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Is DAC ultrasonic/RF output important?

rabski

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I get that Nick, but I was responding to an earlier post of the usual 'it is too low to matter' variety.

That said, whilst it may cause issues in the analogue stages of a DAC, if the DAC outputs it, it will certainly be a potential issue in extremely wide-band amplifiers. I have never understood the benefit of 'wide open' FR response outside the audio range, as it seems to me an excellent way to cause all manner of problems.
 
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Fourlegs

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I get that Nick, but I was responding to an earlier post of the usual 'it is too low to matter' variety.

That said, whilst it may cause issues in the analogue stages of a DAC, if the DAC outputs it, it will certainly be a potential issue in extremely wide-band amplifiers. I have never understood the benefit of 'wide open' FR response outside the audio range, as it seems to me an excellent way to cause all manner of problems.
I have never heard of the issue being that the dac passes through the noise but rather that the noise gets converted to audible imd within the dac analogue stages. I stand to be corrected though.
 

Shadders

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the general acceptance is that the HF noise (aka RF noise) causes IMD in the sensitive analogue stages of DACs as opposed to in following less sensitive devices such as amplifiers. Indeed the same RF noise/IMD artifacts can be heard in DACs direct driving headphones.
Hi,
This is just not correct. The number of tests completed on DAC's are quite vast, from many sources, and there may be the odd one where there is an issue in the output, whch may be IMD related, but i certainly have not seen it (sources, Hifi News, Stereophile, ASR).

All issues i have seen in a DAC using the standard THD test are harmonically related.

Regards,
Shadders.
 

Fourlegs

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Hi,
This is just not correct. The number of tests completed on DAC's are quite vast, from many sources, and there may be the odd one where there is an issue in the output, whch may be IMD related, but i certainly have not seen it (sources, Hifi News, Stereophile, ASR).

All issues i have seen in a DAC using the standard THD test are harmonically related.

Regards,
Shadders.
I’m glad we have an expert walking amongst us. I must introduce him to Rob Watts who will no doubt be glad of the more experienced viewpoint of our very own irreplaceable Shadders.
 
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rabski

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I have never heard of the issue being that the dac passes through the noise but rather that the noise gets converted to audible imd within the dac analogue stages. I stand to be corrected though.
I imagine both are possible.

Frankly, I've long given up on the 'it just cannot happen' approach. Far too often I've found that in practice, no matter what the figures and theory suggests, when it comes to actually nailing things together, some very odd things can occur.
 
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Shadders

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I’m glad we have an expert walking amongst us. I must introduce him to Rob Watts who will no doubt be glad of the more experienced viewpoint of our very own irreplaceable Shadders.
Hi,
You are now deflecting by appealing to authority.

Do you know what modulation Watts DAC's use ?

Do you know what DAC architecture Cirrus Logic, Analog Devices, Texas Instruments and AKM use ?

Regards,
Shadders
 

tuga

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Hi,
This is just not correct. The number of tests completed on DAC's are quite vast, from many sources, and there may be the odd one where there is an issue in the output, whch may be IMD related, but i certainly have not seen it (sources, Hifi News, Stereophile, ASR).

All issues i have seen in a DAC using the standard THD test are harmonically related.

Regards,
Shadders.

You could read the topic I mentioned instead of assuming.
RME's Matthias Carstens think it may be a possibility.
 

Shadders

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You could read the topic I mentioned instead of assuming.
RME's Matthias Carstens think it may be a possibility.
Hi,
I did read the topic. I was responding to fourlegs, NOT your italicised text, which is different to fourlegs statements.
Regards,
Shadders.
 
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tuga

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I imagine both are possible.

Frankly, I've long given up on the 'it just cannot happen' approach. Far too often I've found that in practice, no matter what the figures and theory suggests, when it comes to actually nailing things together, some very odd things can occur.

Apparently in this case the issue is measurable, it just wasn’t showing because many measurements are focusing only in the audio band or what is audible.
 

