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75.38.28.100
I havent figured out how much 2 channel audio information that can be put on a blu ray. Im not sure but I think the disc capacity is 20 MB.Maybe 64/1028?
Follow Ups:
Tim de Paravicini said in 1982 that 400 khz 24 bit was the magic combination for digital audio. The technology to realize this goal is certainly there...whether he or anyone else attempts it remains to be seen.
Well, it is certainly possible to decimate a sigma delta bitstream generated by an ADC to 400kHz 24-bit.However, some would argue that it's better just to retain the original bitstream and send that directly to the DAC.
That was the original premise behind DSD and SA-CD. Of course, modulation rates now exceed 2.8MHz, so DSD (at least at 1X) is no longer state of the art.
I'm just spouting numbers and phrases at this point but here is another article of interest...and a format that would definitely make use of the space on a blue-ray disc.
It's meant to be an intermediate editing format.The actual resolution is always constrained by the original sigma delta bitstream. DXD is a way of converting this bitstream into a representation that is easily editable, and for that purpose it's fine.
Another example of an intermediate editing format that's not intended for consumer delivery is DSD Wide.
But everytime you convert from one format to another (ie. DSD to DXD and back to DSD) you lose a tiny bit of resolution/information.
Now if DXD becomes widely accepted (currently it's only used by Merging in Pyramix) then potentially yes it would be nice to put it on bluray or whatever and avoid the conversion back to DSD. That is of course assuming that DACs out there can play it.
uncompressed super hd video? 3D holographic video? i'm sure someone will figure out a new format for these.
you mean the capacity is 20 GB, right?24/176 would be great but again the final result is due not only to the sampling frequency and bit depth but to the surrounding audio chain (whether it is all high resolution enough to take advantage of everything).
the laser pickup is a weak link, as RSchulz says.
master analog tape played back on analog tape machines is pretty damn good, problem is, large scale distribution of such formats is not practical.
keep in mind too that these companies (i.e., sony) are primarily in it to make money, not to give you good accurate sound in your home.
I think the analogy of comparing bits to dynamic range is not right thinking. If you have a -90db signal at 16 bits there are 3 steps....this is obviously low res.....with 24 bits it looks more like a true sine wave.....32 bit would give more steps and therefore more resolution....also the same would apply in some way with sampling frequency....I personally don't care if a DAC measures 100dB or 120db dynamic range wideband....which is how they are tested....in fact, I remove most, if not all analog filters so you cannot even see a -90 signal on the scope....so, does this mean that I have less than 90db dynamic range....absolutely not! You do not listen wide band....your ears only hear to 20K. So the noise above 20K is really not that important unless there is so much of it that it folds down to where you can hear it.....some DACs and DSD output (because DSD is a one bit signal and puts out lots of out of band noise) cannot be used without at least one pole of analog filter or otherwise you will actually hear hiss coming from the source....obviously, this hiss is interfering with the resolution....but if you do not hear hiss, you will get better (more transparent) sound with less output filtering. This I have tested over and over again on various machines (DACS and players) for years.Here is what I think would make great digital sound. Record at least 24/192 onto fixed memory....play back on fixed memory with a battery powered fixed memory player using Superclock technology and NO digital filter and NO analog filter....you would need to use PCM 1704s (a bunch in parallel, natch) or such DACs for this. It would not measure that well without any filtering, but I bet it would sound so transparent, you would care less. Today there are several non filter DACs (either/or digital filter or analog filter) that many today swear sound much better than oversampling and analog filtering.....and this is with 16/44 sources.....imagine this with 24/192 and battery power and Superclock and fixed memory.....I mean, I cannot stand to listen to a CD/SACD/DVD-A unless I black it, sand it, Auric Illuminate it, demagnetize it and Ionoclast it....this is how bad the laser thang is.....fixed memory...all the way folks.....fixed memory...fixed memory...I want it.
Sony has a professional digital recorder that records on fixed memory and runs on batteries....only 24/96 and does have digital and analog filters....but I bet a live 24/96 recording made on this $1800 machine and played back out of it would be mind blowing. Laser reading sucks big time.
