Subharmonics of ultra high frequency information...

[amirm]

Gary, I don't think that is the relevant test. What Frantz is asking is whether our ear is a prefect low pass filter and as such, when the frequency gets high enough, none of the harmonics of a 10 Khz tone is heard. So it no longer matters what its waveform is.

If you stick that in a digital system, it by definition filters everything and the answer becomes what I gave.

FYI, I ran one of those programs yesterday and there is a clear difference between tone shapes but it all sounded wrong to me. The square wave for example, had low frequency overtones. I can't explain why that would be there other than how they are creating them is wrong.

The real test is to have a very high quality analogy generator and listen to the differences.

 

[ack]

Now let's assume that you have a 96 Khz sampling rate but still go to the school that says we do not hear anything above 20 KHz. You can build a DAC with dual filters. The first one can be a special type of filter which does not ring. Such a filter will not have the slope that we need to cut off all the aliasing components (i.e. above the 48 Khz bandwidth of 96 Khz sampling). But since we don't care about preserving all of that extra bandwidth, we can cascade a sharper filter which starts way later than 20 Khz but still manages to cut off everything at 48 Khz. Put another way, this system has a response that is flat to 20 Khz, then gradually rolls off toward zero and at some point, sharply goes to zero (or very close to it).

Amir, how do we know that the steeper filter in the chain won't still ring in the audible range?

 

[amirm]

Amir, how do we know that the steeper filter in the chain won't still ring in the audible range?

Oh, it will ring. It is just that it won't ring nearly as much.

 

[DonH50]

As before, I am hesitant to jump into this, especially since Amir is doing a great job. Nevertheless...

Comments:

1. Filter theory is quite complex and is not my primary area of expertise. I have designed quite a few, analog and digital, and could dig up my grad texts on the subject (spanning several classes) as well as many other reference books. I might be able to put together something that discusses why certain types ring and others do not but it would not be a high priority. Perhaps a few pictures of basic filter responses might be worthwhile(?) Specific questions I would be glad to help answer if I can. As a general rule, steeper filters ring more and have more ripple, so anything (like a higher sampling rate) that allows us to get away with lower-order filters is a Good Thing.

2. Note that aliasing is more an ADC issue than a DAC issue. It's pretty much a given that you can't apply a supra-Nyquist signal to a DAC unless you are doing some funky clocking. On the output side, DACs do generate broadband energy in the form of fast edges, glitches, ringing, etc. We still depend upon the output filtering of the system to control those artifacts.

3. Oversampling DACs (and ADCs), the vast majority in use today, do allow for interpolation in the filter and thus can "add" information that isn't in the original, e.g. "fill in the gaps". There are various types of interpolation schemes and (I am sure) all kinds of discussion about which works best. Note that sampling rate (how fast the DAC clocks) and resolution (how many bits) are independent, at least theoretically.

4. I have a vague memory of taking an old analog audio generator and running the frequency up with different waveshapes. IIRC, beyond a certain point they did all sound the same to me, but as I said earlier I cannot answer Frantz's question with certainty and as of today. My gut says that beyond some person-dependent upper limit everything would sound like a pure sine wave, but I don't know enough about the actual workings of the hearing system to say there is, or is not, a range where different waveshapes matter even though the upper harmonics are rolled off.

5. Fourier proved long, long ago that all waveforms can be reduced to a combination of sinusoids; the catch is how many and how accurately their amplitude and phase weighting must be to recreate the wave you hapen to be observing. It can get very ugly very quickly. As an aside, somewhat related comment, I suspect that I and many others prefer speakers that have very good impulse response because those tend to provide the highest accuracy when driven by complex wideband sources.

Five's a good number on which to cease babbling... - Don

 

[Ethan Winer]

Without vitamins we would die. We could both re-write that statement to make it more palatable and perhaps even true.

