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Review and Measurements of Okto DAC8 8Ch DAC & Amp

JohnYang1997

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one system can described as linear system + non linearity. And a linear system cna be described using magnitude response and phase response as well as impulse response. The two are fundamentally the same thing just in different form. Unless you can hear over 100khz there is 0 chance of hearing the difference. From 44.1khz playback on the other hand there is very small but audible difference. Other than that it's only possible when digital filter changes the intermodulation distortion the dac produces.
And non linearity is simply all kinds of distortion and noises. And there are harmonic distortion and intermodulation distortion. And no matter what distortion it is, it's included in multitone measurements. And noises is simply measurable. When all of these are under 10ppm. It's simply ridiculous to argue that it's easily audible. It might be tiny bit of difference under most specific condition. But it's simple incredibly small.
And simply there isn't any measurements that isn't done yet. But I do agree some are hard to interpret. However we can surpass the human hearing without knowing the exact threshold of everything.
 

Bliman

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one system can described as linear system + non linearity. And a linear system cna be described using magnitude response and phase response as well as impulse response. The two are fundamentally the same thing just in different form. Unless you can hear over 100khz there is 0 chance of hearing the difference. From 44.1khz playback on the other hand there is very small but audible difference. Other than that it's only possible when digital filter changes the intermodulation distortion the dac produces.
And non linearity is simply all kinds of distortion and noises. And there are harmonic distortion and intermodulation distortion. And no matter what distortion it is, it's included in multitone measurements. And noises is simply measurable. When all of these are under 10ppm. It's simply ridiculous to argue that it's easily audible. It might be tiny bit of difference under most specific condition. But it's simple incredibly small.
And simply there isn't any measurements that isn't done yet. But I do agree some are hard to interpret. However we can surpass the human hearing without knowing the exact threshold of everything.
So if I understand correctly (because you have to treat me like a toddler in this field) there is basically no difference between these dacs in regard to how they sound. And that there aren't any more measurements that could tell us more. So this is basically useless then? Because from the best measurement products here to the worst measurement wise there isn't a difference in sound.
So in your opinion, if you set a good A/B comparison to all the dacs they would all sound the same?
If I am wrong in my assessment please address it in a way that you would explain it to children.
 
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nm4711

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Concerning the short circuit proof:
- Do you know if the Okto dac is protected against these short circuits?
- If the protection exists, is it a protection against permanent shorts or intermittent ones?
The output stage is based on an OPA1632. Looking at TIs datasheet, the short circuit current is lower than the absolute maximum current. So if I interpret it correctly, it should not harm the device.
- Is it certain that everything will measure that well with one output in protection mode?
Because of the high short circuit current the OPs should get warmer. This could lower the performance.
- Do you think that throwing 1000 eur. in a fine piece of gear to purposely put it's outputs in permanent protection mode is intellectually satisfying?
No, this is not sattisfying. I think it is even questionable using a high performing DAC like this with an unbalanced connection.

I use a DAC8 module (not available anymore) for my pair of 3-way active speakers. The Dac is connected directly to my balanced amp. Volume control is done digitally in the DAC chip.
 

JohnYang1997

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So if I understand correctly (because you have to treat me like a toddler in this field) there is basically no difference between these dacs in regard to how they sound. And that there aren't any more measurements that could tell us more. So this is basically useless then? Because from the best measurement products here to the worst measurement wise there isn't a difference in sound.
So in your opinion, if you set a good A/B comparison to all the dacs they would all sound the same?
If I am wrong in my assessment please address it in a way that you would explain it to children.
I wouldn't say complete no difference like many others do in this forum. But I have to say the difference is extremely small. And I doubt there will ever be a difference at sub ppm range. I do hear difference of digital filters. And can have over 70% consistent accuracy doing abx test. But as you can see it's really near inaudible. For most people I doubt they will hear anything under blind test. Different dacs are the same. Eliminate frequency response difference first then do other comparisons. I have many dacs here, and the best performed ones do sound extremely similar and really hard to tell them apart.
 

1234VICE

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Multitone is not any different than music signal.

Thank you for taking the time to educate us. Multitone is still steady state right? At least the data reported is the FFT. How does multitone help us to resolve time-related distortion?

Another test that can be done ultimately is null test. Then you'll just see how linear things can be these days. And how ridiculous this is.

The promise of showing us how rediculous is our thinking is definitely appealing. Does this null test account for time related distortion?

Also if you know a bit about auditory system, we do perform "FFT" in our concha and essentially digitizing the signal(into pulses). There are many more holes here. I don't want to waste too much time.

