Can we hear the bottom bits of 24?

[beefkabob]

No, simply experienced. A normalized 24 bit track downsampled and dithered to 16 bits will sound exactly the same as the normalized 24 bit file. However, having well over 20 db of headroom makes postproduction so much easier, you can pull up the quiet bits, compress the dynamic peaks that won't work in a domestic environments, have the noise floor inaudible. Otherwise, high bit rates are mostly a waste of data. Not only can we not hear a full 24 bits of dynamic range, so far nothing actually reaches 24 bits on account of the self-noise of the analog output. Of course, the self-noise of human hearing is much worse than that.

I think I misunderstood him. I thought he was complaining about loudness mastered into music, getting rid of dynamic range.

 

[MRC01]

Wait for the brain sensor helmet. Have a young kid with perfect hearing wear it and record the neural activity from his ears when listening to music. Then copy that recording and play it back on your own brain sensor helmet, bypassing your ears and directing stimulating your brain in the same way. It will bring you to tears of joy as you experience the perfect hearing acuity of childhood while being able to appreciate the music with the wisdom of your years.

 

[MakeMineVinyl]

We cannot get anywhere near the 24 bit level with acoustic music unless we record in an anechoic chamber using dead musicians.

 

[earlevel]

Despite what, IIRC, Bob Katz wrote in his book, there's no way this stuff would be audible. Unless you're deliberately leaving 90dB of headroom and expect massive boost on playback.

I don't know what he wrote in his book. But we did have a chat on FB years ago, and it was on a similar topic as this. He said that—contemporaneously, he said he checked on it between our messages—he confirmed that he could hear the lsb of 24-bit audio through his console. That is, just the naked lsb, not listening to music. Now, I had said "without using digital gain", so I don't think he intentionally did anything like that. I asked him for his method, and he explained how he hooked it up and verified it. It wasn't detailed enough that I could be sure of what he was doing, so I left it at that.

I highly respect Bob Katz, I'm not mentioning the above to say he is flawed. I'm only saying that there may be reasons why he feels that he can hear the lsb with no doubt in his mind that he might be imagining it. It seems the only explanation is that he performed a flawed experiment that convinced him, but I just don't know the details.

 

[pozz]

Now, that last bit is tantalizing, isn't it? Seems like it should be its own thread to muse on. It seems like we might have to wait for a direct connection to the brain, a la Neuromancer. If we record anything (via mics, playing electric instruments), room temperature is unavoidable, so we're either looking at algorithmic noise reduction or generating music in the digital domain, to start with 24-bit-pure sound. Then, chilling amp (and speakers I suppose) is asking a bit much, so I guess we're going for something close to ear buds or headphones (and I guess drivers might need chilling?). Then our ears would still be ears, of course, but it's a fun thought process whether it's even possible (let alone practical) to get to that point. Um, I'm holding out for Neuromancer

The simstim tech?

In this book: https://www.routledge.com/Sound-System-Engineering/Davis-Patronis-Brown/p/book/9780240818467

One of the chapters speculates that this is the next frontier.

 

[bravomail]

Those will drown in noise with absolute certainty. If not by the DAC itself then by the amp following it and even more so by our rather flawed hearing abilities.

24 bit format is handy for recording because you can have loads of headroom to capture peaks (just to limit/compress them later on in production).
A 24 bit DAC is also handy when using digital volume control.

Plenty of research has been done about audibility levels and with various types of jitter being used.
Besides test tones is not equal to recorded music and noise in actual recordings greatly exceeds any 24 bit errors.

best DACs will resolve 20bits only. 4 bits r for volume and studio edits. 32 bit therefore is better

 

[pozz]

We cannot get anywhere near the 24 bit level with acoustic music unless we record in an anechoic chamber using dead musicians.

It's Redbook, but close still: https://www.discogs.com/release/8306193-Various-Anechoic-Orchestral-Music-Recording

I don't know what he wrote in his book. But we did have a chat on FB years ago, and it was on a similar topic as this. He said that—contemporaneously, he said he checked on it between our messages—he confirmed that he could hear the lsb of 24-bit audio through his console. That is, just the naked lsb, not listening to music. Now, I had said "without using digital gain", so I don't think he intentionally did anything like that. I asked him for his method, and he explained how he hooked it up and verified it. It wasn't detailed enough that I could be sure of what he was doing, so I left it at that.

I highly respect Bob Katz, I'm not mentioning the above to say he is flawed. I'm only saying that there may be reasons why he feels that he can hear the lsb with no doubt in his mind that he might be imagining it. It seems the only explanation is that he performed a flawed experiment that convinced him, but I just don't know the details.