I could have elaborated but felt that unnecessary. By "vitamins" I meant as sold by the supplements industry to people who have a normal diet. Versus people in third-world countries. So in that context vitamins are not only unnecessary, but they're potentially dangerous. Not only because vitamins can increase the risk of cancer, but as currently (not) regulated, many supplements contain dangerous levels of heavy metals.

--Ethan

 

[Ethan Winer]

I would like to understand how the peaks and troughs are timed with the sampling frequency. Given perfect clock performance with sampling occurring in perfect intervals what happens when the incoming electrical signal's peak or trough does not fall in the sample window?

That's the whole point of sampling at a rate faster than the highest frequency you want to capture. Once you do that, what happens "between the snapshots" doesn't matter because the input doesn't change fast enough for anything to be lost.

is Nyquist sufficient to capture the combined tones

Yes, of course. This is why digital audio works, and has a frequency response that's very flat within the specified range.

how does the added bit depth of hi-res or even redbook vs compressed affect the gradations of output voltage not just above the actual and not theoretical noisefloor or above the usable additional dynamic range.

That question isn't clear to me, but I can tell you that the number of bits directly affects the level of the noise floor.

We're introducing a new time variable, one that I DO NOT KNOW is considered by the theorem or not

Again, it's already been established that digital audio works and does what it claims. So if anything were "missing" from the theory it would have been discovered long before the CD was invented as a distribution medium.

higher sampling rates increases the probabilities of more accurate data capture of an incoming analog signal which would again theoretically increase resolution particularly in low level information in a mixed signal.

Again, there's no loss of resolution or detail or whatever you want to call it, within the bounds of the sample rate and bit depth used. Low level signals are more related to bit depth than to sample rate.

--Ethan

 

[Ethan Winer]

Then again, when mathematic cannot answer something, then it is open to debate. That get us to "Z & W." If you ask Ethan, he will say there is no Z & W.

Not at all. Rather, I would say (and always do say) that artifacts or losses below the threshold of audibility do not matter and can be safely ignored. We can measure stuff to orders of magnitude lower than anyone could possibly ever hear.

--Ethan

 

[Ethan Winer]

do ALL 10 KHz regardless of wave shape sound the same to us?

Make that 13 KHz to accommodate the few people who can hear to 22 KHz, and then the answer is Yes. However, if you do this test using a typical function generator that outputs the same peak-to-peak voltage for all wave shapes, the volume of the 13 KHz fundamental will change as you switch wave shapes. If you compensate for that, then the answer remains Yes. Last caveat: This also assumes equipment that does not distort audibly at those ultrasonic frequencies, because then you might hear difference frequencies that alias down into the audible range.

--Ethan

 

[RBFC]

I could have elaborated but felt that unnecessary. By "vitamins" I meant as sold by the supplements industry to people who have a normal diet. Versus people in third-world countries. So in that context vitamins are not only unnecessary, but they're potentially dangerous. Not only because vitamins can increase the risk of cancer, but as currently (not) regulated, many supplements contain dangerous levels of heavy metals.

--Ethan

Ethan, as a medical professional of over 30 years, I find the statements above to be misleading. I reviewed several pieces of literature regarding the vitamin/cancer link. In every case I read, the investigators stated that the doses used in the study (MASSIVE overdoses by RDI standards) could be linked to increased risk of cancer. First off, this is not a statement that vitamins CAUSE cancer. There are many factors that can confound a study, making simple inferences such as this impossible. Second, if one is ingesting the recommended amount of vitamin/mineral supplementation, I could find ZERO literature citing risks in that population.

As with any products, there are varying levels of quality. Cheap supplements, containing less-regulated fillers, may contain heavy metals, etc. As this is the What's Best Forum, I don't believe that our membership is interested in poor quality goods of any type. See www.lef.org for vitamins that are produced with the same level of scrutiny as prescription medications, for instance.

Blanket statements regarding areas outside our personal expertise are better left to others, please.

Also, please take any further discussion on the vitamin topic to the Health and Fitness forum, where I have a vitamin thread placed.