Most ADCs these days are based on a sigma delta design, which is typically a bitstream running at approx 6Mbps these days. This is then decimated to the desired output resolution. The quality of the bitstream is the constraint, and is a constant no matter what the output resolution is.Even at 44.1k, the bitstream generates only about 20-21 bits of resolution. At higher sampling rates, there's even less resolution (because your are "spreading" the original bitstream thinner). If you don't believe me, check out the data sheets for most flagship ADCs - they tend to show higher noise for higher sampling rates.
Some people tend to refer to resolutions like 192kHz 24-bits as "marketing" numbers :-)
HowdyIn PCM you don't need more than 24 bits (144 dB) and it's arguable whether you need more than, say 96, 192 or 384 K samples/sec. 24 bits covers individual molecules hitting the ear drum to jet engines at X feet. Also, tho undoubtedly things will get better, it's hard to build better than 20 bit ADCs and DACs.
Or am I misunderstanding what you mean by 32/512 and 64/1028?
-Ted
Hi Ted,
32 bit/512KHZ sample rate ( like CD is 16/44 and dvd 24/96). Im just fantasizing about these numbers and they may not be technically possible.I am interested in seeing what the maximum resolution is possible(probably better than DVD-A or SACD).
HowdyThen, yep, you don't need better than 24 bits and I stand by the rest of my post as far as PCM is concerned.
Personally I'm a fan of SACD (DSD) and I think you might be better off using DSD or twice or four times the sample rate.
Don't forget that lossless compression will add some capacity...
With greater resolution comes more problems. The sound floor of amplifiers can now be reached. Who wants to listen to your amplifier imperfections with even greater clarity. As an audiologist I can tell you that if your older than 6, have lived in the real world you no longer have the ears to tell the difference between 20 or 24 bit word length. I'm sure someone will market greater word length and higher sampling frequency but it becomes a numbers game and not one to benefit the listener. Back in the 1970's when the receiver wars were going on total harmonic distortion greater than .1% was considered bad. Your ears were hard pressed to hear .5% THD from 20-20KHZ but if it was greater than .1% you had a bad product.
16-bit data has a theoretical dynamic range of 96 dB. 20-bit data has a theoretical dynamic range of 120 dB. 24-bit data has a theoretical dynamic range of 144 dB. Most electronics produce too much noise to even realize the full dynamic potential of 20-bit playback, let alone 24. The LSBs in both cases are likely to contain mostly ambient noise.This is also why applying dither noise isn't necessary when truncating data of 24 bits or more down to 20 bits or more. The ambient noise alone would be adequate for such application.
The dynamic range listed for n number of bits assumes a minimum quantization of 1dB, no? 20log(10)[2^16]=96.3dB.Has it been established that 1dB is enough? At all frequencies? Established with a modern state of the art system with audiophiles? (not blindfolded psychology students from 1960)
There have been complaints about low level resolution since the arrival of CD. By your reasoning, one might think that electronics (and speakers) would produce too much noise and distortion to be able to hear the relative noise and distortion of cables.
"There have been complaints about low level resolution since the arrival of CD."I've been one of those stating such complaints....
"By your reasoning, one might think that electronics (and speakers) would produce too much noise and distortion to be able to hear the relative noise and distortion of cables."
I'm not sure what you mean by "cables"..... I do think with digital amplifiers, the loss of low-level resolution makes differences in interconnect cables less-noticeable. And in some cases unnoticeable.
The point I was trying to make was the obsession with wordlength being rendered baseless by the mere fact that once the audio data exceeds 20 bits, the need to apply noise for dithering goes away because the residual noise of the electronics would doing so anyway. Unless the S/N ratio of the electronics upstream to the A/D conversion was better than -110 dB.
I see. Thanks for explaining. By cables I meant analog interconnects that we hear as quiet or relatively distortion free compared to other cables. We hear differences despite the extemely low distortion figures and noise.Pardon my more general rant about audibility. (Besides, it's explained above that 1970s receivers are more than good enough.)
HowdyNope, no correlation.
I'm not even sure where you might get that idea. Here's a guess: Since 20 log base 10 of 2 is 6.02059991328 we often use the rule of thumb that it's exactly 6. Hence it takes more than 24 bits before it's wrong rounded off (24 * 6 is 144 and 20 log (2^24) is approx 144.494397919 which is still 144 when rounded. However none of this has any bearing on "minimum quantization".
