Is the dynamic range of CD sufficient?

Al M.

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On the Trinity DAC thread (Forum: Digital) we had a brief discussion about the question if the 16/44 CD format is even theoretically sufficient, apart from the technical problems that have been tough to solve but now have resulted in implementations which, three decades after the introduction of CD, show that CD is really a true high-resolution medium indeed.

On the Trinity DAC thread (p. 47 ff.) some people including me have argued that, yes, the 16/44 CD format is at least theoretically sufficient, but others have argued that the 16 bit dynamic range and high frequency issues, quite apart from practical filtering problems, indeed pose theoretical problems. I had contended that the dynamic range is more than sufficient, since you can't get below something like 25 dB background noise (very quiet living room, or basically empty concert hall except musicians) and an orchestra only on very rare occasions reaches 110 dB (which is screamingly loud). This would make for a maximal dynamic range for orchestral music of about 85 dB (at 110 dB - 25 dB). A similar dynamic range for orchestra (around 70-80 dB) has been cited on several websites, including on the Wikipedia page on dynamic range with a book citation on this. For recording that dynamic range, the dynamic range of 96 dB of 16/44 CD is more than sufficient.

Yet even so, trying orchestra at maximum live levels at home in everyday listening situations is not recommended, since 110 dB is close to ear-damaging levels even for just short amounts of time (I never go beyond 95-97 dB for short orchestral climaxes at home, which is really really loud, and usually I keep max levels somewhat below that -- after 2 minutes of the final brass chorale of Bruckner's Fifth Symphony at 95-97 dB, reproduced without appreciable distortion, I already feel pressure in my ears). So I would say that makes even an 85 dB dynamic range unnecessary in home listening situations. Your noise floor in your listening room is a minimum of 25 dB -- at least it is around 25 dB in mine, in a very quiet neighborhood, with sound-suppressing windows and no electrical gear except the stereo system, thus under really optimal circumstances. So for practical listening situations that would make for around a 95 dB - 25 dB = 70 dB effectively needed dynamic range.

Those thoughts about dynamic range are basically mirrored and expanded upon in the following article:

http://kenrockwell.com/audio/why-cds-sound-great.htm

Quote from the article:

16 Bits: More than enough

While professional editing, mixing, processing, equalizing and level shifting usually use more data bits for computation (24 bits linear, 32-bit floating point or now 48-bit linear), 16 bits is more than enough for unlimited fidelity as a release format.

The reason we use more bits in production is so we can create and preserve a true 16 bits through the whole process after all the truncation and rounding and nastier stuff that goes on between the microphone and your CD.

16 bits is more than enough, and with popular music today, even 8 bits is more than enough.

How is this?

16 bits have a signal to noise ratio of 98 dB (theoretical SNR = (bits x 6.0206) + 1.72 dB). That doesn't sound like much compared to 24 bits theoretical 146 dB, but realize that a library's background noise is about 35 dB SPL. Your house probably isn't any quieter. A full symphony orchestra giving it all it's got (ƒƒƒƒ) peaks at about 104 dB SPL. Let's give the orchestra 105 dB, and 105 dB - 35 dB = only 70 dB real dynamic range if you brought the orchestra into your home.

Supposing we recorded on the moon in a pressurized tent with no background noise? Well, the self-noise of most recording studio microphones is about 16 dB SPL equivalent input noise, or in other words, microphones aren't any quieter than about 16 dB SPL anyway.
Even though some people can hear to 0 dB SPL, we're always hearing background noise if we shut up and listen. It takes a lot of money to build an NC 25 or NC 15 studio, in other words, a recording studio with about a 15 dB or 25 dB SPL background noise. Even in an NC 15 studio, 105 - 15 = 90 dB SPL, well within the range of real 16-bit systems, if you record it well.

16 bits was chosen because it has more than enough range to hold all music. I know; I was doing 16-bit recording back in 1981 before the CD came out, and my recordings would have their levels carefully set so the loudest peak of the entire concert hit about -3 dB FS, and leaving it running after the audience left and the hall was empty, you can still bring up the playback gain and hear a perfectly silent recording of the air conditioning noise in the hall. The world just doesn't get quiet or loud enough to need more than 16 bits as a release format, if it's recorded well.