Lee

 

[FrantzM]

Ethan

I would beg to differ on the Vitamins supplement issue. "Normal " American diet lacks quite a bit of nutrient so judicious supplementation can lead to better health. Regulation may not be the solution. Education is ... Now back to our thread .
I am under the impression that one can discriminate between tones of equal frequencies but different harmonic content, regardless of the person measured hearing abilities. It does seem that covering the Audio range as well as possible is a good thing to have, making sure that one can recover up to the 6th harmonics of an 8 KHz signal is to me a nice thing to have and can help the ear/brain pulling more information from the signal-induced stimulus...


There is a tendency for many think of digital in term of the imagery of a wave being chopped-off by pulses . We do agree there can't be perfect anything but with digital ... Often such questions arise:

What does happen between samples?
Aren't we losing the information between the samples?

The easiest way to make sense of the Nyquist theorem is for me to forget about the graphical representation of sampled signal.. Rather simply take this as an axiom: If the sampling frequency is twice the highest frequency in the signal, then the signal can be perfectly recovered ... Don't hink of it any other way and remember it is demonstratable and repeatable and has been and is repeated every day you place a phone call and recognize a human voice (which may or may not come from a real human) at the other end .. it iis Nyquist Theorem working and well .. There are problems of implementation, amongst them, we know that some sounds have substantial energy, well above 20 KHz... If we are to sample these signals we remove anything that is highers than half the sampling rate prior to presenting a signal to an ADC ( Analog to Digital Converter). IOW the signal is band-limited so that the the ADC "sees" a signal with the highest frequency components at most half its sampling rate ... For example if the sampling rate is 100 KHz, the original signal bandwidth will be limited to 50 kHz for the conversion to be valid (and Nyquist to hold true) ..


To come back to my hunch that there is something interesting going on with Hi-Rez digital, it would be useful to know :

The highest tones of dissimilar harmonics contents but same frequencies the ear can discern
The threshold of distinction i-e at what level we discriminate?
As well as the highest frequency one can discern.. I have noted in informal tests that the level makes a difference.. I do hear over 16 kHz but do hear much higher or so it seems when I raise the level. I am not sure the ear is a brick-wall filter .. I think 15 KHz at 100 db would likely be perceived by many who would think their hearing limited at 10 KHz ...

Was I OT? I remember the original thread was about sub-harmonics

Happy New Year People !!

 

[Ethan Winer]

this is not a statement that vitamins CAUSE cancer.

Of course, and I was clear to say only that vitamins can increase the risk. The reason is the same nutrient effect feeds cancer cells too. I admit I'm not a medical professional (or even close), but I totally trust my source which is Dean Edell. He reports on all sorts of medical research, and he's mentioned several times that the studies he referred to are exhaustive and conclusive. I believe these are the same studies reported recently by Consumer Reports, who I also trust for advice on topics outside my expertise. They too said that people with normal diets do not benefit from vitamin supplements.

if one is ingesting the recommended amount of vitamin/mineral supplementation, I could find ZERO literature citing risks in that population.

Googling 'vitamins increase cancer' returned almost 15 million hits, including this one:

http://open.salon.com/blog/amytuteurmd/2010/04/01/do_vitamins_increase_the_risk_of_cancer

Cheap supplements, containing less-regulated fillers, may contain heavy metals ... See www.lef.org for vitamins that are produced with the same level of scrutiny as prescription medications, for instance.

I'm not convinced that price is necessarily related to the quality of supplements, just as it's not a conclusive indicator of quality with any product. I recall an article in Consumer Reports that found dangerous levels of heavy metals in quite a few supplement products. That lef.org site sells glucosamine and chondroitin, which immediately negates their credibility to me. Glucosamine and chondroitin was thoroughly discredited in a large double-blind study. I recently had arthroscopic knee surgery and asked my surgeon about that. He told me there's no mechanism by which contents in a pill taken orally could get to a knee joint, which makes perfect sense.

please take any further discussion on the vitamin topic to the Health and Fitness forum, where I have a vitamin thread placed.

