George, the spdif waveform shots I took were just incidental- that's not my primary focus and I'm sorry I even mentioned looking at those since it dragged things completely away from the central point of my measurements- what is the analog output signal? What happens inside the digital black box is intellectually interesting, but it's what comes out that makes the music.
You're kidding right?
The FFT that SY posted shows no inharmonic distortion all way down into the dirt. Just how capable do you want? I'm at a loss. Count me out - I don't see the point. If a DAC and the USB to spdif interfaces are designed half way decently, then there isn't' any trace of the jitter in the analog signal. Isn't that the signal that really counts? Putting a bandage on a bad spdif receiver/DAC seem silly to me. Why not just use a good one?
http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/C41%20SPDIF%20interface%20flawed.pdf
The Essex server seems to be dog-slow at the moment, however this mirror worked fine for me:
http://www.scalatech.co.uk/papers/aes93.pdf
Found the article on this test signal. Seems it is used to show effect jitter has on a DAC. Which differs from one DAC to the other (more the receiver in the DAC, not the DAC chip itself i guess). Some DACs were measured, with the results in the paper.
Do we just want to use this signal only to verify that the DAC is affected by jitter and that it can be measured??
I would shure say this is a pre-requisit.
Need to study the paper a lot better.
If someone could mail me the testsignals (assume they are wav) i would be happy. Could become handy some day, allthough i don't have audio cards or the fancy equipment mentioned in the pdf.
Mmm, edited as i could already shoot holes in my reasoning.
Do we just want to use this signal only to verify that the DAC is affected by jitter and that it can be measured??
I would shure say this is a pre-requisit.
Need to study the paper a lot better.
If someone could mail me the testsignals (assume they are wav) i would be happy. Could become handy some day, allthough i don't have audio cards or the fancy equipment mentioned in the pdf.
Mmm, edited as i could already shoot holes in my reasoning.
Last edited:
You're kidding right?
Think what is meant is that SY should show an FFT with the signal with excessive jitter. There should be distortion as posted by the others then as no dac in the world would be able to totally get rid of it. This to prove the measurement setup is o.k.
SY has the opportunity to listen to the HIface & report back but I don't believe he will allow himself to do so!You're kidding right?
I challenge you, Pano to listen to the modified Hiface & tell me it sounds the same as the Chinese USB -SPDIF, indeed any SPDIF you care to put it up against. All you have to do is listen. I will pay for the postage to & postage from your place! You can listen to the attenuators also. If you then want to measure them, fine!
If you're not interested, any other takers?
Exactly! This would seem to me to be the first step in any experiment, no?
Depends what you want to show. Which i think was made clear in the posts from all sides. Fine with me.
I haven't done that yet. You've indicated strongly that you are not happy that the results so far don't show any actual advantage to the box that you're selling; rather than deal with the technical realities, you have resorted to questioning my objectivity and competence (and I must say that your grasp of basic technical issues does not appear to be profound), shifting the target repeatedly, pulling me off on side issues, and badgering me about completing several weekends of work (for which I'm not charging you) overnight.
At this point, I'm not inclined to donate any more labor to your business.
Hello
Did you see my question at this post ?
http://www.diyaudio.com/forums/digi...tenuators-jitter-reducers-59.html#post2357577
Thank
Bye
Gaetan
Excellent point pano. Trouble is everyone's sure theirs is good
Post-purchase rationalisation I say.
Yes, I saw it but don't understand it. The signal I showed is an audio file with jitter built in. It's not mine, it's from the Stereophile test CD #2 - track 26.
More info here: http://www.stereophile.com/features/338/index11.html
I just wanted to show that jitter can be seen in the file and in a recording of that file. If the tones and jitter are different, they will look different in FFT. But you'll see them. I don't have any other jitter signals.
Is that what you were asking?
Hello
A use a jitter test using wav file with a signals of 11025Hz + 229.6875Hz, I was just currious to know if you know this test.
Thank
Bye
Gaetan
Yes, you are correct, I have been ungracious - I accept your measurements as you have presented them & thank you for the effort you have put in. I admit that the presented results show no difference between the $30 USB-SPDIF device & my €275 HIface USB-SPDIF device. So, based on these measurements there should be no sonic difference between the devices.
The results presented for the attenuators don't show the stated jitter effects that I had predicted either.
I ask you finally to have a listen to the $30 Vs €275 device & report back your impressions. You can do the same with the attenuators, if you wish. Nothing scientific, DBT or anything, just a listen.
I apologise for my robust attitude but I know that the Hiface sounds substantially & unmistakeably different to the stock version & I'm assuming that the $30 is not better sounding than the stock Hiface. I can only conclude that your measurements don't reveal the heard differences.
Hi John - I suspect SY is on a hiding to nothing here in terms of the listening test. I'd hasten to add that the hiding is probably not from you!
Its the old double bind dilemma - he KNOWS which device is which. Moreover his predilection following the measurements he has made is (I presume) to consider the outputs reasonably close if not identical in all practical sense.
As we all know, this will flavour the listening test regardless of any attempt at impartiality. It may even contribute to an exaggerated bias TOWARD the HIface as a subconscious response to a conscious knowledge of personal bias!
So, if he listens and returns a verdict of "no discernible difference" or "preference fort the cheap USB" he's clearly bias against the HIface device. Alternatively, if he finds for the HIface, its because he has attributed to it a degree of sophistication (the 192 capability) and knows its the more expensive. Or a positive bias as described above.
Its fraught, especially after a journey like this.
Which isn't advice to SY not to listen or respond - just a caution regarding interpretation of any views he may come back with.