I have it and will glance at that section again when I have time.

 

[tecnogadget]

Since you asked for technical replies, this book will clear you mind and answer all your questions. 24bits has benefits for the recording/production environment purposes, after that 16bit is enough for delivery format. Cheers

 

[TimF]

The technical question vs. the practical question. There may be people, or other animals, with exceptional hearing and who similarly possess exception qualities of attention so that they can exercise and explore the limits of their perception. Under specific conditions with an absolute minimum of background noise using methodology that we consider scientific we likely could accurately determine the extreme limits of technology in relation to the extreme limits of human perception. We don't listen to music in anechoic chambers, nor do we listen to music with singular and strict dedication of attention as that kind of focus can be maintained only so long. The international celebrity musical performers are not just one in a million, they are one in 20 or one in 40 million. They are abnormalities almost. It may be that extremes of technology and extremes of persons with exceptional preceptive abilities can do quite unusual feats. So what? Like I need a 500 horse power automobile? Like I need to downhill ski on skis the same as those who do the Giant Slalom in the Olympics.

 

[earlevel]

The technical question vs. the practical question. There may be people, or other animals, with exceptional hearing and who similarly possess exception qualities of attention so that they can exercise and explore the limits of their perception. Under specific conditions with an absolute minimum of background noise using methodology that we consider scientific we likely could accurately determine the extreme limits of technology in relation to the extreme limits of human perception. We don't listen to music in anechoic chambers, nor do we listen to music with singular and strict dedication of attention as that kind of focus can be maintained only so long. The international celebrity musical performers are not just one in a million, they are one in 20 or one in 40 million. They are abnormalities almost. It may be that extremes of technology and extremes of persons with exceptional preceptive abilities can do quite unusual feats. So what? Like I need a 500 horse power automobile? Like I need to downhill ski on skis the same as those who do the Giant Slalom in the Olympics.

Interesting points, for sure, a lot to discuss. But I'd say there are fundamental limitations on two basic front:

The electronics side (Johnson noise, shot noise...).

The human side. Well, obviously it's reasonable to argue that the electronics is a sufficiently limiting factor, and it doesn't matter if there is one super-human who can outdo our hearing expectations. But setting that aside, there are intuitive limits on hearing as well. For example:

There has to be enough sound pressure to deflect the eardrum. Other masses too, but if the ear drum doesn't deflect, it's a non-starter. My only point here is that it's intuitive that there is some minimum. Then we can talk about exactly what it might be.

And, the body itself makes noise—again, I'm just making intuitive arguments, I don't know the physiology well enough, but I've read that if human hearing was much better, we'd be kept awake by the blood flowing through out veins. I think maybe the brain does or could ignore some things, but my point here is that even humans have a noise floor, even if they could find a noise-free room.

Besides having a floor, there is a ceiling. And it doesn't do any good to speculate that some super-human might have a far greater ceiling than normal people. For instance, it's no good arguing that someone in the world might happily listen to music at 140 dB SPL, because WTF would they be listening on . That means, without question, that the lowest bit is far, far below 0 dB SPL. Meaning a super-human would require extreme downward sensitivity (in a battle with the noise floors), that upward dynamic range won't come into play significantly.

So while it's not possible to rule out that some human has far better hearing than most (there is no "black swan" way of disproving that), we can be confident that between the noise floors of electronics and humans, not to mention practical environments, there must certainly be some limitation, and it seems to be within the 24-bit range and not outside of it.

PS—Just making deductions based on my limit knowledge of hearing, would love to hear thoughts from others

 

[Robin L]

We cannot get anywhere near the 24 bit level with acoustic music unless we record in an anechoic chamber using dead musicians.

This.

 

[Tangband]

I need to recalibrate my head, in a space where people are open to discussing technical aspects of audio and questioning whether it's really possible to hear something, a opposed to feeling insulted that anyone should question it. Not to disparage a useful discussion board, I think "GS" is close enough for those curious, then no one need ask. But this is more about checking out this space and people.

I questioned the ability to hear the bottom couple of bits of 24-bit. I'll briefly give the reason, for context, but I don't want to dwell on it: The typically way music is recorded results in a multitrack mixdown and likely involves processing in the digital domain. Even if we were able to record perfectly, if we want to produce a 24-bit resulting audio file, we need to either truncate which produces error correlated to the signal (not a good idea in general), or we add a little dither noise to then truncate, resulting in a similar error size but lack of correlation—the error broadband noise, a constant hiss. With normal dither, the means the difference between the original "perfect" signal and the 24-bit dithered output is ± 1 lsb. So that's by I say the last couple of bits—it's pointless to move up from that and question three or four bits.