What I was doing was taking a dynamic range and dividing it up linearly by the number of bits. What am I missing? What would be the differential of amplitude in dB at the lowest levels of signal using 16, 20 or 24 bits?Is this not the reason for the limited low level resolution of the 16 bit format?
The idea that 20 bits would be more than adequate because of the noise of the electronics does not hold water.
HowdyYou said "The idea that 20 bits would be more than adequate because of the noise of the electronics does not hold water." Well, 20 bits is just about as good as can be done right now in hardware. That's a fact. Over time we'll slowly be adding bits but we'll never need more than 24 bits for a ADC or DAC (tho more for processing is a necessity.)
(Ignoring dithered signals) the maximum dynamic range of PCM is the ratio of the loudest representable signal to the smallest, roughly 6dB per bit. I don't know what you mean when you say you were dividing that by bits :)
I'm sorry that I'm not understanding your point.
Thanks for the responses Ted.What I was trying to describe was simply the action of taking the signal and then quantizing it with a grid -- F(s) and the number of amplitude quanitizations possible given the number of bits. With linear quantitization for amplitude there are more gradations for a louder signal. When I was refering to "dividing by the number of bits" I was talking about dividing the signal up by 65,536, not 16.
My apologies for not making my point more clearly and for using confusing language.
Looking at the first few quantizations, I see the second quantization is 2x the voltage of the first, or 6dB, the 3rd is 1.5x the voltage level of the second or 3.5dB higher, the 4th point is 4/3x the voltage of the 3rd or 2.78 dB and so on. The very lowest level signals are crudely recorded in terms of dB differences. The 64,001 gradation is just .0001 dB louder than the 64,000th.
It's surprising what we can hear -- differences in line level amplifiers and cables, even when much grosser distortions exist elsewhere. The low level signal performance of the CD has often been described as inadequate or lacking in comparison to the LP, even when much higher noise levels are present in the LP and LP playback system.
HowdyOne of the differences is that the signal to noise ratio for PCM depends on the current level of the material, on analog media the signal to noise ratio is more or less constant. So as far as signal to noise ratio on quiet material analog wins and on loud material CD wins. Perhaps this is what you were getting to.
I think 20 is about right. 16 would be enough if everyone got the levels right in the reproduction chain - 96db of music on top of 30 db background noise would be enough to cause ear damage. 20 gives you some extra room to make level matching mistakes.Converting 16 bits into analog is pretty tough but it can be done. Anything more is going to be a big waste of money.
Have you ever recorded into 16 bits? Level setting is a real issue.A good mic, mic pre amp and analog console has up to 130dB dynamic range. It will be hard to fit that into 16-bits without doing some peak limiting, or recording at very low levels.
For consumer delivery though, 16-bits plus dithering is fine.
I don't think we disagree. "up to" 130 is a pretty close match to 20 bits.
*** I don't think we disagree. ***Oh, I didn't think we were.
Actually, I've found level setting is still an issue, just not as bad as recording in 16-bit was. Those were the bad old days - I still remember telling someone that the levels should NEVER EVER exceed 0dBFS - he was so used to recording the peaks at +10 (because tape is so much more forgiving). The studio had to junk a lot of early takes because they were clipping like ALL THE TIME!
For example, my current recording ADC gives me about 117dB (actual measured result, as opposed to data sheet specs). Unfortunately, my mic gives +120dB dynamic range, so level setting is not a "set and forget" exercise.
*** applying dither noise isn't necessary when truncating data of 24 bits or more down to 20 bits or more ***Actually, you do (not withstanding that the "24-bit" signal may not have more than 20 bit accuracy anyway).
The best analogy I can think of is taking a 24-bit picture and truncating the colors down to 16-bit. Try and do it with and without dither. Your eyes will prefer the result with dither. Even though the color "noise" in the picture (from the CCD) may be high in the first place (ie. shooting in low light long exposure conditions).
Check out the izotope white paper on dither, which explains this is more detail.
Dither is not necessary if you are not processing the original signal in any way (because they signal has already been dithered by the decimation process in the ADC). However, dithering is required whenever you do any processing on the signal, even if you maintain bit depth. It's because processing can introduce additional quantization noise which needs to be dithered.