An FFT transforms a time domain to a fequency domain. Our auditory system projects a time domain to a time-frequency domain. Please consider that I never made the claim that humans hear waveforms.

Do you agree that a transfer function only fully describes a linear system if there are no time-delay operators in the respective differential equation? If not, then indeed this appears to be a waste of time.
 

josh358

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Indeed, if one is to compare gear based on the transfer function alone, one is making the implicit assumption that there are no time-delay operators in the differential equation of the respective devices. Only then, the steady-state response fully describes the behavior of the device in time.

As an example; if one is to adopt the believe that the steady state response fully describes an audio system, this leads logically to the conclusion that all audio systems with the same in-room FR must sound the same. In reality, rooms with different acoustics/speakers sound radically different, even with EQ applied. Moreover, humans do not even prefer flat in-room FR. I am highlighting room acoustics here, for naturally they contain many time-delay operators (reflections).

The underlying mechanism here is that humans obviously do not perform FFT, and our hearing features a time dimension. Then, to fully characterize a system by measurements, this would require to fully resolve its governing differential equations as far as I am concerned. Restricting oneself to the transfer function might not be justified. Another challenge indeed is to connect the differential equations (measurement) to psychoacoustics.

I do not know to what extend feedback (time delay) can generate audible distortion in a DAC, but it is a valid and interesting question. Naturally, room acoustics are much more extreme.

I feel some members in this thread reject any discussion beyond the published measurements. However, you are proposing a scientific method to test the suggested audibility of feedback (abx), and in my opinion, any scientific attempt to improve our knowledge on psychoacoustics should be applauded, rather than be disregarded as unscientific. Your hypothesis could be wrong of course, and we should treat subjective experience with extreme skepticism, but I value your two cents.
Agreed, and thank you.

I've now seen several DAC makers and a chip designer point to the importance of time domain behavior, but I haven't seen any studies of its audibility as it pertains to DAC's. I'd be most interested if someone is aware of any salient research (or from a designer, in-house experience).
 

JohnYang1997

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Thank you for taking the time to educate us. Multitone is still steady state right? At least the data reported is the FFT. How does multitone help us to resolve time-related distortion?



The promise of showing us how rediculous is our thinking is definitely appealing. Does this null test account for time related distortion?



An FFT transforms a time domain to a fequency domain. Our auditory system projects a time domain to a time-frequency domain. Please consider that I never made the claim that humans hear waveforms.

Do you agree that a transfer function only fully describes a linear system if there are no time-delay operators in the respective differential equation? If not, then indeed this appears to be a waste of time.
What is steady state, you have to ask yourself. How a complicated alternating signal has anything to do with "steady state". None dacs can predict such signal. So thinking it's steady state is not accurate.

In terms of time domain. Phase response plus magnitude response can describe just that(square wave sure works too). If you are thinking about time shift. If it's shift by the same time hence delay then it's nothing wrong with it. If the dac shift something depending on time or signal then you will see frequency shift. That's jitter. (other wise you may hear pitch constantly shift down or up) In fft you will see a thicker band rather than precise discrete frequency. But in fft it's also depending on window function. That's that. In general jitter is not a problem for normal frequencies. We test jitter at 1/4 of sampling rate which is also tested.

And null test includes everything that's different from the original. Of course inclues time errors. It's just not separated from other distortion or noise. However it's everything that's different. It's only normally visible at 1000x amplification. We didn't really forget everything here. This way we don't get much information of why it measures that way, just a result. We prefer measure individual tests that can reveal more separated information.

Sure you can use square wave, and it's convenient to identify digital filter this way. But it's generally no difference in sound unless things go horribly wrong.
 

JohnYang1997

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Agreed, and thank you.

I've now seen several DAC makers and a chip designer point to the importance of time domain behavior, but I haven't seen any studies of its audibility as it pertains to DAC's. I'd be most interested if someone is aware of any salient research (or from a designer, in-house experience).
Do your blind tests of digital filter and post abx results here. Otherwise no one is going to believe you. I have done the blind test myself and only be able to have 70% accuracy and it's probably the change in imd content. Also if you ask manufacturers of course they will tell you it's audible otherwise who is going to buy their chips.
 