There is no such thing as a real 24-bit audio DAC or ADC. Look at the specs, and you'll never see a 144 dB SNR spec; all audio 24-bit converters do have 24 bits wiggling, but the least few LSBs are just noise. There is plenty of 24-bit and higher DSP, which is good to keep the 16-bits we need clean, but you're never getting 24 real bits of analog audio in or out of the system. It's a good thing you can't; 140 dB SPL is the threshold of instant deafness, and if you lift the gain enough to hear a real 24-bit noise floor at say 20 dB SPL in a very quiet studio, maximum output would be 20 + 144 = 164 dB SPL, or 4 dB over the threshold of death. Yes, 160 dB SPL kills.

But wait, there's more. 98 dB is the theoretical SNR. With dither, we still can hear pure undistorted signals down into the noise for at least another 10 or 20 dB. While a typical real-world 16-bit system's SNR might be 92 dB, we can hear tones down to -100 dB FS easily. That's over 100 dB of dynamic range in real 16-bit systems.

There's even more than that! By the 1990s, people learned how to "noise shape" the dither to push it up mostly to 15 kHz and above, so it became much less audible, but just as effective as regular dither. These systems made the noise much less audible. These systems are also called Super Bit Mapping (SBM) by Sony and UV22 byApogee; they claimed 22-bit effective SNRs with 16-bit systems. They didn't really work that well, but they did make our 16-bit system even better than it was. These clever sorts of dither are still used today for 16-bit releases.

That's right: done right, 16 bits is way, way more than enough for any sort of music. Once you've heard it done right, you'll realize any noise you here out of a CD is due to sloppy recordings (usually sloppy level settings someplace in the chain), not the CD medium itself.

(End Quote.)

The article also has interesting things to say about SACD and loudness wars.

***

I think the first two paragraphs quoted from the article are important for those worrying about data loss in 16/44:

While professional editing, mixing, processing, equalizing and level shifting usually use more data bits for computation (24 bits linear, 32-bit floating point or now 48-bit linear), 16 bits is more than enough for unlimited fidelity as a release format.

The reason we use more bits in production is so we can create and preserve a true 16 bits through the whole process after all the truncation and rounding and nastier stuff that goes on between the microphone and your CD.


So what do you think, is 16 bit enough or not?
 

Alrainbow

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Great read. I have read other articles regarding the same topic. Generally people in this hobby want equipment to be able perform at levels if heard would deafen or even kill us . I have myself tried to hear the change from 96 to 192
And I cannot with any consistency make the correct choice. This is why 16/88.2 red book is most likely all would ever need.

Thanks

Al
 

microstrip

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Al.M,

There is very little material available at 24/44.1 , I doubt that most of us have significant experience with it.

We had a thread in WBF in the past where Bruce_B made available some tracks with cymbals with different bit depths and sample rates - I remember that there was an audible difference between 16 and 24 bit, but I do not remember if there was a 24/44.1 version or only at higher sampling rates, but I think they are not available at his ftp server any more.

We can make fantastic mathematical and theoretical statements about bit depths and dynamics, but in the end it is the practical implementation that defines the sound quality. According to maths and electronics we do not need more than an average $100 CD player to have all the dynamics of CDs, but IMHO some players are much more dynamic than others. Do you still remember the evolution of DACs in CD players? They started with 14 bits oversampling x4, then 16 bits, 18 bits, 20 bits and now 24 bits. Did we really need them? IMHO, yes.
 

Al M.

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We can make fantastic mathematical and theoretical statements about bit depths and dynamics, but in the end it is the practical implementation that defines the sound quality. According to maths and electronics we do not need more than an average $100 CD player to have all the dynamics of CDs, but IMHO some players are much more dynamic than others. Do you still remember the evolution of DACs in CD players? They started with 14 bits oversampling x4, then 16 bits, 18 bits, 20 bits and now 24 bits. Did we really need them? IMHO, yes.

Yes, some players are much more dynamic than others, and in my first paragraph I made the distinction between the theory of 16/44 CD and its technical implementations. The question at hand is whether the 16/44 medium is inherently flawed, as many have contended over the decades, and that in principle you can never get optimal resolution out of it. I would say now that I have learned a bit more about the medium that, no, in principle it should be sufficient, and we should not need 24/192 or similar.

Having said that, indeed the technical implementation is a different matter, and it is apparently much harder to get proper resolution out of 16/44 on the practical technical level than from so-called hi-res formats. Yet I get what I would consider fantastic resolution out of my Berkeley DAC. While evidently there are several other valid technical approaches, it greatly upsamples everything in order to get the technical implementation right -- but the original information is obviously still just at 16/44.

