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Author Topic: Digital Resoloution and bit depth  (Read 7238 times)

bobkatz

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Re: Digital Resoloution and bit depth
« Reply #30 on: February 13, 2005, 01:47:46 am »

kent walker wrote on Sat, 12 February 2005 21:52



Well, this is what Bob Katz writes in his mastering book anyway.  I've never read the claim that a 16 bit system can give a perceived dynamic range of 115 dB anywhere else, but I bet he has a source or a reason for saying that, maybe it is the noise shaping thing.  Thought I would check it against your findings.




Hi, guys. Didn't I write something like "it is possible to hear a test tone of as low as -115 dBFS in a properly-dithered 16 bit system".    That's the ABSOLUTE limit of conceivable audibility in a dithered 16 bit system. You can prove it yourself with a pair of headphones, an excellent, low-noise and linear D/A converter.

Whether this translates to 115 dB of true dynamic range is another question. It's probably more like 105 or so before the dither noise overcomes the signal. We're talking "very low" here...  ironically, though, I do believe that 24 bit masks the low level signal less than 16 bit, though it is an EXTREMELY subtle difference, and mostly makes a difference in cumulative processing. In other words, "start at 16 bit, process (at 24 to 48 bits), and end at 16 bit" sounds more veiled than "start at 24 bit, process (at 24 to 48 bits) and end up at 16 bit".

I've mastered some pretty transparent-sounding masters that originated in 16 bit by using noise shaped dither, but the number of "A pluses" I give to some of my "originally 16 bit sources" is far less than the number that my 24 bit sources have received. So, on the average, sounds better.

The irony is that 1/2" tape sounds great, and has a noise floor 20-30 dB noisier than 16 bit digital. I think I have some grasp on an explanation for this apparent contradiction, but would like to leave that for another time.

Regardless, to my ears, it's really a matter of noise accumulation, as we have seen that a properly dithered processing chain will not add quantization distortion.

Quote:



Are any 24 bit converters using dither?  I know many don't.  I am familliar with the limitations of dynamic range being 120 -something dB.  Just curious if any designers have found it worthwhile to add a little dither anyway.

-Kent




On the A to D converter side, I'm pretty certain that the laws of physics will take over and adequately self dither nearly every source we can conceive of to 21 or 22 bits, I'll bet my life. But if you were going for 20, 19, 18 or below, I'd recommend using proper dither in the converter, since, as Jay Frigoletto mentioned, it is highly unlikely that the "natural" noise sources will be random enough or have enough high frequency energy to totally and properly dither all the source to less than, say, 21 bits for the sake of argument.

But once you get past that and into processing, yup, it's desirable to dither every 48 bit (or 32 bit, or whatever) calculation upon reduction to 24. Is it REALLY REALLY important? Well, cumulatively it is. But the audibility of the quantization distortion from a single conversion from 48 to 24 is VERY VERY slight, and I would fail a blind test on that one.]
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howlback

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Re: Digital Resoloution and bit depth
« Reply #31 on: February 13, 2005, 02:49:49 am »

Thanks to everybody for the great replies!

I love to hear everybody's slightly different answers for finicky questions that many would dismiss as silly.

-best wishes,

Kent
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cerberus

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Re: Digital Resoloution and bit depth
« Reply #32 on: February 13, 2005, 10:06:18 am »

Nika Aldrich wrote on Sun, 13 February 2005 00:49

Of course, if the signal itself has enough noise present from natural sources then it doesn't have to be added first.


OK I think that is clear...and I think it means:  

Dither noise that already is added could theoretically be effective later in the signal chain; But after the whole signal passes another process, the noise becomes correlated with the process the same way the signal does, and is not noise anymore , so we need to add noise again ?


bobkatz wrote on Sun, 13 February 2005 01:47

... But the audibility of the quantization distortion from a single conversion from 48 to 24 is VERY VERY slight, and I would fail a blind test on that one.]


If you would fail a blind test then that is the answer i am looking for. I never fail the test when dither is involved.   So perhaps it is legitimate to always choose the distortion in these types of cases, because there is much less of it, including potential cumulative effects.



cerberus

bobkatz

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Re: Digital Resoloution and bit depth
« Reply #33 on: February 13, 2005, 10:39:48 am »

cerberus wrote on Sun, 13 February 2005 10:06

Nika Aldrich wrote on Sun, 13 February 2005 00:49

Of course, if the signal itself has enough noise present from natural sources then it doesn't have to be added first.


If you would fail a blind test then that is the answer i am looking for. I never fail the test when dither is involved.   So perhaps it is legitimate to always choose the distortion in these types of cases, because there is much less of it, including potential cumulative effects.

cerberus


Well, NO, that's not the case in my experience. You should ALWAYS choose to add the dither at the 24th bit if you want your sound to be subtly warmer. It took me 15 minutes with the most pristine material to be 100% sure (non-blind) that the 24 bit dithered choice sounded a bit warmer than the truncated choice. It only takes me 5 minutes or less to be sure about TWO generations of 24 bit truncation in a row versus two generations of 24 bit dithered. And so on.

I would vote on ALWAYS ADDING the dither at the 24th bit before truncating to 24. The noise of the dither is 144 dB down (actually -141, but who's counting), but if you DO NOT USE the DITHER, the distortion components due to NOT using the dither are somewhat higher than -144 dBFS and contain ugly harmonics that start to annoy the ears. It's just that at levels approaching the 24th bit, the accumulation of this distortion starts at a VERY subtle level that is usually masked by other noises in the chain.

But do not forget that each successive truncation increases the inharmonic distortion we call quantization distortion. The sound gets colder and colder with each successive truncation in the chain, even at 24 bits. It's just that the first time is so subtle that you would probably fail a blind test on it. How many truncations in a row? Before I hear it? Before the public notices it?