"The best analogy I can think of is taking a 24-bit picture and truncating the colors down to 16-bit" CUT!!!!!When it comes to applying dither, truncating to 16 bits is a big difference from truncating to 20 bits. It's a totally different ballgame. Because in the 16-bit case (unlike the 20-bit case), the quantization increment is now bigger than the ambient noise floor, hence applying additional dither noise becomes essential.
"Check out the izotope white paper on dither, which explains this is more detail."
It's an interesting paper, in terms of graphic explanation.
It doesn't really back up the notion that adding noise to truncate 24-bit to 20-bit is necessary.
"Dither is not necessary if you are not processing the original signal in any way (because they signal has already been dithered by the decimation process in the ADC)."
Don't presume it's been dithered. The vast majority of recordings are dither-encoded, but not all recordings.
Besides, in the 24-bit case, if it's then truncated to 20, the 20-bit signal is not the original, but taking that non-original 20 and then truncating it to 16, you definitely need dither in order to minimize the losses from truncation.
"However, dithering is required whenever you do any processing on the signal, even if you maintain bit depth. It's because processing can introduce additional quantization noise which needs to be dithered."
Dither is only required if any resolution or information, which correlates to the original signal or desired processing effects, would otherwise be lost with non-dithered truncation.
*** Because in the 16-bit case (unlike the 20-bit case), the quantization increment is now bigger than the ambient noise floor, hence applying additional dither noise becomes essential. ***Not necessarily. Have you ever shot a picture in high ISO, long exposure? Lots of color noise.
*** Don't presume it's been dithered. ***
If you are using a sigma delta ADC (99% of ADCs these days) the decimation process is inherently self-dithering. That's what I said, which you yourself quoted: "(because they signal has already been dithered by the decimation process in the ADC)".
*** Dither is only required if any resolution or information, which correlates to the original signal or desired processing effects, would otherwise be lost with non-dithered truncation. ***
Post-processing can generate additional quantization noise, which can be audible.
20 bit, 24 bit etc? As an example, Rudy Van Gelder or Verve Mester Editions. Any appreciable difference versus original CD cause the remasters do sound pretty darn good on my Sony XA777ES. TIA!!
The recordings may sound better, but the reason for better sound could be a lot of things. Note that if you used 10 different mastering tools of exactly 20 bits of resolution, you'd likely encounter similar sonic differences amongst them. The 24-bit reasoning becomes a red herring, because those four extra bits are buried in ambient noise, and shouldn't really have any effect. (Maybe the noise itself sounds better, hence is less of an annoyance. And I will not discount that.)
What Todd correctly points out is that if the original signal contains wideband noise, with a suitable distribution, and at a level at or above the target word length's equivalent noise floor, then the signal is self-dithering and truncation to the target length can be done without additional dither.In real-world music productions the total amount of noise originating as thermal noise prior to the ADCs, in the final digital-domain high-resolution master more often than not exceeds the 20bit -120dB noise floor and truncations to word lengths of 20 bit or more don't need dither.
Your 24bit/16bit picture analogy is not quite valid as truncation to 16 bit (i.e. 5/6/5 bits for R/G/B respectively) makes the target noise floor exceed that part of the noise floor in the original image that could have worked as self-dither. In fact, as image sensors offer 60-70dB (10-12bit) of original SNR (10-12bit) in the dark and are shotnoise-limited in the light one can safely say that in almost all applications the original non-correlated image noise lies way below the quantisation noise floor of the 8/8/8 '24' bit format and thus will never serve as self-dither.
If the original raw image does contain visible noise (and trust me, it will ;-), then keep in mind that this high-level noise originates as shot noise or as image processing truncation noise and thus is correlated and non-dithering.
*** What Todd correctly points out is that if the original signal contains wideband noise, with a suitable distribution, and at a level at or above the target word length's equivalent noise floor, then the signal is self-dithering and truncation to the target length can be done without additional dither. ***Typical ambient noise levels captured by the mic is not sufficiently random and also too high to produce self dithering (you can analyze the spectrum to see what I mean). However, the self dithering comes from the decimation process in a sigma delta ADC. In that respect, what Todd originally said is strictly speaking not correct.
As for truncating to the target length, if you do that without dither it will not be as good as using dither, as per my analogy with reducing the color depth of a picture.
