DAC for industrial vibration data

[Blumlein 88]

Happy to be corrected. So what you are saying is the current crop of cheap Topping/RME/SMSL DACs will output a 1Hz sine at 0dBFS at full rated output voltage (same as 1kHz)?

At what point do these supposedly properly designed source products pull the pin? (0.5Hz?) You cannot be inputting DC out of a DAC.

For an RME Babyface Pro FS in loopback. It is fully flat to 20 hz. Is about .05 db down at 10 hz. Only about .1 db down at 8 hz though the level is slowly fluctuating. I don't know if it is some sort of DC offset or what is causing it. By 5 hz more fluctuating which averages out to about .35 to .4 db down. At 1 hz there is lots of fluctuation with an 4 sweep average over 128k fft of a bit over - 7db. I of course don't know how much is the ADC or the DAC.

Using the Topping D10 Balanced for the DAC portion the results are the same almost exactly. So maybe the ADC is what is limiting below 20 hz. So both DACs must be pretty close to flat to at least 10 hz. Maybe lower if the ADC is the bottleneck below 10 hz.

 

[staticV3]

@Blumlein 88 do a stepped THD vs Frequency sweep instead of the standard measurement sweep. No fluctuations that way.

 

[mansr]

Happy to be corrected. So what you are saying is the current crop of cheap Topping/RME/SMSL DACs will output a 1Hz sine at 0dBFS at full rated output voltage (same as 1kHz)?

At what point do these supposedly properly designed source products pull the pin? (0.5Hz?) You cannot be inputting DC out of a DAC.

Why should a DAC not do what it's told?

 

[restorer-john]

For an RME Babyface Pro FS in loopback. It is fully flat to 20 hz. Is about .05 db down at 10 hz. Only about .1 db down at 8 hz though the level is slowly fluctuating. I don't know if it is some sort of DC offset or what is causing it. By 5 hz more fluctuating which averages out to about .35 to .4 db down. At 1 hz there is lots of fluctuation with an 4 sweep average over 128k fft of a bit over - 7db. I of course don't know how much is the ADC or the DAC.

Using the Topping D10 Balanced for the DAC portion the results are the same almost exactly. So maybe the ADC is what is limiting below 20 hz. So both DACs must be pretty close to flat to at least 10 hz. Maybe lower if the ADC is the bottleneck below 10 hz.

Absolutely your ADC is killing it. All audio ADC will have HPFs (caps) to prevent DC offsets taking out or assymetrically destroying the ability to capture full level swings

 

[restorer-john]

Why should a DAC not do what it's told?

When an audio DAC sends DC to the next stage because it is poorly designed. I'm all about wide bandwidth, but source components outputing DC, strapped into a system with a heap of gain is no good for all the following stages, especially if they are 'pure' DC coupled designs.

 

[mansr]

When an audio DAC sends DC to the next stage because it is poorly designed. I'm all about wide bandwidth, but source components outputing DC, strapped into a system with a heap of gain is no good for all the following stages, especially if they are 'pure' DC coupled designs.

If something can't handle DC, it should be blocking it, not relying on something else to do it.

 

[Sokel]

When an audio DAC sends DC to the next stage because it is poorly designed. I'm all about wide bandwidth, but source components outputing DC, strapped into a system with a heap of gain is no good for all the following stages, especially if they are 'pure' DC coupled designs.

That's what a dirt cheap 15yo dac does.
What is interesting is that in 0-20000Hz measurements the THD+N is elevated cause it includes the 0-20Hz stuff.

Edit:The same measurement with peak level included to see what sends to the next device.

 

[restorer-john]

If something can't handle DC, it should be blocking it, not relying on something else to do it.

What a stupid argument.

Any audio source that does output significant DC is faulty by design.

 

[restorer-john]

That's what a dirt cheap 15yo dac does.
What is interesting is that in 0-20000Hz measurements the THD+N is elevated cause it includes the 0-20Hz stuff.

View attachment 232129

Consider a DC offset will throw your ADC out so far, it cannot determine any remotely useful THD information.

That is why we AC couple for distortion measurements.

 

[Sokel]

Consider a DC offset will throw your ADC out so far, it cannot determine any remotely useful THD information.

That is why we AC couple for distortion measurements.

Total newbie in measurements,I'm at the elementary stage still.
But is fun!

 

[Sokel]

And that's the spectrum of 5Hz.

 

[Sokel]

Consider a DC offset will throw your ADC out so far, it cannot determine any remotely useful THD information.

That is why we AC couple for distortion measurements.

Seems that it is AC coupled:

 

[Blumlein 88]

Here is a 1 hz to 41 hz sweep for the Topping D10B feeding the Babyface.

And the Babyface in loopback to itself.

 

[Trouble Maker]

When I see one of these threads, I'm usually a little confused.

