PHILIPS RED BOOK

[Wombat]

Is there a definitive rejection of Philips Red Book specification for well made CDs audio output performance compared to higher sampling rate produced discs?

It seems to me that Red Book CDs are only limited by the material embedded, in terms of human hearing.

Subjective replies to be backed up with hard facts, please.

 

[Blumlein 88]

I am not sure I understand what you are asking. Are you asking which aspects of the Red Book standard are inadequate for better sound that higher sampling rates can provide?

 

[Wombat]

Are the limits of Red Book CDs AUDIBLY surpassed by other formats? Subjective responses backed up by objective measurements, please.

 

[Cosmik]

'Red Book' presumably contains lots of highly technical stuff related to optical encoding, etc. that is not directly related to sample rate and bit depth. Is it really just a question of whether 44.1 kHz / 16 bit is adequate?

 

[Soniclife]

I think there are 2 questions here.
1) Is 16/44.1 enough to fully capture what humans can hear.
2) Is downsampling from higher rates music was created in to 16/44 audible.

I think the answer to 1 is yes, not seen anything to contradict that. But 2 is a maybe, but very small.

 

[Jakob1863]

It´s still an open question; Joshuas Reiss´s meta- analysis provided some evidence that 16/44.1 might not be sufficient, but further research is needed.

Btw, the Red Book constraints does not prevent anyone from producing audio CD´s with content that most likely can´t be reproduced properly, but i assume that Wombat wanted to exclude those by the "well made CDs" .

 

[Speedskater]

I don't think that most of us have seen the contents of the 'Red Book'.

 

[sergeauckland]

Many years ago, I remember reading a report in a Technical Trade magazine, so not a HiFi Rag, (Trade Rags are that much better!) that the Sony PCM-F1 passed a straight-wire bypass test under blind evaluation conditions. This was the PCM-F1 used ADC-DAC and switched in and out of an analogue monitoring chain, where its presence was undetectable.

I have done similar tests myself with a variety of ADCs and DACs, and have come to the same conclusion, that 16bit 44.1kHz sampling is quite sufficient for transparency, and consequently perfectly adequate for domestic music distribution. Greater bit depths or higher sampling rates won't in itself improve the perceived sound.

Back in the late 1990s I worked for a company manufacturing Audio Test and Measurement equipment, and we introduced a high quality ADC/DAC unit which could be used both as a studio converter and as a front-end for older analogue-only measuring equipment to provide some digital capability. The standard test was to use the unit as an ADC/DAC pair in an analogue environment or as a DAC/ADC pair in a digital environment, and both should be transparent, which of course they were, even at 16 bits and 44.1kHz. The unit had various bit depths and sample rates available, and it could at a push be used as a sample-rate converter going via analogue.

At the Scalford HiFi show a few years ago, the person I was helping showed the effect of reducing the bit depth from 24 bits down to about 8 bits, but with proper dither and noise-shaping. We had quite a few who were convinced we were pulling some sort of trick when the bit depth, which many thought 16 bits to be inadequate, was dropped further and further down, and with some sorts of music even down to 8 bits wasn't audible, although by then the noise floor had come up too high for transparency.

Consequently, I remain totally unconvinced that anything more than 16 bits at 44.1 sampling is needed as a distribution format for home use.

S

 

[amirm]

I think there are 2 questions here.
1) Is 16/44.1 enough to fully capture what humans can hear.
2) Is downsampling from higher rates music was created in to 16/44 audible.

#1 can be shown to not be true unless you use noise-shaping. And noise shaping is best done at higher sampling rates.

Briefly, the desired dynamic range for a noise-free channel needs to convey 120 db of dynamic range (based on highest loudness in live presentations and threshold of hearing). Doing so with dither at CD rates doesn't work since we are limited to 94 db or so. Noise shaping where we push the noise to higher frequencies helps to do this.

Problem is that you don't know if noise shaping was used to produce the content. Indeed I think its usage is rare.