Again, ambient noise levels are not necessarily random in either amplitude or spectral content - hence the phenomenon of our ears apparently being able to hear "below the noise floor".
*** Your 24bit/16bit picture analogy is not quite valid as truncation to 16 bit (i.e. 5/6/5 bits for R/G/B respectively) makes the target noise floor exceed that part of the noise floor in the original image that could have worked as self-dither. ***
Try it yourself. Select an image (you can use a noisy image if you like). Using software of your choice, reduce the color depth from 24-bits to 16-bits with and without dither and then compare the results. Your eyes will notice banding if dither is not used.
Hint for generating an image with a lot of color noise - try shooting with a high ISO (which amplifies the CCD signal) in very dark conditions using long exposure. You will find the noise levels to easily exceed 16-bit (5/6/5) resolution. And yet, dithering from 24 to 16 reduces banding. This is independent of the noise level of the original image, as I originally pointed out.
The analogy back to audio is that dithering will reduce the "banding" caused in quantization noise caused by truncation regardless of the noise floor of the original signal.
"Typical ambient noise levels captured by the mic is not sufficiently random"I didn't say 'ambient', I said 'wideband noise, with a suitable distribution'. How about the thermal noise generated in all (equivalent) circuit resistances and capacitances right from your nice tubed large-diaphragm Neumann through the preamps, mixer, ADC front-end and ADC comparators. And this for 24 or more tracks summed. It is wideband, it is near-Gaussian, and it is present in almost all commercial recordings. And it dithers very nicely, thank you. (Try it!)
Have a look at the self-noise of your own minimalist recording setup. Ask yourself why it is not at -144dBFS, even with the microphone replaced with a short and all 60Hz harmonics discarded.
"However, the self dithering comes from the decimation process in a sigma delta ADC. "
My assertions are entirely independent of the architecture of the quantiser.
"Again, ambient noise levels are not necessarily random"
Again, I was not referring to ambient noise.
As for hearing below the noise floor, this is a sad mis-nomer. Yes, our ear can hear below the *noise level* (insofar no maskers are present), but no, we cannot hear below the *noise density floor*.
Try it: take a white noise density floor and then track a 3kHz fade-out into it while keeping an eye on the signal spectrum AND on the summed level (integral of noise density).
You can do this at any level. You'll find you can resolve the sine down to 30dB or so below level, but you'll also find you'll lose it right when hitting the density floor.(However, it would be interesting to try this with stereo noise and the sine panned dead-center. I imagine one can get a couple dBs lower then.)
"reduce the color depth from 24-bits to 16-bits with and without dither and then compare the results. Your eyes will notice banding if dither is not used."
Well, that's what said. Your analogy is wrong because in the case of truncating an image from 8/8/8 to 5/6/5 the target quantisation noise floor is so high that there is no dither-able noise present in the image at that level. Most of the noise visibly present in the source image is correlated and/or of insufficient bandwidth (shot-noise, algorithm quantisation and errors, dark current, and the shot-noise of the dark current ... none of them remotely gaussian). That's why you need to add external dither.
But not necessarily so in audio where we know that the presence of thermal noise at about -120dBFS (or higher) *per track* is a given. Whether a fiinished recording contains enough such noise to be effective as dither for 16 bit output depends on the structure of that recording. But many real, commercial, non-minimalist, recordings seem to qualify for this.
Not that this matters a lot.
*** How about the thermal noise generated in all (equivalent) circuit resistances ***I've already covered this in my other post.
"A good mic, mic pre amp and analog console have dynamic range of around 130dB. A good ADC will have dynamic range slightly exceeding 20 bits.
So, the noise floor of electronics alone are too low to produce self dithering when truncating from 24 to 20."*** Have a look at the self-noise of your own minimalist recording setup. ***
Yes I have. I have two mixers, 4 sets of 24-bit ADCs, a few amps, mics, lots of keyboards (I did my thesis in computer music) so it's hardly "minimalist". I have also used a few studios.
*** Your analogy is wrong because in the case of truncating an image from 8/8/8 to 5/6/5 the target quantisation noise floor is so high that there is no dither-able noise present in the image at that level. ***
The analogy is apt because I am asserting (based on my experience) that there is usually no "dither-able noise" present above 20 bits in audio, therefore there is a benefit to dithering if truncating to 20 bits.