What are you trying to solve with a consumer product that couldn't be (better) solved with an industrial one?
Is it just a cost issue? If so, I get it. But you'll likely spend more (money) time than the cost difference using an ill suited product due to inefficiencies. You also may introduce possible points of human error. It seems like it introduces too many possible issues/what ifs, that a commercial product designed for this purpose doesn't have.

If you have many files to process, depending on what kind of input system you are using, you may be able to automate the process too. This could save a ton of time.

There are probably dozens of companies with collectively hundreds of technical sales associates who will happily point you towards the right product for your situation.

The NI cRIO/cDAQ stuff can be pretty economical.

Voltage out and multi i/o (includes analog out) modules. The specs or ranges of specs seem more varied on the Voltage Out modules, but the multi I/O gives you room to grow for future projects.

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You'll need to put them in a chassis, the cRIO single slot is probably the cheapest.

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Edit: Also, is there not a way to view/process the files you already have, or do some kind of file/data conversion process into the new system/file type? Honestly speaking, this (digital file to analog out to another systems analog in to....?) seems like not a great way to do what you seem to be trying to do.

 

[Blumlein 88]

Okay, using my trusty multimeter. Results mirror those of the ADC. Both DACs are putting out fluctuating levels at 10 hz and below. Best I can tell with the meter readout floating around, it is about the levels shown. The fluctuation is minimal at 10 hz and gets greater the lower in frequency you go. So neither DAC goes near DC well.

FWIW, my meter showed 4.18 volts for the D10B at 1 khz while Amir recorded 4.236 volts. For the Babyface Amir had 4.086 volts with my meter showing 4.03 volts. Both less than 2% off though of course the DACs could differ some as well.

 

[mansr]

Okay, using my trusty multimeter. Results mirror those of the ADC. Both DACs are putting out fluctuating levels at 10 hz and below. Best I can tell with the meter readout floating around, it is about the levels shown. The fluctuation is minimal at 10 hz and gets greater the lower in frequency you go. So neither DAC goes near DC well.

FWIW, my meter showed 4.18 volts for the D10B at 1 khz while Amir recorded 4.236 volts. For the Babyface Amir had 4.086 volts with my meter showing 4.03 volts. Both less than 2% off though of course the DACs could differ some as well.

Which multimeter, and what exactly are you measuring?

 

[KSTR]

Here is a 1 hz to 41 hz sweep for the Topping D10B feeding the Babyface.
[...]
And the Babyface in loopback to itself.

Incorrect measurements.

Okay, using my trusty multimeter. Results mirror those of the ADC. Both DACs are putting out fluctuating levels at 10 hz and below.

Incorrect as well.

You cannot measure way below 10Hz with a typical logsweep (it needs to have special properties for this) and you cannot use a simple multimeter for that, they are not designed to do that.

Use a DC-coupled ADC (only few are DC-coupled, I've modded my RME ADI-2 Pro) or just simply an oscilloscope which is as bullet-proof as it gets.
You will see there is no fluctuation. I do know 100% for sure that the D10B puts out DC (and any low frequency) perfectly.

 

[KSTR]

Absolutely your ADC is killing it. All audio ADC will have HPFs (caps) to prevent DC offsets taking out or assymetrically destroying the ability to capture full level swings

Any audio source that does output significant DC is faulty by design.

You do see you own inconsistency, don't you? Why would an ADC need coupling caps when it's connected to a non-faulty source?

 

[Blumlein 88]

Incorrect measurements.

Incorrect as well.

You cannot measure way below 10Hz with a typical logsweep (it needs to have special properties for this) and you cannot use a simple multimeter for that, they are not designed to do that.

Use a DC-coupled ADC (only few are DC-coupled, I've modded my RME ADI-2 Pro) or just simply an oscilloscope which is as bullet-proof as it gets.
You will see there is no fluctuation. I do know 100% for sure that the D10B puts out DC (and any low frequency) perfectly.

Did not use a log sweep. Used individual tones with meter and ADC. So why does a multimeter read 15 hz and not 10 hz? And also same for ADC ? I would like to know why it is acting like this. The way Multitone does sweeps isn't really a sweep. It generates individual tones for a few seconds with log spacing. I also made long steady tones with the same results.

 

[Blumlein 88]

Which multimeter, and what exactly are you measuring?

Using Topping D10 Balanced and DAC side of Babyface. Tried outputs from Multitone, Reaper, and Audacity. Meter in this case was an old RadioShack DMM. ADC was a Babyface Pro FS. Just tried the same with an old Simpson 260 analog meter. The 260 is specced to be flat down to 10 hz. It read to a slightly lower hz though you could see the needle quivering. At 5hz and below it was swinging about considerably. Would use an Oscope, but don't have one handy. My analog Tektronix is in storage.

So I would like to know why things are acting this way.

Also what signal is being fed to the DAC for DC? @KSTR