Bliman

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I wouldn't say complete no difference like many others do in this forum. But I have to say the difference is extremely small. And I doubt there will ever be a difference at sub ppm range. I do hear difference of digital filters. And can have over 70% consistent accuracy doing abx test. But as you can see it's really near inaudible. For most people I doubt they will hear anything under blind test. Different dacs are the same. Eliminate frequency response difference first then do other comparisons. I have many dacs here, and the best performed ones do sound extremely similar and really hard to tell them apart.
Ok thank you for the response.
 

josh358

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I wouldn't say complete no difference like many others do in this forum. But I have to say the difference is extremely small. And I doubt there will ever be a difference at sub ppm range. I do hear difference of digital filters. And can have over 70% consistent accuracy doing abx test. But as you can see it's really near inaudible. For most people I doubt they will hear anything under blind test. Different dacs are the same. Eliminate frequency response difference first then do other comparisons. I have many dacs here, and the best performed ones do sound extremely similar and really hard to tell them apart.
The amusing thing is that after trashing me, your empirical observations are very similar to mine. It's hard to believe that most of the audible differences are due to frequency response, though, considering how most DAC's measure. And that suggests time domain issues. Why else for example would a linear phase reconstruction filter sound different from a minimum phase reconstruction filter when there's virtually no difference in the steady state measurements?

1564336178264.png

I hear more of a difference between the linear and minimum phase filters than I do between the fast and slow filters.
 

JohnYang1997

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The amusing thing is that after trashing me, your empirical observations are very similar to mine. It's hard to believe that most of the audible differences are due to frequency response, though, considering how most DAC's measure. And that suggests time domain issues. Why else for example would a linear phase reconstruction filter sound different from a minimum phase reconstruction filter when there's virtually no difference in the steady state measurements?

View attachment 30224
I hear more of a difference between the linear and minimum phase filters than I do between the fast and slow filters.
For low sampling rate, of course it changes phase response and can affect the sound. It's proven to be audible in studies. I saw one in this forum. I was talking about the post of ess that runs at 384khz.
My blind test was run at 96khz to prevent phase or frequency response difference. It's very likely to be the imd different filters generated. I have a thread a few months ago.
And take a step back, even at 44.1khz the difference between digital filters are very small. Saying it makes all the difference is also inaccurate and wrong.
And how do you say it's no difference in "steady state" measurements? There are imd that changes with them.
 

josh358

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Do your blind tests of digital filter and post abx results here. Otherwise no one is going to believe you. I have done the blind test myself and only be able to have 70% accuracy and it's probably the change in imd content. Also if you ask manufacturers of course they will tell you it's audible otherwise who is going to buy their chips.
You know, I don't much care if anyone believes me. I posted my impressions because I hoped they would be of interest to others interested in this DAC. But as I said, the demo unit is available for anyone who wants to try it themselves, and even if everything I said was accurate, I can't say which DAC people would prefer in their own systems.

I'd note though that you've heard differences, and I don't doubt you, in part because your impressions are similar to mine and those of many, many others. As I'm sure you know, it is very hard to ABX a subtle difference on a changing audio signal and I'm not sure I could do it on the subtler differences I heard, unless perhaps with a carefully selected short loop. I do believe that I can ABX the perceived difference in tonality, again, on a selected loop of violins or soprano, and as I said, hope to try it.

IMD could certainly be part of the reason these DAC's sound different, and while the IMD in the Okto is only 10 dB lower than the Schiit and so shouldn't sound dramatically different, it could explain why the Okto sounded cleaner to me on some material (but not why the Schiit sounded cleaner on orchestral climaxes and massed strings -- though that could potentially because the subjective HF emphasis is exaggerating HF distortion in the recording).

As to the DAC manufacturers, yes, they're selling a product but that doesn't explain why they make time domain response a factor in their design efforts, or why they'll mention these things to you in a friendly personal conversation.
 

JohnYang1997

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You know, I don't much care if anyone believes me. I posted my impressions because I hoped they would be of interest to others interested in this DAC. But as I said, the demo unit is available for anyone who wants to try it themselves, and even if everything I said was accurate, I can't say which DAC people would prefer in their own systems.

I'd note though that you've heard differences, and I don't doubt you, in part because your impressions are similar to mine and those of many, many others. As I'm sure you know, it is very hard to ABX a subtle difference on a changing audio signal and I'm not sure I could do it on the subtler differences I heard, unless perhaps with a carefully selected short loop. I do believe that I can ABX the perceived difference in tonality, again, on a selected loop of violins or soprano, and as I said, hope to try it.

IMD could certainly be part of the reason these DAC's sound different, and while the IMD in the Okto is only 10 dB lower than the Schiit and so shouldn't sound dramatically different, it could explain why the Okto sounded cleaner to me on some material (but not why the Schiit sounded cleaner on orchestral climaxes and massed strings -- though that could potentially because the subjective HF emphasis is exaggerating HF distortion in the recording).

