How many bits, how fast, just how much resolution is enough?

[gmgraves]

It all started way back in about 1982 with the arrival of CDs originally providing a resolution or data rate of 44.1khz/16 bit. Now we can obtain or generate music files at a resolution of 384khz/24 bit or higher.

 

I've personally gotten caught up in the rush to higher resolution and have upgraded several times to be able to play back 384khz/24bit files and also getting into DSD64 and now DSD128. I'm not sure

 

Advances in electronics will, probably, allow for almost limitless increases in resolution and storage space to house those huge files is exceedingly low but at what point does the human ear stop hearing any improvement? Where will it end?

 

Theoretically, we're there. 24-bit resolution already gives a noise floor that's so far below the threshold of human hearing, as to be totally irrelevant. Not only can humans not hear noise that far down, but it is also more quiet than any analog stage that would follow the D/A conversion. Resolution? 384 KHz sampling rate gives a frequency response flat out to 192 KHz! Even if we allow that some instruments produce sounds quite a bit in excess of 20KHz, none are likely to produce RF, which is what 192KHz is converging on. So, theoretically, noise levels that can't be heard, frequency response that's serious overkil, and vanishing levels of distortion, even in soft musical passages, how much more is necessary?

[gmgraves]

I've as of yet to find anything in our industry to impugn this presentation on why 16/44.1 is good as it gets for us.

 

24/192 Music Downloads are Very Silly Indeed

 

You're overlooking the fact that digital is not very good at either end of the dynamic range spectrum. It doesn't handle peaks very well because they can often exceed 0 Vu which means that the system runs out of bits, and that's a no-no. This potential condition requires that the recordist back-off on overall record level to avoid overmodulating. This means that in a 16-bit system, low level passages are down in the mud where only one or two bits are being "exercised" causing massive distortion + noise and guaranteeing that ambience gets severely truncated. This can be mitigated somewhat by adding small amounts of random noise (called dithering) to the signal, but that's "cheating". Best of add more "bits". With 24 or 32-bit encoding one can avoid overmodulating the system by backing off on the record level without fear that your low-level will be shifted down in the 1 to 2 bit level or lower (where the signal is simply truncated).

[gmgraves]

That is something that you could comment to Monty on. He seems perfectly capable of answering it.

 

Dithering is not cheating. It's managing the known noise component so you can shift it to the in-audible end of the spectrum and filter it out.

Uh, that's the reason the word cheating is in quotes. Yes, it is introducing low level noise to linearize low level signals to keep from a situation where only one or two of the LSBs is being manipulated by changing the PCM to virtual PWM. But it's a bandaid when compared to actually adding more bits.

[gmgraves]

That's it.

Masking through dither, even when used below the audible threshold, is still a crutch.

Alternatively one could always turn down the volume or open the windows to increase the noise in the room.

R

 

That's what I meant when I said it's "cheating". I.E. it doesn't solve the problem, it merely masks it, like a bandaid on a cut finger.

 

It's interesting how dithering was discovered. Digital mastering engineers kept wondering, in the early days of CD, why CDs mastered from analog tape sounded better than the latest DDD recordings, since both went through the same digital equipment. Turned out that the tape hiss from the analog recoding was acting like an inadvertent dithering signal. The engineers, once having discovered this, experimented with reducing the noise level to find the right balance between adding enough noise to act as a dither, but not so much as to be blatantly audible. Once they found that happy medium, the rest was recording history. It is interesting to note that as long as recording engineers use enough record level to keep at least 4-bits below the level of the quietest passages in one's recording, and 4-bits above the loudest passage (in other words use 16-bits within a 24-bit "envelope") 24 and 32-bit recording don't need dither, until down-converting the file to Red Book for CD mastering.

[gmgraves]

Meyer, E. B. and D. R. Moran. 2007. Audibility of a CD-Standard A/D/A Loop Inserted into High-Resolution Audio Playback. JAES 55(9): September 2007

 

Abstract:

Claims both published and anecdotal are regularly made for audibly superior sound quality for two-channel audio encoded with longer word lengths and/or at higher sampling rates than the 16-bit/44.1-kHz CD standard. The authors report on a series of double-blind tests comparing the analog output of high-resolution players playing high-resolution recordings with the same signal passed through a 16-bit/44.1-kHz "bottleneck." The tests were conducted for over a year using different systems and a variety of subjects. The systems included expensive professional monitors and one high-end system with electrostatic loudspeakers and expensive components and cables. The subjects included professional recording engineers, students in a university recording program, and dedicated audiophiles. The test results show that the CD-quality A/D/A loop was undetectable at normal-to-loud listening levels, by any of the subjects, on any of the playback systems. The noise of the CD-quality loop was audible only at very elevated levels.

