REW has this possibility:Sorry, didn't catch what you're suggesting.
Then instead of plotting for instance the second harmonic distortion for 1kHz at 1Khz it will plot it at 2Khz the place where you actually hear that harmonic.
REW has this possibility:Sorry, didn't catch what you're suggesting.
You missed my comment that the top graph was obtained at -12 dBFS.THD seems a lot lower up high.
Good question. I don't know for sure, but sometimes it's the only explanation for what I hear. Since the ultrasound region contains (or may contain) interference products of audible frequencies, any perturbations from extraneous signals or noise in this region can reduce the ability of hearing to distinguish or recognize individual quiet sounds.Why, pray tell, would I care of there was an 80dB down distortion product only at, say, 70kHz? That would not make any sense at all to be a "measurement object".
I didn't understand the point of this question. When measuring THD, the energy of the areas corresponding to the harmonic frequencies is summed up without taking into account whether it is tone or just noise.You do understand that it's not only harmonics that are measured, yes? Unless distortions and noise above 20kHz (or maybe 25kHz just to be really, really safe) are powerful enough to cause equipment or drivers to do something nonlinear, what do you believe is the problem.
Do you mean regular single tone fft instead of THD vs frequency plot as I attached above in this post?Then instead of plotting for instance the second harmonic distortion for 1kHz at 1Khz it will plot it at 2Khz the place where you actually hear that harmonic.
You're right, I did miss that, so did it again at about -12db:You missed my comment that the top graph was obtained at -12 dBFS.
Here, an accurate measurement of the CS43131 THD 10 kHz with a notch.
-.5 dBFS
View attachment 456556
-12 dBFS
View attachment 456557
The height of h9 and h7 does not stand a chance for low THD.
As I wrote above, rustle level sounds become indistinguishable from noise. Ideally, transparency is the effect of listening to a live performance, not a recording.As to "loss of transparency" I guess I'll have to ask how you demonstrate that.
It's hard to say why the results are so different. I have no reason to doubt the accuracy of my ADC (Cosmos ADCiso + Cosmos APU). Maybe our DACs are different in some way. I tested it on two dongles with bare cs43131 and cs43198 with almost the same success. It seems @jkim also got similar results with jcally jm20 max.so did it again at about -12db
Oh, there must be a misunderstanding, it's not cs43131 and cs43198 measured in my plot, just the 20 years old AKM chips of a dirt-cheap interface from back then.It's hard to say why the results are so different. I have no reason to doubt the accuracy of my ADC (Cosmos ADCiso + Cosmos APU). Maybe our DACs are different in some way. I tested it on two dongles with bare cs43131 and cs43198 with almost the same success. It seems @jkim also got similar results with jcally jm20 max.
Oh, I see. There is an opinion that these CS chips are also based on very old designs.Oh, there must be a misunderstanding, it's not cs43131 and cs43198 measured in my plot, just the 20 years old AKM chips of a dirt-cheap interface from back then.
The post was about that in this 20 years some DAC chips are still far from perfect as freqs go up.
That's solely from an engineering point of view, it's not about audibility.
Good question. I don't know for sure, but sometimes it's the only explanation for what I hear. Since the ultrasound region contains (or may contain) interference products of audible frequencies, any perturbations from extraneous signals or noise in this region can reduce the ability of hearing to distinguish or recognize individual quiet sounds.
I didn't understand the point of this question. When measuring THD, the energy of the areas corresponding to the harmonic frequencies is summed up without taking into account whether it is tone or just noise.
The IMD test is less clear to me because I haven't had much practice with it and therefore it is difficult to evaluate the result.
Yes, I see the DL200 has a small IMD product at 1kHz. I assume because of the higher THD at 19 and 20 kHz, but find it difficult to correlate it with possible audible effects.
In a few words, I'm trying to measure the difference in sound I'm hearing. I have found differences, but can't draw a line to highlight the more significant ones.