Fourlegs

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I imagine both are possible.

Frankly, I've long given up on the 'it just cannot happen' approach. Far too often I've found that in practice, no matter what the figures and theory suggests, when it comes to actually nailing things together, some very odd things can occur.
RW has posted many times elsewhere but this is a typical explanation from him.

”The actual distortion mechanism is noise floor modulation - random RF noise gets into the analogue electronics, and at RF frequency things are very non-linear. Then you get intermodulation distortion with the audio signal and the random RF noise, giving you random intermodulation products that is in the audio bandwidth. So noise pumps up and down with the audio signal, making it sound harder and brighter. Unfortunately, the brain is very sensitive to this effect.”
 
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andrew s

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RW has posted many times elsewhere but this is a typical explanation from him.

”The actual distortion mechanism is noise floor modulation - random RF noise gets into the analogue electronics, and at RF frequency things are very non-linear. Then you get intermodulation distortion with the audio signal and the random RF noise, giving you random intermodulation products that is in the audio bandwidth. So noise pumps up and down with the audio signal, making it sound harder and brighter. Unfortunately, the brain is very sensitive to this effect.”
From my research into this some time back. This view is based on his listening and hearing differences in different implementations of his devices. The effects are below measurable levels so his association of cause and effect is based on his simulations of the devices.

I am in no position to comment on the veracity of these claims without seeing the details of the simulations and if they include all the necessary physics (thermal noise etc.) but understandably they are not freely available.

At one time I simulated complex systems for a living. The history of simulation show how hard it can be to include all the necessary details. Climate models that refused to be stable and super nova that refused to explode.

Regards Andrew
 

tuga

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From my research into this some time back. This view is based on his listening and hearing differences in different implementations of his devices. The effects are below measurable levels so his association of cause and effect is based on his simulations of the devices.

I am in no position to comment on the veracity of these claims without seeing the details of the simulations and if they include all the necessary physics (thermal noise etc.) but understandably they are not freely available. At one time I simulated complex systems for a living. The history of simulation show how hard it can be to include all the necessary details

Regards Andrew
A link to a discussion you might be interested in reading here.
 
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rabski

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At one time I simulated complex systems for a living. The history of simulation show how hard it can be to include all the necessary details. Climate models that refused to be stable and super nova that refused to explode.
Similar things apply to audio circuits at any level.

You can model endlessly in Spice, PSU designer, etc. but when you get it on the bench, all manner of surprises await. No matter how much you've accounted for every possible thing, there is always something else. Even once you've got it 'clean' in the workshop and every sensible measurement looks spot on, put it in a working system and be prepared for it to potentially sound like a dog's dinner.

Such is life...
 

Fourlegs

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A link to a discussion you might be interested in reading here.
Thanks for that link and the link within the link. It is amusing in the Bits Is Bits? thread to read the same old non acceptance of the noise issues on digital transmission and with digital to analogue conversion despite Jussi‘s helpful and patient explaining.
 
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TheFlash

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To answer direct the question in the title

Is DAC ultrasonic/RF output important?​

It may well be in some systems (the wide FR amps mentioned by the honourable @rabski for example), but I believe that the impact of ultrasonic/RF noise on the DAC itself is far more likely to impact sound quality. This RF can either reach the DAC from outside or be generated by components inside the DAC case itself, same impact.

For those of us who don’t design our own DACs, all we can do to minimise the external noise, to stop it reaching the DAC from outside.

Those who do design their own DACs may be able not only to minimise the impact of incoming RF but also minimise the impact of RF generated inside the case through component selection, layout, shielding and EMI/RFI absorbent material.
 

andrew s

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As @TheFlash says we should also not forget the actual D to A conversion process itself is in many cases operating at rf frequencies, is very close to the analogue section, and needs appropriate mitigation to prevent it contaminating the analogue signal. This doesn't explain why keeping other rf energy out of the DAC changes the sound.

Regards Andrew
 

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