As to the DAC manufacturers, yes, they're selling a product but that doesn't explain why they make time domain response a factor in their design efforts, or why they'll mention these things to you in a friendly personal conversation.
None of what I said should apply to schiit. There are countless design flaws in many of their products. It's very possible to hear any sort of difference. Many of them are essentially broken in my book.
Simply you can try to record it via a good adc and replay through a genuinely good dac. I have done things like this, and it proves that better measurement is better measurement. Better measured equipment can basically reproduce worse equipment.
 

josh358

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For low sampling rate, of course it changes phase response and can affect the sound. It's proven to be audible in studies. I saw one in this forum. I was talking about the post of ess that runs at 384khz.
My blind test was run at 96khz to prevent phase or frequency response difference. It's very likely to be the imd different filters generated. I have a thread a few months ago.
And take a step back, even at 44.1khz the difference between digital filters are very small. Saying it makes all the difference is also inaccurate and wrong.
And how do you say it's no difference in "steady state" measurements? There are imd that changes with them.
Sure. I did most of my listening at 44.1 kHz because it is more demanding of the DAC. Interesting about the IMD results, though unless I'm missing something that doesn't rule out time domain issues at 44.1 kHz.

I'm not sure what you mean by saying it makes all the difference. Are you talking about time domain response? Nothing I've said here about that is anything but speculation -- it is an obvious subjective difference (unlike most of the others) and I don't think something like IM distortion would explain the difference between subjective frequency response. Certainly the guy from Emotiva made a similar speculation, but even he was guessing at the correlation.

I was comparing linear phase fast to minimum phase fast and linear phase slow to minimum phase slow. The steady state measurements on those pairs look quite similar to me, whereas they differ significantly between the fast and slow measurements.
 

Bliman

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None of what I said should apply to schiit. There are countless design flaws in many of their products. It's very possible to hear any sort of difference. Many of them are essentially broken in my book.
Simply you can try to record it via a good adc and replay through a genuinely good dac. I have done things like this, and it proves that better measurement is better measurement. Better measured equipment can basically reproduce worse equipment.
But you just said you can hear no difference between dacs. Only a minimal amount.
 

JohnYang1997

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Sure. I did most of my listening at 44.1 kHz because it is more demanding of the DAC. Interesting about the IMD results, though unless I'm missing something that doesn't rule out time domain issues at 44.1 kHz.

I'm not sure what you mean by saying it makes all the difference. Are you talking about time domain response? Nothing I've said here about that is anything but speculation -- it is an obvious subjective difference (unlike most of the others) and I don't think something like IM distortion would explain the difference between subjective frequency response. Certainly the guy from Emotiva made a similar speculation, but even he was guessing at the correlation.

I was comparing linear phase fast to minimum phase fast and linear phase slow to minimum phase slow. The steady state measurements on those pairs look quite similar to me, whereas they differ significantly between the fast and slow measurements.
Frequency response, supply noise, harmonic and im distortion. All of them. You have to isolate each one to possibly identify the audibility. And you don't want to cross interpret measurements. Even two DACs use same dac chip, they need to be measured separately. Let alone different chip or even different topology. My dx3pro showed different imd pattern in measurements.
And you shouldn't say time domain issue, but phase response. In time domain it's hard to relate to our hearing range. Simple low pass filter will have phase response changed at half of the frequency of magnitude response -3db point. It's technically possible to be different. But I don't think it's the main issue of schiit. There are many more issue with schiit products.
 

JohnYang1997

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But you just said you can hear no difference between dacs. Only a minimal amount.
Well-engineerd ones. Not horrible ones. Well I should've said most dac in that post. I just realized you said worst measurements.
 

josh358

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None of what I said should apply to schiit. There are countless design flaws in many of their products. It's very possible to hear any sort of difference. Many of them are essentially broken in my book.
Simply you can try to record it via a good adc and replay through a genuinely good dac. I have done things like this, and it proves that better measurement is better measurement. Better measured equipment can basically reproduce worse equipment.
If I can't do the blind test, I think I'll try your technique -- the Lynx has decent ADC's.

Personally, though, I'd want to digitize an analog input and A/B it with the output of the DAC. That seems to me the acid test and in my experience (admittedly, years ago when DAC's were less refined) some DAC's do very well while others fail. Unfortunately, I no longer have a good analog source so I'd invite anyone who can do it to give it a try -- I'd be interested in knowing which is more accurate, and in which areas.
 
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