Do you mean regular single tone fft instead of THD vs frequency plot as I attached above in this post?
I mean to do this in this kind of plot:Do you mean regular single tone fft instead of THD vs frequency plot as I attached above in this post?
Ah! Found this option, but it's disabled. I didn't manage to activate it in any way, and couldn't find any information about what it may depend on.It would shift the effects of higher order harmonics further away from the audible band and would be more realistic on audibility.
Of course it matters. But it's been a long time since I've come across equipment of such poor quality that distortion is strongly reflected in the audio band. Even if we look again at the CCIF IMD test of the DL200, where a 1kHz tone occurs. -114 dB is not much considering that the 19 and 20 kHz tones are unrealistically high. I could be wrong, but it's doubtful that this test unambiguously shows a problem that can be heard.You need to look at much more of the error spectrum. Get a plot of the entire error spectrum inside the audio bandwidth. That's what matters.
It is possible to measure THD independently of noise. Ultrasonic noise is not of too much interest, as you wrote and with which I completely agree. That is why I am comparing THD up to 20 kHz over a wide measurement bandwidth. And intermodulation, which leads to tones in the audio range among other things, is also a product of harmonic distortion.Every distortion measurement I know of is THD+Noise. This means that the test signal is removed, and everything else is measured within a given bandwidth. Therefore, noise resulting from image distortion, IMD, etc, all shows up in the measurement, WITHIN THE AUDIO BANDWIDTH, and that's what matters.
It is possible to measure THD independently of noise. Ultrasonic noise is not of too much interest, as you wrote and with which I completely agree. That is why I am comparing THD up to 20 kHz over a wide measurement bandwidth. And intermodulation, which leads to tones in the audio range among other things, is also a product of harmonic distortion.
Of course, the thermal and modulated noise levels have to be controlled too, but in my case I didn't find any problems with that.
By the way, do I understand correctly that you don't think recordings with sampling rates above 44/48 kHz can have better quality or is there a nuances?
Because that is the only thing that can be done with high accuracy. Of course, a single tone is the easiest load for a DUT to handle. But since all distortion other than noise is caused by the same nonlinearities, a THD test will certainly show them all. Even trying to measure TD of a normal multitone doesn't give a stable result, so its accuracy is questionable. I admit that the way complex signals are analyzed can show the presence of some problem, but not its “size”. Also complex signals have a possible problem of harmonics overlapping with signal tones. In the worst case, if you build a signal from a harmonic sequence (1k + 2 + 3 + 4 + ... + 20), the result will be hard to notice harmonic distortion at all, only intermodulation ones. And the “buzz tone” is built exactly on this principle.Why do you WANT to measure only at harmonic frequencies? This makes it literally impossible to calculate a THD for a complex signal with a filled spectrum. Simply removing the original when calculating the SNR, that will tell you what you've got in terms of problems, and why it might or might not be a difficulty. What you need to measure is the effects of nonlinearities, harmonic, IMD, or other. This captures noise, modulated noise, gain drift, thermal aspects, the whole kaboodle. So why not measure what actually matters, not some useless subset of the data?
Thanks for the detailed response! Something to think about.Well, that's more complicated than it ought to be.
The next step is to subtract the input spectrum. The bottom plot looks very, very linear. The top one shows a set of lines at n*500, which is the IMD resulting from the difference in tone frequencies, but compared to some I've seen, it's really not too bad. You did read the info along with the tone, yes? You can analyze it at a length to avoid any need of windowing, yes? It's generated specifically to allow that (continuous across any block length that is an integer number of the initial signal before it's repeated many times).Because that is the only thing that can be done with high accuracy. Of course, a single tone is the easiest load for a DUT to handle. But since all distortion other than noise is caused by the same nonlinearities, a THD test will certainly show them all. Even trying to measure TD of a normal multitone doesn't give a stable result, so its accuracy is questionable. I admit that the way complex signals are analyzed can show the presence of some problem, but not its “size”. Also complex signals have a possible problem of harmonics overlapping with signal tones. In the worst case, if you build a signal from a harmonic sequence (1k + 2 + 3 + 4 + ... + 20), the result will be hard to notice harmonic distortion at all, only intermodulation ones. And the “buzz tone” is built exactly on this principle.
