to more bits. But when turned to half volume, you are still dealing with half of the available information.  All the extra bits give you is a more graduated scale between no volume and full volume. This does not mean you just can throw away the bits to no effect, which is what you are implying.  

 

So there must be something I am not understanding of your explanation. Are you talking about 16-bits being mapped to the lowest order of 24-bits? Is that what is actually happening? This would mean the last part of the range of volume would make no audible difference at all. I do not think this is the case.

 

Like I said, I may be misunderstanding something here. :normal_smile :

 

BG


Edited by r010159 - 3/27/14 at 3:10am
post #2268 of 5263
Quote:
Originally Posted by Zorrofox View Post

Hi, thanks for your input. So 24bit goes lower & higher in the frequency range than 16bit? I did not know that. I just assumed it referred to the amount of detail contained within the file and not the range.

I'm always learning.

 

Yes, I agree with your assessment. The 24 bits vs 16 bits represent the level of detail represented by the numbers in the file. But like you, I will wait for an explanation of this.

 

BG

post #2269 of 5263
I simplify bits in my mind as noise floor. The more bits you have the more scope for lower noise floor and therefore greater dynamic range. If you take a 16 bit recording and play it out as 24 bit into a 24 bit dac you have basically added unnecessary headroom and therefore you can turn down software volume (reduce the bits) and it won't matter until you drop it down below 16bits (back to original file) even then you can see examples online of slowly dropping off the bits and It only becomes noisy and audible At about8-10 bits.
post #2270 of 5263
This video explains it better

http://m.youtube.com/watch?v=Zvireu2SGZM
post #2271 of 5263

So the 16-24 upscale isn't really scaling?  If it was 16 -> analog -> 24, then it would be scaling.  But since it's 16-24 digital scaling there is no way to scale proportionally digitally since it's in bits.  So that probably means the extra 8 bits on top of 16 are just padded(never listened in directly to the DAC line-out), not actually containing any information.  Therefore, it's safe to have the volume 16/24 = .66 or %67 or greater without performance hit.

 

Not sure how correct my assumptions are since you turn down the volume on the DAC, the amp output you can hear the volume decrease.  So, not sure if it's safe.


Edited by SilverEars - 3/27/14 at 5:55am
post #2272 of 5263
Well, that's cleared that up then 😆
post #2273 of 5263
Quote:
Originally Posted by SilverEars View Post
 

So the 16-24 upscale isn't really scaling?  If it was 16 -> analog -> 24, then it would be scaling.  But since it's 16-24 digital scaling there is no way to scale proportionally digitally since it's in bits.  So that probably means the extra 8 bits on top of 16 are just padded(never listened in directly to the DAC line-out), not actually containing any information.  Therefore, it's safe to have the volume 16/24 = .66 or %67 or greater without performance hit.

 

Not sure how correct my assumptions are since you turn down the volume on the DAC, the amp output you can hear the volume decrease.  So, not sure if it's safe.


Since there are 8 bits of volume, that means you can control volume using 256 values without degrading the quality.


Edited by BenF - 3/27/14 at 9:30am
post #2274 of 5263
Quote:
Originally Posted by r010159 View Post
 

 

Interesting. No offense, but I do not think it works this way. Something tells me this oversimplification has lead to a fallacy.  The volume level is mapped to more bits. But when turned to half volume, you are still dealing with half of the available information.  All the extra bits give you is a more graduated scale between no volume and full volume. This does not mean you just can throw away the bits to no effect, which is what you are implying.  

 

So there must be something I am not understanding of your explanation. Are you talking about 16-bits being mapped to the lowest order of 24-bits? Is that what is actually happening? This would mean the last part of the range of volume would make no audible difference at all. I do not think this is the case.

 

Like I said, I may be misunderstanding something here. :normal_smile :

 

BG

 

Hi,

 

when 16 bit audio data is mapped to 24 bit words this means multiplying by 256 or shifting left by 8, which is the same. The missing bits on the right hand side are set to 0.

 

EDIT: This multiplication is necessary in order to keep the volume equal for 16 bit and 24 bit mode. I one just kept the same numeric value in 24 bit as in 16 bit, the music would be inaudibly quiet. Thanks to user r010159 for pointing out that I was a bit quick here.

 

 

16 bit word:

 

              1001100110011001

 

24 bit word - high 16 bits same as before followed by 8 zero bits:

 

100110011001100100000000

 

If you're then halving the volume all words are divided by 2 or shifted to the right by 1 - left side is padded with zero bits again:

 

010011001100110010000000

 

So what you loose is one of the zero bits on the right hand side which were added by converting 16 to 24 bit.

 

 

In the case of native 24 bit material the case is a little bit different but not much:

 

100110011001100110011001

 

now we half the volume by dividing by 2 or shifting right 1 place - left side is padded with zero bits again:
 

010011001100110011001100

 

So we effectively lost the least significant bit on the right hand side which can be ignored since

 

 

a) the effective resolution of the best 24 bit DACs is only 21 bits and often less - so an error in the least significant bit will not be measurable

 

b) because human hearing can only resolve 16 bits of dynamic range anyways

 

EDIT: Please note that this argument is a bit simplified by assuming unsigned integers. In reality we need signed numbers and in 2's complement notation multiplication and left shifts are not equivalent. But in essence it's the same in 2's complement - namely for data scaled from 16 to 24 bits no data is lost by setting software volume to 50% and for 24 bit data the least significant bit is lost.