Since I don't think CD is inherently flawed I believe that, instead of chasing the current hi-res craze, manufacturers instead should put more energy into getting the CD medium right. After all, that's where all the music is, and that should matter to audiophiles who love music and not just its sound. What's the real-world relevance of hi-res media where there is hardly any music available on? None.

***

And apparently it can be done, albeit with top sound currently at high cost. As Peter Breuninger states in his review at AV showrooms about the flagship MBL combo:

"The MBL 1611F D/A Converter and the MBL 1621F Transport represent a state-of-the-art attack on the best sound that digital audio reproduction offers today. Together as a set they produce the most analog like sound this audio reviewer has yet to experience from a digital front end. Ordinary 44.1 kHz Redbook CDs become as smooth as SACDs with the air and life you would expect from vinyl. In fact, the MBL combination is as satisfying as one of the best analog systems in the world… the Onedof turntable, Triplaner, Ikeda, and Zuzma 4Point arms, Ikeda 9TT and Phase Tech P-1G cartridges into the outstanding Wyetech Ruby Phono Stage. That’s a $170,000 analog system!

The MBL 1611F D/A Converter and 1621F Transport… it’s analog on a silver disc!"

From:
http://www.avshowrooms.com/MBL_DAC_Transport.html
 

amirm

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I actually wrote an article on this very topic :). Here it is: http://www.madronadigital.com/Library/RoomDynamicRange.html

Quick message is that ambient noise measurements are not correct basis for the lower floor. We need to perform a spectrum analysis and match it to our hearing.

On noise shaping and dither, yes, that can give us more headroom. Problem is, folks don't know how to do that right at production side necessary. So the best answer in my opinion is for us to get the 24-bit files in our homes. If we then think 16 bits is enough, we can properly convert them. And if we don't, then we can stay with 24 bits.
 

esldude

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And what about microphones. Self noise in mics is often 15-20 db. As we can hear into noise perhaps 20 db, that might get you close to 0 db. But how many recordings are done in an area with that low a noise level. I don't know of any.

I would say one factor that makes 24 bit worthwhile, even if one has near SOTA equipment to really have 20 bit resolution in the analog world is when one uses DSP for room correction or digital crossovers. The extra bits allow processing that doesn't raise noise levels or effects to the point of audibility.

Various hirez material sourced from the finest analog tape won't stress 16 bit. It is simply too noisy. I have seen some fully digital hirez that will possibly exceed the 16 bit limit above 3-4 khz. Though it too is in the -70 db range at lower frequencies. And even if the recording is that good, I still don't think you can hear it in your home. Quiet levels at the bottom of 16 bit are audibly silent, even if quieter in a measured sense you don't hear total silence as more silent with 24 bit noise levels.

But with the possibility of DSP involved, though I doubt we lose anything at 16, but I also figure there is little reason not to do everything at 24 bit. Memory, disk drive space and processing power are such that the extra data is pretty much a non-factor to deal with. I do think 48 khz is probably plenty and that higher rates are a waste of space and processing power.

As always quality mastering is the biggest issue. Superbly done 16/44 is a joy and lousy 24/192 is still lousy.
 
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JackD201

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I'm along Amir's lines on the topic. Take a native 24bit file and play it down converted yourself. That should give you an idea as to what is better. It's such an easy thing to do these days. Even iTunes can do it for you.
 

dallasjustice

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I agree with Amir. We can't disconnect the recording/processing chain from the final product we hear. So 24 bit may be needed to avoid a down conversion from 24 to 16, if that's really audible.

In theory, digitally recorded red book is hi resolution.
 

Sonus

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I think the answer is easy, the day i would be able to listen to a concert at home with the same fidelity as going to a real performance then i'll say the spec is sufficient.
You will argue that the problem is not with the media, i say prove it.
 

Phelonious Ponk

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I think the answer is easy, the day i would be able to listen to a concert at home with the same fidelity as going to a real performance then i'll say the spec is sufficient.
You will argue that the problem is not with the media, i say prove it.

Are we talking about total fidelity relative to live performance? I thought we were talking about dynamic range.

Tim
 

LL21

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I think the answer is easy, the day i would be able to listen to a concert at home with the same fidelity as going to a real performance then i'll say the spec is sufficient.
You will argue that the problem is not with the media, i say prove it.