A better solution then is to have a format with 20 bits of resolution. Since that is an oddball number, might as well go for 24 bit. This way we are not at the mercy of anyone recording music to understand and use noise shaping.

 

[amirm]

BTW, this topic has been extensively researched by Fielder and published in a number of his AES/J. AES papers. He goes through the entire chain of recording and playback, and combined with listening tests showing threshold of hearing, computes the 120 db number I stated.

 

[sergeauckland]

#1 can be shown to not be true unless you use noise-shaping. And noise shaping is best done at higher sampling rates.

Briefly, the desired dynamic range for a noise-free channel needs to convey 120 db of dynamic range (based on highest loudness in live presentations and threshold of hearing). Doing so with dither at CD rates doesn't work since we are limited to 94 db or so. Noise shaping where we push the noise to higher frequencies helps to do this.

Problem is that you don't know if noise shaping was used to produce the content. Indeed I think its usage is rare.

A better solution then is to have a format with 20 bits of resolution. Since that is an oddball number, might as well go for 24 bit. This way we are not at the mercy of anyone recording music to understand and use noise shaping.

Although, is a 94dB dynamic range in any way inadequate? Considering the S/N ratio of mic amps, and the S/N ratio of recording venues, what's actually being recorded once one gets down to below about -80dB? Aircon noise, traffic rumble, mic amp and mixing desk noise, not a lot of actual musical value.

I fully accept that 16 bit/44.1kHz is inadequate for recording and mixing, except for the simplest of recording techniques like 'purist' crossed-pair or perhaps the Decca Tree. Recordings which will have a great deal of manipulation done is far better done at higher sample rates and bit depths, but as a distribution format for putting music into people's homes, I don't see it as lacking anything.

S.

 

[Cosmik]

Although, is a 94dB dynamic range in any way inadequate? Considering the S/N ratio of mic amps, and the S/N ratio of recording venues, what's actually being recorded once one gets down to below about -80dB? Aircon noise, traffic rumble, mic amp and mixing desk noise, not a lot of actual musical value.

I fully accept that 16 bit/44.1kHz is inadequate for recording and mixing, except for the simplest of recording techniques like 'purist' crossed-pair or perhaps the Decca Tree. Recordings which will have a great deal of manipulation done is far better done at higher sample rates and bit depths, but as a distribution format for putting music into people's homes, I don't see it as lacking anything.

S.

Yes, if it can be shown that the bit depth of the digital playback system is never the limiting factor, then the theoretical 120dB requirement becomes moot.

 

[amirm]

Although, is a 94dB dynamic range in any way inadequate? Considering the S/N ratio of mic amps, and the S/N ratio of recording venues, what's actually being recorded once one gets down to below about -80dB? Aircon noise, traffic rumble, mic amp and mixing desk noise, not a lot of actual musical value.

That is the study from Fielder which shows that to not be a limitation. I wrote a digest of his research for the playback side in this article: https://audiosciencereview.com/forum/index.php?threads/dynamic-range-how-quiet-is-quiet.14/

In a nutshell, we need to look at the spectrum of noise. When we do, the SPL noise numbers that we think are too high, turn out to not be the case where our hearing is most sensitive.

Furthermore, we are able to hear noise coming out of speakers or a band playing, well below room noise. The directionality of the noise that way is key, versus diffused one in the environment.

He also examines the limits of microphones, speakers, amplifiers, etc. The paper is quite long, is peer reviewed, and has some 60 references. It is very hard to shoot holes in it.

Here are some sample data from his paper, Dynamic-Range Issues in the Modern Digital Audio Environment*
LOUIS D. FIELDER, AES Fellow

So here we see despite these recording venues having noise floors at low frequencies as high as 45 db, they are all pretty close or beat threshold of hearing. They do so because their noise level is as low at 0 db or even lower at mid-frequencies where we are most sensitive.