For now, I won't go into physical limits of the electronics (Johnson and shot noise, etc.), or the dynamic range of the ear (not my expertise, but it seems if we set our maximum listening volume to a tolerable level, according to typical hearing info it seems like ~140 dB SPL down from that would be not easy to hear, to understate it).

So, I'm asking whether people think the lowest couple of bits of 24-bit audio can be heard, and why or why not. Related to what I've already said, such questions might be whether we can tell the difference between the original ("perfect") audio and the truncated or dithered versions, between 24-bit truncated and dithered versions, or even the naked nulls (the difference) between any of these. Or simply hear a known test signal of that level.

5-bit sample sweep tone
16-bit sample sweep tone
24-bit sample sweep tone

24-bit is the one you want to listen to, but you should familiarize yourself with the tone by hearing the 5-bit so you know what to listen for. The 16-bit is there too, for fun.

I'll link the an old article containing them, because you'll probably want to download at the least the 24-bit so you can play or view outside of your browser—the direct links might be awkward to download from, depending on browser: Perspective on dither

I just want to see what people have to say, maybe discuss.

24 bit is good because :

1. When doing recordings of live events, you must have a marginal of about -10 dB in the A/D . So there is 10 dB resolution gone. More resolution is always better later in the production chain when the recording is mixed, using reverb, eq, compressors and such .

2. Digital volume controls need more than 20 bits to regulate the volume without truncation of 16 bit material. At least in theory.

 

[KSTR]

I agree, but I'll add for the discussion that there is a fundamental limit of how close we can get, because there is a limit on the lowest noise floor possible. Since there is also a (slightly loose) limit on the highest voltage a DAC can put out, both in the sense of being realizable and in being compatible with other audio gear, that puts the last bits under that noise floor, unavoidably. (Just making an assertion, not laying the law—I'm totally open to anyone discussing why that might not be true.)

Mojo Audio has an interesting paper (not assuming anything one way or another about their gear, I don't know, but they aren't cheap so I give them props fro honesty):

The 24-Bit Delusion

Key conclusion: According to the experts who manufacture the finest DAC chips, resistors, and power regulators, there is theoretically no way to make electronics that are capable of discerning much greater than a 20-bit resolution (120dB dynamic range). Any company who claims 24-bit resolution from their DAC is simply full of [edit for forum decency: poo]. Oh they can decode 24-bits, because 24-bits does exist on the digital side, but the analog output stage in the world's best DACs are not capable of resolving much more than 20-bits of dynamic range.

Well, there are ways to get beyond 20 bit signal-to-noise ratio with today's parts and techniques (noise being here the RMS noise level in the audio band) but those are brute-force approaches: If you summed the output of, say 100 AK4493's or similar, this will reduce all uncorrelated analog and digital noise by 10x, so a 20dB improvement which would get us close to bit 24. With some tricks you can also make any signal-correlated digital noise to average out as well. OK, 100 pcs. would be insane, but 30 might be on the edge of feasibility and give some 14dB noise improvement, obtaining ~22 bits of SNR.

But I fail to see an actual need for this in home HiFi. We simply don't need a full 24 bit dynamic range. We welcome more than 16 for final playback as seen by the DAC chip, though, once some processing of 16bit sources takes place (EQ, digital room correction, digital volume control -- within limits).

Some extreme studio scenarios might benefit from a significantly lower noise, as would some some instrumentation and measurement applications but in general this is overambitiuos here as well.

What's more important IMHO is to have more products with clever adaptive gain staging in the DAC output stages ganged with the native digital volume control, like RME did with their Auto Reference Level feature. This makes output SNR practically independent of output level for the majority of required leveling tasks.

 

[SKBubba]

At this point I'm happy to be able to hear 20k bits of FR and 8 bits of DR. And the Mrs. won't even allow me to play it loud enough to hear that.

 

[Robin L]

My question would be: what is the self-noise of the human hearing apparatus? We already know that this is variable, that with those with tinnitus have elevated levels of self noise. Has this parameter been measured? I've seen fletcher-munson curves showing limits of audibility depending on frequency. Maybe this should be [or already is] a thread here. I'm older, know that my hearing ability is compromised. When it's late at night, and there's nothing going on, I can hear some low-level hiss emanating from my nervous system. I'm sure I'm not alone. And I know that my audio gear, when there's pauses between tracks, has less self-noise than my ears at 4:00 in the morning.

 

[sarumbear]

I need to recalibrate my head, in a space where people are open to discussing technical aspects of audio and questioning whether it's really possible to hear something, a opposed to feeling insulted that anyone should question it. Not to disparage a useful discussion board, I think "GS" is close enough for those curious, then no one need ask. But this is more about checking out this space and people.