Are we talking about total fidelity relative to live performance? I thought we were talking about dynamic range.

Tim

Agree with Tim...I can hardly believe that dynamic range alone spells the difference between a live performance and a sound system reproduction of the same performance. I think that the question was solely about dynamic range of CD being sufficient to capture the relevant dynamic range of an actual performance. Kinda similar to asking if 20hz to 20khz is sufficient to capture the frequency scale of a live performance.
 

Sonus

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Are we talking about total fidelity relative to live performance? I thought we were talking about dynamic range.

Tim

I knew you'd say that, tell me how do you know the DR of a CD is sufficient? when it is clear that it can't capture the DR of a live performance.(Classical)
 

LL21

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I knew you'd say that, tell me how do you know the DR of a CD is sufficient? when it is clear that it can't capture the DR of a live performance.(Classical)

Wouldn't the recording engineers know simply by measuring the decibels in the room what the dynamic range is of what they are recording? In other words, if the performance is driving from a low of 37db to a peak of 110db, then that's the range. The CD either can or cannot capture it. The question of whether or not ANY playback (using CD or any other medium) can capture live is based on a gazillion other factors.
 

Sonus

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Wouldn't the recording engineers know simply by measuring the decibels in the room what the dynamic range is of what they are recording? In other words, if the performance is driving from a low of 37db to a peak of 110db, then that's the range. The CD either can or cannot capture it. The question of whether or not ANY playback (using CD or any other medium) can capture live is based on a gazillion other factors.

I don't understand why we need to complicate simple things, the answer to the question "Is the dynamic range of CD sufficient?" should be relatively easy.
The dynamic range of CD is sufficient only if it can capture the full dynamic range of a live performance of any kind.
Yes or No?

To my understanding the answer is no.
 

Phelonious Ponk

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I knew you'd say that, tell me how do you know the DR of a CD is sufficient? when it is clear that it can't capture the DR of a live performance.(Classical)

Well the range of a CD is from lower than I can hear above the noise in the quietest room in my house, to louder than I'd ever care to listen so, of course it is sufficient.

Tim
 

LL21

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I don't understand why we need to complicate simple things, the answer to the question "Is the dynamic range of CD sufficient?" should be relatively easy.
The dynamic range of CD is sufficient only if it can capture the full dynamic range of a live performance of any kind.
Yes or No?

To my understanding the answer is no.

from the post below, it would seem 16 bit is more than enough.

"...98 dB is the theoretical SNR. With dither, we still can hear pure undistorted signals down into the noise for at least another 10 or 20 dB. While a typical real-world 16-bit system's SNR might be 92 dB, we can hear tones down to -100 dB FS easily. That's over 100 dB of dynamic range in real 16-bit systems..."

Seems like plenty of range when even a quiet auditorium is probably 35db or higher, no? Sorry if I am not getting something...please explain. thanks.
 

Sonus

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from the post below, it would seem 16 bit is more than enough.

"...98 dB is the theoretical SNR. With dither, we still can hear pure undistorted signals down into the noise for at least another 10 or 20 dB. While a typical real-world 16-bit system's SNR might be 92 dB, we can hear tones down to -100 dB FS easily. That's over 100 dB of dynamic range in real 16-bit systems..."

Seems like plenty of range when even a quiet auditorium is probably 35db or higher, no? Sorry if I am not getting something...please explain. thanks.

Well, first my room has a 24db noise floor. I know people with 20DB noise floor rooms.
A live Symphony can cross 120db easily for short period of times (in big venus).

120db-20db=100db vs the 96DB of a CD.

BTW:
The dynamic range of human hearing is roughly 140 dB, in my opinion this is the DR value we should strive for.
 

microstrip

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I actually wrote an article on this very topic :). Here it is: http://www.madronadigital.com/Library/RoomDynamicRange.html

Quick message is that ambient noise measurements are not correct basis for the lower floor. We need to perform a spectrum analysis and match it to our hearing.

On noise shaping and dither, yes, that can give us more headroom. Problem is, folks don't know how to do that right at production side necessary. So the best answer in my opinion is for us to get the 24-bit files in our homes. If we then think 16 bits is enough, we can properly convert them. And if we don't, then we can stay with 24 bits.

Excellent advice. Unfortunately there is no recipe to add 8 bits of true information to thousands of existing recordings ...
 

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