 

The Meyer/Moran paper is always trotted out to reinforce the myth that Red Book is "perfect sound forever" and high-resolution formats are unnecessary overkill. It has since been soundly debunked numerous times with criticism of the methodology the equipment, and listening environments as well as the type of listening subjects used.

[gmgraves]

where can I read your published comments? I assume you are a Fellow of the AES, right?

 

While these are not "my published comments" (just as the Abstract quote posted by you (Ralf11) aren't yours....) they are links to others:

[h=3]Meyer and Moran debunked by Meridian's Robert Stuart - Computer ...[/h]

 

[h=3]The Controversial Meyer and Moran Study: A Fresh Look[/h]

[h=3]Meyer and Moran: Let's Change the Focus | Real HD-Audio[/h]

[h=3]SA-CD.net - Debunking Meyer and Moran[/h]

[h=3]AES Journal Forum » Audibility of a CD-Standard A/DA/A Loop ... (this one might cost money to read. It is AES)[/h]

 

[h=3]Thoughts on Meyer/Moran SACD/DVD-A vs. CD audio study? - AVS Forum[/h]

[h=3]Meyer & Moran Updated: Proof that CD audio isn't transparent ...[/h]

[h=3]Art Dudley | Stereophile.com[/h]

This series of links should give you a enough info on both sides of the argument to make an informed decision on the value of the Meyer/Moran study.

[gmgraves]

Neither it seems can my ears come up with a sonic comparison.

 

I wonder if someone will chime in with something really solid that'll start me wondering if my brain has decided that hires is pointless and expectation bias is confirming my preference for Redbook?

 

What kind of music do you listen to? I ask because I notice the difference mostly (but not exclusively) on low level material. If one listens mostly to pop and rock where the dynamic range of the music itself ranges from loud, to louder and loudest, or, as in most modern CDs has had what dynamic range there is compressed to within an inch of its life, there isn't much in the way of low-level detail or large room ambience. Here, the difference between 24-bit and 16-bit is really profound. While my listening choice is mostly classical, I also like jazz and listen to it a lot. I have to admit that on most jazz recordings, I find it often difficult to impossible to tell 16-bit Red Book from 24-bit. There just isn't a lot of low-level material or hall ambience in that genre either to show off the advantages of the higher bit rate. Of course, if one compares the Red Book version directly with a real 24-bit (or DSD) version, you should notice a general increase in cleanliness of the higher sample rate version that one might not notice without a direct comparison. Even then, there are a lot of variables in a commercial release of either, that some might argue could account for that difference.

;-)

... seriously though, if someone gave me my entire library in 24 bit (if that was possible) I'd obviously accept the gift and use it... but I'd never contemplate doing any work myself to get (any of) my library in hires. On my system that would seem a waste of time.

 

Well, the difference between a Red Book CD of a recording and a high-res version of same certainly is not on the order of the difference between a master tape and the LP made from it, so the high-res version most assuredly doesn't make the Red Book version unlistenable. Enjoy.

[gmgraves]

Thx, unfortunately only one of those is a peer-reviewed publication. They could still be correct, but your claims are not supported, esp. by the Stereopile 'thing'. I'll take a look at the one AES later on...

The links were not provided to sway you either way. As my last line says "This series of links should give you enough info on both sides of the argument to make an informed decision on the value of the Meyer/Moran study."

Is that the same Bob Stuart that everybody dumps on for trying to foist MQA on us? ;]

Yes.

Similarly, there some studies showing that mp3 files cannot be distinguished from redbook. It costs me nothing to use Apple Lossless instead tho (well, ok - I guess it cost me a little more for a higher capacity iPhone).

 

Actually, at bit rates of 192 kbps and higher it is extremely difficult to tell the difference between Red Book and MP3. Listen, some Saturday evening, to the live Boston Symphony Orchestra webcast from WCRB in Boston or listen, on demand to the past concerts as listed on the page referenced below:

 

The Boston Symphony Orchestra | 99.5 WCRB

 

These are 192 kbps and sound damn good on speakers. I do hear occasional compression artifacts on headphones though, but then, I know what compression artifacts sound like. These broadcasts are virtually indistinguishable from 16-bit LPCM as on a CD.

 

I'm fine with using higher bit rates or depth as long as I don't have to pay a lot for it.

 

Reasonable response

[gmgraves]

re: it's a fact that a 44.1KHz sample rate is mathematically adequate to reproduce all audible frequencies.

No doubt about that. But it isn't all about frequency response. There are other criteria that define fidelity.

[gmgraves]

Hi George,

I don't do classical very often, but given how everything else sounds I don't see why it would be represented poorly.

I think I gave my explanation for that.