BK
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jfrigo

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Re: Digital Resoloution and bit depth
« Reply #34 on: February 13, 2005, 01:14:21 pm »

cerberus wrote on Sun, 13 February 2005 07:06


If you would fail a blind test then that is the answer i am looking for. I never fail the test when dither is involved.   So perhaps it is legitimate to always choose the distortion in these types of cases, because there is much less of it, including potential cumulative effects.



The distortion products are higher in level and correlated, so the dither is a more benign choice that will have less cumulative effect. Are you saying you can hear dither added in 24 bit reliably in blind testing? You can't be claiming this, and if you are, it should be easier to hear the distortion, so we're back to "dither is better than distortion."

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Bob Olhsson

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Re: Digital Resoloution and bit depth
« Reply #35 on: February 13, 2005, 02:53:24 pm »

You add 6dB of distortion with each successive undithered process while you only add 3dB of noise from each dithering.

cerberus

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Re: Digital Resoloution and bit depth
« Reply #36 on: February 13, 2005, 09:27:37 pm »

bobkatz wrote on Sun, 13 February 2005 10:39

.... You should ALWAYS choose to add the dither at the 24th bit if you want your sound to be subtly warmer.



But....  I already made it warmer. My mixes come out too dull then. To rectify this, I am bumping things up to 88.2khz now.   I don't like the very idea of the compromise you are implying. I want to be in control.


Quote:

It took me 15 minutes with the most pristine material to be 100% sure (non-blind) that the 24 bit dithered choice sounded a bit warmer than the truncated choice.

I think that whatever dither you use nowadays; I cannot afford it.  But I wish I could get a hold of the kind of [milder] dither that plug-in makers might be using for internal reductions.

Quote:

But do not forget that each successive truncation increases the inharmonic distortion we call quantization distortion. The sound gets colder and colder with each successive truncation in the chain, even at 24 bits. It's just that the first time is so subtle that you would probably fail a blind test on it. How many truncations in a row? Before I hear it? Before the public notices it?



I agree totally, I don't take issue with any of it at all. (...but how many dithers before you have had one too many ? )   I am feeling childish now because it seems I want a level of control that perhaps is impossible   I am frustrated now to hear that with all the great processors you might have access to, you use dither for "warming", which is basically a general application for vintage analog hardware.

Anyway another disturbing thought is that bit depth is about dynamics and the issue we are talking about manifests itself as a frequency issue. This makes it all a bit un-intuitive to reconcile the big picture and find the best strategy for processing.



jfrigo wrote on Sun, 13 February 2005 13:14

... Are you saying you can hear dither added in 24 bit reliably in blind testing?


No, that is too general a statement. And of course I do not claim to hear dither itself, only the effect of dithers I have used in my own studio on music. I prefer to use L2 or L3 for brickwall limiting, but every time I use it, it quantizes it's output to a minimum of 24 bits.  I can hear all the dither and noise shaping options in these plug-ins and also from UV-22 on my system.  L2 and L3 both use 9th order noise shaping, but I don't like it. I also don't like UV-22. POWr and Megabit Max are available to me, but I do not know how to use them with L2 or L3, and I don't really think I like noise shaping at all !

Bob Katz mentioned here me a few months ago that Waves type 2 is not random enough, I think.  But for me Type 1 is not warm at all, it makes extra brightness to my ears, I tried it again because BK's criticism of Waves Type 2 dither was pointed, but I do not want any extra "HF excitement" or "percieved dynamics" in my mixes to come from dither.  Listeners are supposed to hear that effect in some dithers, so they -should- be able to be heard if they work as advertised.  

Quote:

 You can't be claiming this, and if you are, it should be easier to hear the distortion, so we're back to "dither is better than distortion."



A full scale 24 bit signal is equal to a full scale 32 bit signal. So in that hypothetically perfect case, there is no distortion to hear.  I am suggesting that if the signal is within 6 db of full scale at 24 bits, then the distortion product could be lower than the dither noise, in fact infinitely lower.  (I have never done a controlled experiment with 48 signals, so I don't know if my observations for 32 bit float apply to 48 bit fixed or not, but float is very different than fixed here, and perhaps that is where we differ, I do not use a TDM system, and most people here do...)  I suggest that this applies in practice. It explains the results of my own experiments from which I became interested enough in this subject matter to try and learn more.


cerberus

Bob Olhsson

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Re: Digital Resoloution and bit depth
« Reply #37 on: February 14, 2005, 01:37:47 am »

Mixes that are too dull would probably benefit a lot more from a bit of HF eq. than from using distortion to add sizzle.

cerberus

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Re: Digital Resoloution and bit depth
« Reply #38 on: February 14, 2005, 01:48:30 pm »

Bob Olhsson wrote on Mon, 14 February 2005 01:37

Mixes that are too dull would probably benefit a lot more from a bit of HF eq. than from using distortion to add sizzle.


That is a good way to put it, certainly we don't want sizzle from -that- kind of distortion.

My aversion to boost EQ must be holding me back; but this could be a good place to make exception... So your advice, which may seem obvious to some, is a help to me.

cerberus

cerberus

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Re: Digital Resoloution and bit depth
« Reply #39 on: March 17, 2005, 04:04:04 am »

The answer to me is clear now, Mix at a high enough sample rate and everything will be more natural sounding by the time you get to 16/44.1.  Every decent digital box is oversampling.. Why it took me so long to figure this out; dunno, pretty obvious actually.... Perhaps I wanted to think in terms of -more- plug-ins; the first thing I did with the  G5 was to see how many reverbs....  Thanks to all who offered advice to me here, especially Bob Ohlsonn.


cerberus
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