I absolutely agree - this is so far off topic it's not even funny.

--Ethan

 

[Ethan Winer]

making sure that one can recover up to the 6th harmonics of an 8 KHz signal is to me a nice thing to have and can help the ear/brain pulling more information from the signal-induced stimulus.

I can't see any value in having a response to 48 KHz, since nobody can hear that high. Certainly analog tape and vinyl LPs can't do that.

What does happen between samples?
Aren't we losing the information between the samples?

I addressed all of that in my post #69 above, and Amir has written quite a bit too. In fact, modern digital audio is perfect, proven by tests where nobody can hear any degradation after one A/D/A generation. One test I read about using a very high-end converter found that nobody could tell the source from the copy even after 10 generations. And that test was done in a pro studio with pro recording engineers as the subjects. So it's clear to me that people who claim they hate the sound of digital - not lossy compression, but PCM and "digital" generally - are not doing their self-testing very carefully.

--Ethan

 

[JackD201]

Even the gentlemen here who implement digital technology for a living don't go that far citing continuing challenges in implementation. As I now understand it, hopefully correctly this time, higher sampling rates aid in said implementation. As in anything however, every solution brings it's own problems so perhaps perfection has not yet been attained.

 

[Phelonious Ponk]

Of course there is a gap between theoretically "perfect" and the inability of pro recording engineers to distinguish between a 10th generation digital copy and the original master, but if it is a moot point. Now we'll await the confident assertion that audiophiles are more experienced listeners than studio engineers...

By the way, I think most (there are certainly exceptions) studio engineers will tell you that the advantage in high res is in recording, where processing consumes bits, and if you start with 16/44.1 you end up with less than Nyquist requires. Its benefit is, well, let's call it "less clear," in the production of distribution media (CDs, digital files).

Tim

 

[microstrip]

By the way, I think most (there are certainly exceptions) studio engineers will tell you that the advantage in high res is in recording, where processing consumes bits, and if you start with 16/44.1 you end up with less than Nyquist requires. Its benefit is, well, let's call it "less clear," in the production of distribution media (CDs, digital files).

Tim

Tim,
Although we find them used in both senses we should not mix bits and hertz as if they are cooking ingredients - are you referring to sampling rate, sample resolution or both?

 

[DonH50]

IME, while higher sampling rates prevail due to other reasons, in the studio more bits are very useful (I would go so far as to say required) to accomodate all the signals when they are summed and thus interact to produce (much) greater dynamic range than any individual source. You need much more headroom in the mixing phase than at the end of the chain (final CD/DVD/whatever). Was true in the analog days and is still true today.

IMO - Don

 

[Phelonious Ponk]

What Don said. And while I've got you, bits is bits . Seriously, I'm just repeating what I've heard and my understanding of it is not complete. That's why I use words like think in my otherwise demonstrative sentences.

Tim

 

[muralman1]

If you page down 5 times, you will come to a nice graph that illistrates what higher resolution can do. NOTE, however, that this shows a 3 mircosecond pulse signal, certainly not something that a microphone would be able to handle. Too bad they did not use an impulse that was more representative of say a 20KHz signal, which has a rise time of about 17 microseconds or so, and yet this pulse is only 3 microseconds WIDE.

I think a picture is worth a thousand words or maybe a thousand questions...ha ha

http://pacoup.com/2008/12/31/playing-the-best-sound-on-ps3-without-hdmi/

Cheers,

Tom

So, it all boils down what the microphone can do, nothing more, nothing less? My system can only handle 16 bits. I tried to imagine hearing thousands of pulses per second, and just can't seem to do it. I am listening to Kronos CD, "Flood Planes." There is so much here. The quartet is playing with percussion, and voices. The musical image is extremely vivid.

 

[Phelonious Ponk]

It sure starts at the mike IMO.

Your humility is admirable, Mike, but I really don't think that's a matter of opinion. Recording starts at the mic.

Tim

 

[JackD201]

Yup.