Ok, I don't see any problem to just try “buzz tone”. This spectrum is obtained on DL200 HPA output. It's a quite dirty, but all distortions are below -120 dB. What do you think about it?
View attachment 456816
Next, 9039s
View attachment 456815
This is exactly what is written above. Distortion is as if there is no distortion at all and it is definitely unreal... and beautiful)
Thanks for the detailed response! Something to think about.
Oh, my fault. That's because I didn't see any harmonic distortion in the 9039s output.It is anharmonic
I'm not familiar with matlab, and subtraction in rew gives a visible error. So I just summed all IMDs manually and got -115 dB. Or taking into account the scale shift (DAC to ADC) -109.3 dB. That doesn't seem like much. But it is very disconcerting that the test shows for the 9039s a clean range of almost -160 dB, whereas the same CCIF IMD test gives at best -130 dB.The next step is to subtract the input spectrum. The bottom plot looks very, very linear. The top one shows a set of lines at n*500, which is the IMD resulting from the difference in tone frequencies, but compared to some I've seen, it's really not too bad. You did read the info along with the tone, yes? You can analyze it at a length to avoid any need of windowing, yes? It's generated specifically to allow that (continuous across any block length that is an integer number of the initial signal before it's repeated many times).
Oh, my fault. That's because I didn't see any harmonic distortion in the 9039s output.
I'm not familiar with matlab, and subtraction in rew gives a visible error. So I just summed all IMDs manually and got -115 dB. Or taking into account the scale shift (DAC to ADC) -109.3 dB. That doesn't seem like much. But it is very disconcerting that the test shows for the 9039s a clean range of almost -160 dB, whereas the same CCIF IMD test gives at best -130 dB.
Yes, the DL200 is very good, although it is possible to notice that its sound is not ideal, even on the line output.Still quite decent equipment, there. Instead of looking for harmonics with taht signal, look for multiples of 500Hz. The tones are at prime number frequencies as far as the FFT length, with a stride of 499.xxx Hz apart (fixed number of lines in the fft that is used to create the signal. That means that nonlinarities for interaction between tones all comes at that 499.xx multiple, and the lowest order is 499.xx itself. It's very close to 500Hz, but locked to the FFT value of the stride in the signal generator.
Yes, the DL200 is very good, although it is possible to notice that its sound is not ideal, even on the line output.
Of course, I have seen the spectrum of the original buzz tone and what the DAC adds during conversion. -109.3 dB is the sum of N*500 Hz tones.
I finally found time to continue the tests. And it turned out that last time I tested DL200 I made some mistake, apparently I didn't notice a bad contact. Today's tests show distortion about 20 dB lower.That's still not terrible at all. In what situations do you actually hear distortion? Note that the buzz signal is very close to a pessimal signal. If you change the limits, you can probe the DUT only with the higher frequencies, or only with the lower frequencies, or your choice. That is, if you have matlab handy, or octave, sorry. By changing the range of the individual lines, while keeping the same set of frequencies (just not including all of them) you can find out where the distortion comes from. I wouldn't faint in shock if it was mostly due to higher frequencies.
You still have clear IMD in the distortion spectrum, though. Those peaks at 100, 1500, etc. Interestingly enough 1K is clean, so whatever distortion is very much antisymmetric, I suspect. Still that's low.I finally found time to continue the tests. And it turned out that last time I tested DL200 I made some mistake, apparently I didn't notice a bad contact. Today's tests show distortion about 20 dB lower.
View attachment 457160
As tempting as this idea is, the error levels are too low to even measure due to noise in both the DAC and ADC.