*** Most of the noise visibly present in the source image is correlated and/or of insufficient bandwidth (shot-noise, algorithm quantisation and errors, dark current, and the shot-noise of the dark current ... none of them remotely gaussian). That's why you need to add external dither. ***
Your argument applies equally to audio. That's why it's a good analogy. As I've mentioned in my other post, you can do the measurements and check it out yourself. The "thermal noise" that you speak of is typically not at -120dB, it's much lower than that (at least on my equipment anyway). What's at -120dB are harmonic spikes which is insufficient to cause dithering, and will *benefit* from being smoothed out through dithering. :-)
Put it this way, if the statement was whether there is any benefit in dithering when truncating to 22 bits (instead of 20) - I would say "probably not". But those 2 bits make a big difference, because that's where the "wideband" noise you speak of resides.
"A good mic, mic pre amp and analog console have dynamic range of around 130dB. A good ADC will have dynamic range slightly exceeding 20 bits.
So, the noise floor of electronics alone are too low to produce self dithering when truncating from 24 to 20."Please read back and consider the case that I outlined, where 24 or more tracks have to be mixed to a final stereo master. Or do you deem this not representative for the present state in the music industry? Even when all individual tracks are at around 20b dynamic range, their sum will have a higher noise floor unless massive-scale noise gating is used during mixdown (as in the old days).
There are a handful of ADC chips that resolve near to 120dB of dynamic range (a toddler's hand at that). Far from all convertors in present-day studio gear use these chips. Many use ADCs limited at 17-18b performance.
You seem to be focusing on the best case scenario. It may exist (would you care telling me which ADC you use, or provide me with a spectrum plot of you system's noise floor with shorted input?), but it is not quite typical for the general state of affairs, unless I'm grossly mistaken.
I'm sorry, but you are trying to change the subject.To quote the original statement made by Todd:
"This is also why applying dither noise isn't necessary when truncating data of 24 bits or more down to 20 bits or more. The ambient noise alone would be adequate for such application."
As I've shown, this statement is NOT true (at least not generally). Ambient noise alone is not adequate (and I think we both agree on this).
You seem to be arbitrarily trying to limit the scope of the discussion to specific situations such as poor quality DACs or noisy preamps or mixing a LOT of tracks. Whilst we can argue on and on about specific cases (and whether they represent a "norm" or not), the original statement without qualifications is not factual. Remember, it only takes one counter example to disprove a generalisation.
Even if we wanted to discuss your specific cases, your examples are not valid.
Let's consider your example of mixing 24 or more tracks. You said:
*** Even when all individual tracks are at around 20b dynamic range, their sum will have a higher noise floor unless massive-scale noise gating is used during mixdown (as in the old days). ***
I suspect you don't have a lot of experience mixing. If you mix a lot of tracks, the final mix will exceed 0dBFS unless you attenuate the levels of individual tracks. Therefore the noise floor does not necessarily increase. For example, let's say I have 2 tracks (both with peaks just under 0dBFS). The overall mix will have peaks potentially at +3dBFS unless I attenuate each track by -3dB. Doing so reduces the noise floor of each by -3dB, so the noise floor of the mix is actually at the same level as for the individual tracks.
In fact what typically happens in a mixer is by the time you attenuate the levels of individual tracks, noise levels below 20 bit of the individual tracks are in danger of being "truncated" out of the mix. For example, if we assume noise is at the 20 bit level, attenuating the track level by say -20dB (not atypical for a multi-track mix) causes the noise level to be now at 24 bit level where it is in danger of being truncated out of the final mix altogether (assuming that the mixer operates at internal resolution of 32-bit floating point).
Dithering is advisable to reduce the quantisation noise generated by this truncation, even if the final mix is at 24-bit depth. So mixing actually makes it even more neccesary to apply dithering.
*** Many use ADCs limited at 17-18b performance. ***
No. You are confusing between the measured dynamic range of an ADC and the actual level at which the noise is sufficiently "dense" or "wideband" (your terminology) to act as an effective ditherer. The laws of physics does not change depending on the quality of the ADC. An ADC with a dynamic range of say 102dB (corresponding to your "17 bit" of performance) will have a "thermal noise" envelope far lower than -102dB. Measure it yourself. What you see around -102dB are harmonic spikes that are not sufficient to cause dithering.