I questioned the ability to hear the bottom couple of bits of 24-bit. I'll briefly give the reason, for context, but I don't want to dwell on it: The typically way music is recorded results in a multitrack mixdown and likely involves processing in the digital domain. Even if we were able to record perfectly, if we want to produce a 24-bit resulting audio file, we need to either truncate which produces error correlated to the signal (not a good idea in general), or we add a little dither noise to then truncate, resulting in a similar error size but lack of correlation—the error broadband noise, a constant hiss. With normal dither, the means the difference between the original "perfect" signal and the 24-bit dithered output is ± 1 lsb. So that's by I say the last couple of bits—it's pointless to move up from that and question three or four bits.

For now, I won't go into physical limits of the electronics (Johnson and shot noise, etc.), or the dynamic range of the ear (not my expertise, but it seems if we set our maximum listening volume to a tolerable level, according to typical hearing info it seems like ~140 dB SPL down from that would be not easy to hear, to understate it).

So, I'm asking whether people think the lowest couple of bits of 24-bit audio can be heard, and why or why not. Related to what I've already said, such questions might be whether we can tell the difference between the original ("perfect") audio and the truncated or dithered versions, between 24-bit truncated and dithered versions, or even the naked nulls (the difference) between any of these. Or simply hear a known test signal of that level.

5-bit sample sweep tone
16-bit sample sweep tone
24-bit sample sweep tone

24-bit is the one you want to listen to, but you should familiarize yourself with the tone by hearing the 5-bit so you know what to listen for. The 16-bit is there too, for fun.

I'll link the an old article containing them, because you'll probably want to download at the least the 24-bit so you can play or view outside of your browser—the direct links might be awkward to download from, depending on browser: Perspective on dither

I just want to see what people have to say, maybe discuss.

What is the point of your test when there are no 24-bit DACs yet?

 

[sarumbear]

We cannot get anywhere near the 24 bit level with acoustic music unless we record in an anechoic chamber using dead musicians.

What about the 1812 Overture with a real canon?

 

[earlevel]

Well, there are ways to get beyond 20 bit signal-to-noise ratio with today's parts and techniques (noise being here the RMS noise level in the audio band) but those are brute-force approaches: If you summed the output of, say 100 AK4493's or similar, this will reduce all uncorrelated analog and digital noise by 10x, so a 20dB improvement which would get us close to bit 24. With some tricks you can also make any signal-correlated digital noise to average out as well. OK, 100 pcs. would be insane, but 30 might be on the edge of feasibility and give some 14dB noise improvement, obtaining ~22 bits of SNR.

Thanks for reminding me of this, I had a feeling I was missing something besides going to a higher rate.

 

[sarumbear]

24 bit is good because :

1. When doing recordings of live events, you must have a marginal of about -10 dB in the A/D . So there is 10 dB resolution gone. More resolution is always better later in the production chain when the recording is mixed, using reverb, eq, compressors and such .

2. Digital volume controls need more than 20 bits to regulate the volume without truncation of 16 bit material. At least in theory.

We are talking about audio signal, not internal processing, which is mostly 32-bit floating anyway.

 

[earlevel]

What is the point of your test when there are 24-bit DACs yet?

My test—you mean the 24-bit file. Not really a test, just a reference.

Some people (from discussing on other boards) are 100% certain they can hear the bottom bit, some aren't sure, but they know that skilled recording engineers have said they can—it's just a reference that people can play with for their own interest. Same reason I included 16. Nothing to be proved, just a known reference to play with privately.

BTW, references are good for something: One discussion maybe two years ago included a guy who claimed that we really only needed 12-bit audio. Fundamentally, the guy knew what he was talking about, and we agreed on a number of things, but I thought he took it too far with 12-bit. (16-bit, you've got an argument, even 14-bit for consumer is not unreasonable to argue, but 12-bit, nope—for tones maybe, not music.) I don't think I gave him a tone, I think I told him to maybe truncate to 12-bit and null, or whatever. He actually came back and said, "oops, I didn't realize the 12-bit noise floor was that loud", and modified his thinking a little.

So, I do think it's good to have something for listening perspective. For instance, for me, if I listen to the 16-bit tone, or the residual from nulling 16-bit dithered or truncated audio, at moderate to low listening levels it's amazing how good 16-bit is. Though if I crank to loud but not unreasonable listening levels, there are the flaws. Nothing proven, just for perspective.

One problem I come across often, though, is some people will concede that the 24-bit tone and 24-bit truncated/dithered nulls probably can't be heard, yet truly believe that if that tiny error level is added to perfect music, somehow the soundstage will collapse, etc.