 

Joachim


Edited by jring - 3/28/14 at 1:45am
post #2275 of 5263
Quote:
Originally Posted by Zorrofox View Post

Hi, thanks for your input. So 24bit goes lower & higher in the frequency range than 16bit? I did not know that. I just assumed it referred to the amount of detail contained within the file and not the range.

I'm always learning.

 

Hi,

 

no, bit width has nothing to do with frequency range, it means how fine the differences in amplitude can be resolved.

 

Frequency range is governed by the sample rate via the nyquist frequency - the highest frequency which can be reconstructed from a sampled signal with sampling rate fS.

 

The nyquist frequency is 0.5 * fS or 22kHz for the usual CD sample rate of 44kHz. Since 22kHz is way above the limit of human hearing around 16kHz sampling rates of more than 44kHz are of dubious value for music meant to be listened to by humans - as opposed to dogs or bats.

 

Joachim


Edited by jring - 3/27/14 at 11:47am
post #2276 of 5263
Quote:
Originally Posted by jring View Post

Hi,

when 16 bit audio data is mapped to 24 bit words this means multiplying by 256 or shifting left by 8, which is the same. The missing bits on the right hand side are set to 0.


16 bit word:

              1001100110011001

24 bit word - high 16 bits same as before followed by 8 zero bits:

100110011001100100000000

[deleted]

You are placing the 16-bits left justified. The 16-bit number needs to be placed in the rightmost position to preserve the mathematical significance of the original 16-bit number. The volume operates on the number in this fashion. So should your analysis.

>>a) the effective resolution of the best 24 bit DACs is only 21 bits and often less - so an error in the least significant bit will not be measurable

You have just halved the volume. According to your analysis, this should make no audible difference. It does. Try it and see. IMO that is why it is best to keep the volume at the computer to full value. If it really does not make a difference, then why mess with the volume at all? What is the point in changing it from the computer instead of the amp?

BG
Edited by r010159 - 3/27/14 at 10:13am
post #2277 of 5263
Quote:
Originally Posted by r010159 View Post


You are placing the 16-bits left justified. The 16-bit number needs to be placed in the rightmost position to preserve the mathematical significance of the original 16-bit number. The volume operates on the number in this fashion. So should your analysis.

BG

You are right if you expect the 24 bit word to have the same numerical value as the 16 bit word. But max electrical amplitude of the DAC stays the same regardless of word width and must be reached at the max value of 16 bit or 24 bit data - so a multiplication must take place. If the 16 bits are put to right of the 24 bit word it is mathematically correct but the music would be inaudibly quiet.

 

Also it should be said that this example simplifies things a bit by assuming unsigned data - in 2's complement multiplication and shifting left are not equivalent so it cannot be visualized so easily but in essence things stay the same - namely for data scaled from 16 to 24 bits no data is lost by setting software volume to 50% and for 24 bit data the least significant bit is lost.

 

Joachim


Edited by jring - 3/27/14 at 10:14am
post #2278 of 5263
Quote:
Originally Posted by jring View Post

You are right if you expect the 24 bit word to have the same numerical value as the 16 bit word. But max electrical amplitude of the DAC stays the same regardless of word width and must be reached at the max value of 16 bit or 24 bit data - so a multiplication must take place. If the 16 bits are put to right of the 24 bit word it is mathematically correct but the music would be inaudibly quiet.

Also it should be said that this example simplifies things a bit by assuming unsigned data - in 2's complement multiplication and shifting left are not equivalent so it cannot be visualized so easily but in essence things stay the same - namely for data scaled from 16 to 24 bits no data is lost by setting software volume to 50% and for 24 bit data the least significant bit is lost.

Joachim

I see how you are thinking of this. Thanks for the discussion.
Edited by r010159 - 3/27/14 at 11:04am
post #2279 of 5263
Guys! Guys! I guess I should be ashamed but this is confusing. I think I'll just set the Mac volume as high as I can get away with whilst still having plenty of leeway on the hardware control. I've opted for 1x/3x and I'm using Q701's. Funny thing with them is that although they're 62Ohm impedance (which isn't particularly high) I read there's something else about them that makes them more demanding than it would appear.
post #2280 of 5263
Quote:
Originally Posted by Zorrofox View Post

Guys! Guys! I guess I should be ashamed but this is confusing. I think I'll just set the Mac volume as high as I can get away with whilst still having plenty of leeway on the hardware control. I've opted for 1x/3x and I'm using Q701's. Funny thing with them is that although they're 62Ohm impedance (which isn't particularly high) I read there's something else about them that makes them more demanding than it would appear.
Probably an amp with a high current output. I've read the same thing and I haven't found that to be the case, so I don't know what people are talking about. XD
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