"Measure it yourself"I did. Do you think I'm stupid? Do you think I don't know the nature of noise?
Best I ever got was a PCM1804, which after having discarded
any structural noise left me at -108dB rms. Going to evaluate
the new PCM4202 in the coming weeks, I hope.
It was fun for a while, but now I'm signing off, ma'am-your-honour.
*** Best I ever got was a PCM1804, which after having discarded
any structural noise left me at -108dB rms. ***Care to show us a graph of your results?
I checked the data sheet for the PCM1804, and the noise curves on page 11 and 12 (Figures 8-15) clearly show that in PCM mode for single rate and dual rate, the noise levels are close to -140dB apart from a few spikes (which are not ditherable, but these spikes lower the dynamic range to 112dB). In DSD mode, the noise levels are just under -120dB. Even in quad rate mode, the noise levels are around -140dB below 48kHz.
For the PCM4202, the corresponding figures are on page 9-10 of it's data sheet, and show underlying noise to be very similar, just under -140dB. The main difference between the two chips are the lack of harmonic spikes on the PCM4202 (as it's a higher quality ADC), which results in better SNR and THD measurements.
This is consistent with my own measurements of similar ADCs. The laws of physics don't change for different ADCs.
If your results are wildly different, it either means what you are measuring is broken, or there's something screwy with your measurement method.
"I checked the data sheet for the PCM1804, and the noise curves ... clearly show that ... the noise levels are close to -140dB apart from a few spikes (which ... lower the dynamic range to 112dB)"No. The curves show the noise DENSITY, which is, by definition, the specific noise power measured over a unit bandwidth of 1 Hz.
In order to obtain the noise LEVEL (which is what you need for SNR and dynamic range calculations, and which is also what figures in the infamous SNR = 6 x NumberOfBits shortcut), you have to integrate the DENSITY over BANDWIDTH.
For a white noise spectrum with given noise density of Vn (dB) the resulting (RMS) noise level is then Vrms = Vn + 10*log(bandwidth), all in dB.
An ideal 16 bit system with 96 dB SNR over a bandwidth of 22kHz (CD) then has its density at -96-10*log(22000) = -139dBFS.
My PCM1804 with measured 108dB SNR over a bandwidth of 48kHz (running the recorder at 96kHz), has its density at -108-10*log(48000) = -155dBFS.
So if you measure -130dBFS for your system, then the equivalent RMS level (assuming 22kHz BW) is -87dBFS and that's 14.5 bits ;-)
But don't worry, chances are that if you were only looking at FFT-generated plots of the noise density floor your 'measurement' was wrong anyhow, as the plotted level depends on the size of the FFT itself. Try it. Take a white noise signal into Audition and take its spectrum with 1024, 4048, 32000 point FFT ...
The plots in the PCM1804 datasheet are made with 8192 point FFTs. The resulting levels don't show the true per-1-Hz noise density, but rather the density per frequency-bucket of Fsample/8192 Hz. So the floors in the plots are artificially high. That is OK, because to a skilled engineer the 'N=8192' tag in the plot says all.
Included link may help.
- http://lad.linuxaudio.org/events/2004_zkm/slides/saturday/fons_adriaensen-jaaa.pdf (Open in New Window)
... sit down and think about what you've said.What does this say about "noise levels" required for "self-dithering"?
Think about it *really* hard.
PS - I never did say my *system* measured -130dBFS. I said analog circuits can exceed 130dB dynamic range. Not quite the same thing. As for my "measurements" being "wrong", I don't recall giving you any noise level measurements at all. But I'm glad you got really excited.
A good mic, mic pre amp and analog console have dynamic range of around 130dB. A good ADC will have dynamic range slightly exceeding 20 bits.So, the noise floor of electronics alone are too low to produce self dithering when truncating from 24 to 20.
Let's consider the case of "self dithering" caused by ambient background noise during recording. As far as I know, this is a "myth" and I'm not sure many engineers still believe in this. Let me explain why.
Typical peak levels in a live recording: 120dB SPL. Typical ambient noise in a live recording (assuming a concert hall) - around 40-50dB SPL. I have measured far worse, often due to air conditioning.