This is peak playback levels in same and other venues across larger number and genre of performances:

So we see that peak is above 120 db even for non-amplified music in some cases (black bars). So if we take 0 db for the lowest level and 120 db for highest, we arrive at 120 db dynamic range requirement.

Here we see that threshold of hearing white noise -- the kind created by equipment/channel -- is actually lower than threshold of hearing that is based on detection of tones:

Here is the data on microphones:

On and on. Here is the abstract summarizing it:

 

[Jakob1863]

I don't think that most of us have seen the contents of the 'Red Book'.

Obviously, due to the fact that there always was a signed NDA required (still today!) it is not surprising that most haven´t seen it.
Therefore i thought it might be interesting that ....

 

[sergeauckland]

Yes, but the requirement may be to record a dynamic range of 120dB, not to reproduce a dynamic range of 120dB. No domestic system could do that, and still have neighbours.

Not many homes can support a dynamic range of much more than 60dB or so, perhaps 70dB, so the 90+ dB range of CD is already far greater than is needed for home use. That's my point.
S.

 

[amirm]

Yes, but the requirement may be to record a dynamic range of 120dB, not to reproduce a dynamic range of 120dB. No domestic system could do that, and still have neighbours.

All the numbers here are peak SPL. Average SPL that we are all familiar with is quite a bit lower (as much as 10 db). Specialized meters are used for the study. For the purposes of recording, we must use peak numbers, not slow-averaging as is used for noise measurements and such.

 

[sergeauckland]

All the numbers here are peak SPL. Average SPL that we are all familiar with is quite a bit lower (as much as 10 db). Specialized meters are used for the study. For the purposes of recording, we must use peak numbers, not slow-averaging as is used for noise measurements and such.

Sorry, I don't see how that's relevant. Peak SPL is Peak SPL.

If you want to record an orchestra that has a peak at 127dBSPL as the graph above shows, it just needs a microphone that won't distort at those levels, which proper Pro mikes as mentioned can handle happily. Capturing the very quiet levels, then may well require a dynamic range of 120dB at the time of recording.

However, when it comes to reproducing that recording at home, there's no possibility of generating a peak SPL of 127dB, unless one's home is a studio. So, the peak level at home will perhaps be 100dB, 110dB if one's really being 'enthusiastic' With a background level of 20-40dB SPL at home, that gives a dynamic range of perhaps 90dB maximum, more typically 70dB. That makes CD's range already adequate. Bearing in mind further than the S/N ratio of most power amps is under 100dB, I can't see any good reason why we need more than CD already provides.

There may be a few people, with scant regard for their hearing or the peace and tranquility of their neighbours who might want to make more noise, but should music companies pander to those?

S.

 

[Cosmik]

So in summary: if I want to reproduce the sound of a 747 taking off (or whatever) in my living room at the absolute loudness it occurred, I need high res digital in order for my system not to contribute any perceptible noise when the sound stops - assuming it was recorded in a silent environment with the best microphones and pre-amps.

But if I only want to reproduce it at the level of a jackhammer (or whatever sound is 20-30dB lower down on the illustrated dB chart!) then CD will not be the limiting factor.

 

[Cosmik]

I think the paper kind of demonstrates the point that CD is pretty much adequate, in that it has to get every link in a long chain at the absolute limits of what is possible in order to get the 120dB requirement. The reality will be that 99.999% of recordings coupled with listeners and their listening environments won't come anywhere near it.

 

[sergeauckland]

I think the paper kind of demonstrates the point that CD is pretty much adequate, in that it has to get every link in a long chain at the absolute limits of what is possible in order to get the 120dB requirement. The reality will be that 99.999% of recordings coupled with listeners and their listening environments won't come anywhere near it.

Considering the dynamic range of many CDs these days is virtually nil anyway, I'd be happy if they went to the dynamic range of a non-Dolbied cassette, let alone 120dB.

I've looked at the levels of a number of my recent acquisitions, and the time they spend at 0dBFS, with very obvious flat-topping shows that Dynamic Range is not what's driving the music business.
S.