Its the old double bind dilemma - he KNOWS which device is which. Moreover his predilection following the measurements he has made is (I presume) to consider the outputs reasonably close if not identical in all practical sense.
As we all know, this will flavour the listening test regardless of any attempt at impartiality. It may even contribute to an exaggerated bias TOWARD the HIface as a subconscious response to a conscious knowledge of personal bias!
So, if he listens and returns a verdict of "no discernible difference" or "preference fort the cheap USB" he's clearly bias against the HIface device. Alternatively, if he finds for the HIface, its because he has attributed to it a degree of sophistication (the 192 capability) and knows its the more expensive. Or a positive bias as described above.
Its fraught, especially after a journey like this.
Which isn't advice to SY not to listen or respond - just a caution regarding interpretation of any views he may come back with.
Hi,
First, it is the 1616M, not the 1212M, second, no.
If you know how to modify digital gear for lower noise on the powersupplies (that is basically it) it should not be difficult anyway.
Ciao T
First, it is the 1616M, not the 1212M, second, no.
If you know how to modify digital gear for lower noise on the powersupplies (that is basically it) it should not be difficult anyway.
Ciao T
Hi,
I'd expect to see an FFT noisefloor of around -143dBFS for a 16 Bit Signal with 64K FFT bins.
Care to explain why we see something that around 20dB worse than what is needed to not degrade 16 Bit Audio Signals with equipment that is, how did you say, "impeccable"?
I would suggest again to all those reading the thread, compare the measurements taken by JA in stereophile, I believe he uses 16K FFT bins on the AP2, which would produce a FFT noisefloor at -137dBFS and which can be seen quite closely matching the theoretical limits in the FFT Plots here:
Stereophile: Lindemann & Stello USB-S/PDIF converters
And what's the deal with that huge (for a competently designed solid state device) HD?
It should be noted that no-one considers the Musical Fidelity X-24K DAC used in these tests at stereophile is not generally considered impeccable (actually, I consider it a bit a p.o.s. and it's over 10 Years old), it uses a PCM1716 DAC, which has a much worse objective performance than the Chip's Behringer uses in the DCX. Yet it shows much lower noise and distortion than this supposedly "impeccable" setup.
In fact, if a J-Test had been performed and not a simple HD measurement the majority of the jitter sidebands shown in JA's measurements in stereophile would have been hidden below the noisefloor.
More-so, given the "cheap chinese USB converter" uses a device from the PCM290X which produces huge amounts of jitter (which is well documented) that even the CS8420 ASRC (whose ability to suppress jitter is also well documented) cannot properly clean up it begs the question where this jitter has disappeared to in these measurements, because it should be visible even with this poor noisefloor and just an HD test.
I had expected the measured result to be bad, knowing what do about the "test" gear involved, but there is no reason it should be as appalling as what is shown and I feel it demands an explanation. Just looking at the posted result I cannot but feel "it smells very fishy".
Ciao T
My laptop with either the Chinese USB->spdif straight in or the modified Hiface USB->spdif with both attenuators, run into DCX2496 digital input. DCX analog output run to M-Audio PCI card in my lab computer for FFT. No jitter sidebands seen from any of the sources. 64k data points, 96k sample rate.
I'd expect to see an FFT noisefloor of around -143dBFS for a 16 Bit Signal with 64K FFT bins.
Care to explain why we see something that around 20dB worse than what is needed to not degrade 16 Bit Audio Signals with equipment that is, how did you say, "impeccable"?
I would suggest again to all those reading the thread, compare the measurements taken by JA in stereophile, I believe he uses 16K FFT bins on the AP2, which would produce a FFT noisefloor at -137dBFS and which can be seen quite closely matching the theoretical limits in the FFT Plots here:
Stereophile: Lindemann & Stello USB-S/PDIF converters
And what's the deal with that huge (for a competently designed solid state device) HD?
It should be noted that no-one considers the Musical Fidelity X-24K DAC used in these tests at stereophile is not generally considered impeccable (actually, I consider it a bit a p.o.s. and it's over 10 Years old), it uses a PCM1716 DAC, which has a much worse objective performance than the Chip's Behringer uses in the DCX. Yet it shows much lower noise and distortion than this supposedly "impeccable" setup.
In fact, if a J-Test had been performed and not a simple HD measurement the majority of the jitter sidebands shown in JA's measurements in stereophile would have been hidden below the noisefloor.
More-so, given the "cheap chinese USB converter" uses a device from the PCM290X which produces huge amounts of jitter (which is well documented) that even the CS8420 ASRC (whose ability to suppress jitter is also well documented) cannot properly clean up it begs the question where this jitter has disappeared to in these measurements, because it should be visible even with this poor noisefloor and just an HD test.
I had expected the measured result to be bad, knowing what do about the "test" gear involved, but there is no reason it should be as appalling as what is shown and I feel it demands an explanation. Just looking at the posted result I cannot but feel "it smells very fishy".
Ciao T
You would, why? I've never gotten that with a home brew 16 bit measurement. More like -130dB real world. And I tend to use 32K bins just for speed anyway. Of course I don't own multi-kilodollar AP gear, either. And I see about 5-6dB difference in noise floor from a DCX with active and passive outputs.
Do you think that jitter would not show up with a -120dB noise floor?
Do you mean harmonic distortion? Is it that bad? H5, H7, H9 are higher than they should be, but it's a cheap 3 opamp circuit with an electrolytic coupling cap. Part of that "Behringer sound."
So are you saying the DCX suppress jitter? Isn't that a good thing? Not for this test, of course - but if you mean that the DCX in not valid for a jitter test because it suppresses it, why not say so? That would be very important to the test.
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