Typical peak levels in a studio: 100-110dB SPL. Typical ambient noise in a quiet studio: 20-30dB SPL. Again, I have measured studios that are worse (well, mine for instance :-))
These are all numbers based on my experience. Feel free to validate them yourself.
Assuming that we set the levels such that peak is close to 0dBFS, then typical noise level in a recording: around -70-80dB.
You can actually validate this yourself by doing an analysis of commercial recordings. The majority of them will exhibit ambient noise levels at these levels.
These levels are clearly too high to produce a self-dithering effect when truncating from 24 to 20. Particularly when you analyze the spectrum of the ambient noise and realize it is not random.
And in any case you can prove it to yourself. Take a recording with ambient noise at say -70dB. You will find you can easily hear a reverb tail even when it's amplitude is below -70dB.
Even in the best case scenario, noise levels may be at -90-100dB. This may potentially produce a "self dithering" effect for a 16-bit recording, but it won't for a 24-bit recording (with between 20-22 bits effective resolution).
You don't have to believe anything I say, but the numbers kind of speak for themselves, and they are numbers you can easily validate yourself.
"Even in the best case scenario, noise levels may be at -90-100dB. This may potentially produce a "self dithering" effect for a 16-bit recording, but it won't for a 24-bit recording (with between 20-22 bits effective resolution)."I think you meant to swap the numbers: This may potentially produce a "self dithering" effect for a 24-bit recording, but it won't for a 16-bit recording.
Note that nobody is denying that applying dither noise *is* required if a high-resolution audio signal is truncated to 16 bits. But I don't think adding noise is necessary if the same high-resolution signal is truncated to 20 bits.
And comparing dither needs of audio signals with the dither needs of video signals is comparing apples with oranges. Note that video color is not something that is hurt by dynamic range, since the color range is finite. Low rez video color deals with wider spacing between adjacent colors. Which is a lot more benign than such application applied to audio signals.
*** I think you meant to swap the numbers ***No, read it again. The statement is as intended.
*** But I don't think adding noise is necessary if the same high-resolution signal is truncated to 20 bits. ***
It doesn't matter what you think, in reality dithering at 20 bits will make a difference, just like dithering at 16 bits. It may be harder for our ears to hear the difference though.
It's probably a moot point though because I can't think of a valid reason why someone would want to truncate a 24-bit recording to 20-bits. Do you?
*** Note that video color is not something that is hurt by dynamic range, since the color range is finite. ***
I'm not sure what you mean here. Try comparing an image with 8 bit colour vs 16 bit colour vs 24 bit colour and tell me whether it's "hurt" by dynamic range or not.
*** Which is a lot more benign than such application applied to audio signals. ***
Assuming that we set the levels such that peak is close to 0dBFS, then typical noise level in a recording: around -70-80dB.You can actually validate this yourself by doing an analysis of commercial recordings. The majority of them will exhibit ambient noise levels at these levels.
These levels are clearly too high to produce a self-dithering effect when truncating from 24 to 20.
The noise level does not have to be near the quantization noise floor. It only has to be _above_ the quantization noise floor. Dither levels are deliberately set near the quantization noise floor so the dither doesn't reduce S/N too much.
Particularly when you analyze the spectrum of the ambient noise and realize it is not random.It doesn't have to be random. It merely has to be uncorrelated with the musical signal and above the quantization noise floor in level from 0 to fs/2.
*** The noise level does not have to be near the quantization noise floor. It only has to be _above_ the quantization noise floor. ***The point is that there are NO effective dithering sources above 20 bits.
We already know that there is a benefit from dithering when truncating from 24 to 16 bits. Not only is it possible to hear the difference between dithering and non dithering, but it's possible to hear the differences between dithering algorithms (see for example the results of the Great Dither Shootout).
The reason I made a point about background noise typically being at the -70-80dB level is that this is ABOVE the quantisation noise floor of a 16 bit recording. Therefore, if it does not eliminate the benefit of dithering at 16 bits, it also does not eliminate the benefit of dithering at 20 bits.
Otherwise there would be no benefit recording at a resolution higher than about 14 bits.
*** It doesn't have to be random. ***
Note: just because I pointed about that ambient noise is not random, doesn't mean that I am asserting that an effective dithering source has to be random. In any case it is easy to demonstrate that we can hear well below the so called "noise floor" of a room.
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