I think the key thing appears to be how well the DAC does redbook... the VEGA seems to excel in this area and that's why I'm enjoying it so much - and as I've voiced before, the system just seems to be so much more forgiving that any other system/config that I had before.

 

By definition, of a DAC sounds great doing 24-bit, it will do 16-bit just as well.

 

I will continue to enjoy... but won't rule out hires in case I hear something I've been missing.;-)

That's perfectly OK it's (still) a free country

[gmgraves]

Re: comparing classical... see if you can do the same experiment on an Auralic VEGA?

 

Unfortunately, I don't have an Auralic Vega. I have a Schiit Modi2 Multibit and am waiting on delivery of a Schiit Yggdrasil multi-bit true ladder DAC. As far as I can see, the Vega is a Delta-Sigma DAC in which I currently have no interest. On the other hand, my comment to which you are responding, is not an experiment, it's just fact. A 24 (or 32)-bit DAC, if you play a 16-bit Red Book file through it, will actually sound better than through a 16-bit DAC because the filtering on the higher-bit DAC is better and most modern DACs seem to up-convert 16-bit material to 24-bit anyway.

 

... if someone want to make available 2 files of classical 16/44 and hires, I'll try it out.

 

Probably not a reliable test. You don't know what the difference is between the mastering moves applied to the 16-bit and the 24-bit versions. I have a number of "hybrid" SACDs and in all of them, the Red Book and the SACD layer's versions of the same performance sound significantly different. I also have several BMG (RCA) hybrid discs and their JVC XRCD (Red Book) counterparts. Not only does the Red Book layer on the hybrid disc sound different from the SACD layer, but the JVC XRCD sounds different from the Red Book layer on the SACD! They should sound the same, but they don't!. In fact, in all cases, the XRCD version not only sounds different from SACD remastering, but it sounds BETTER and by a long shot! No, in remastering for different formats, there's too much slip twixt the cup and the lip to make any experiment like you propose a valid comparison.

 

Luckily the UK is also a free country.

:-)

 

Yes the UK is free, in as much as any of us are free anymore. I fear that the experiment of Democracy is quickly dying everywhere it's practiced. As the world becomes more and more crowded, freedoms will become more and more curtailed. In many places some freedoms are already given only lip service, and don't actually exist like they used to.

[gmgraves]

Can You show (or at least tell) how the filtering differs when it is feed from 16/44 or 24/44 signal?

 

You misunderstand me, I think. A 24-bit DAC's filter doesn't perform differently when processing 16-bit/44.1 KHz material than it does when it is decoding 24-bit/96 or 192 KHz material, it handles 16-bit as if it were 24-bit. With 16-bit/44.1 KHz material, the sample rate (44.1 KHz) must roll-off very steeply above 22.5 KHz to satisfy the Nyquist theorem. Such so-called "brick wall" filters can cause problems like phase shift in the audible band. When a 16-bit/44.1 KHz source (such as a CD) is played on a DAC that can handle 24-bit/96 or 192 KHz files, the sampling frequency is much higher than 44.1 KHz by twice or even 4X (in a 192 KHz capable DAC). This moves the sampling rate far outside the 22.5 KHz bandwidth of a16-bit/44.1 KHz file (such as a CD). There are several different ways to do this, but the result is that the "Q", or steepness of the filter can be much more gentle, and therefore does not introduce the phase shift and other anomalies caused by steep, brick-wall filters required to get the audio signal down by at least -20 dB by the time the sampling frequency is reached (at least 2X the "Nyquest" frequency [or top frequency being quantized], in this case 22.5 KHz). I hope this clears up the confusion. It's a bit oversimplified as an explanation, but just remember that the further the DAC's sampling rate is from the highest frequency in which one is interested (again, 22.5 KHz for Red Book CD), the better the sound. Oh, yes, one other thing. 16-bit sounds better through a 24-bit DAC than it does through a 16-bit DAC due to the filtering employed, but also because no commercial 16-bit DACs have 16-bit linearity, just as no 24-bit DAC gas 24-bit linearity. BUT a 24-bit DAC does have 16-bit linearity (at least) which lowers quantization error of 16-bit material substantially. But I never said or inferred that 16-bit through a 24-bit DAC sounds better than 24-bit through the same DAC, which I believe you think I was saying.

[gmgraves]

Uh, I think you're confused. Any 44 kHz signal needs a sharp filter, even if the DAC is capable of higher sample rates.

 

Does that not depend on whether or not up-sampling is used on the 44.1 KHz. Don't most modern 24-bit DACs do that? I see that I failed to make that distinction, in which case, mia culpa. Thank you for pointing that out Mansr!

[gmgraves]

Albert Einstein had a long running argument with Abe lincoln, but Heisenburg lost it somewhere

 

Heisenburg was confused.