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E1DA Cosmos ADC

trl

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Absolutely no problem, just make a 3- wire RCA to XLR cable. Low distortion remains same.
Thanks Pavel, but I think my concern was related to the low input impedance of the Cosmos ADC when used in unbalanced operation.
 
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pma

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Thanks Pavel, but I think my concern was related to the low input impedance of the Cosmos ADC when used in unbalanced operation.
You are right, in some cases I have to use a buffer in front of E1DA Cosmos. It is not a universal unit and needs qualified operator. But it is good for measurements of power amplifiers, as they have extremely low output impedance and in parallel with usual 4 or 8 ohm load the input impedance of Cosmos is negligible and low impedance dividers can be used.
 
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Music1969

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THD+N 6db mismatch at 1kHz -116db. BTW, REW seems adjusted only for 1k THD+N and >1k or <1k THD+N are also wrong, at 100Hz AP2700 6-7db better! I gonna test Arta at 100Hz and 6kHz.
PS: no, regarding REW it was my mistake because FFT was 64k and spectral leakage made 100Hz THD+N so bad. At 6kHz REW shows 1db less THD+N vs AP2700, similar to Arta.
Hi @IVX

I am getting Right channel of Cosmos ADC 6dB higher in level than Left channel

REW shows the input signal 6dB higher for right channel

I checked the files many times, both files are same level when I look in Audacity.
 

staticV3

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@Music1969 your Cosmos is in Mono mode:
Cosmos_Mono_vs_Stereo.png
You should also see that the signal LEDs next to the XLR inputs light up blue when a signal is present. Blue=Mono, Green=Stereo.

You change modes via the Volume slider.
2022-02-14_23-21-31.jpg Screenshot_2023-03-06_at_17.24.02.png

If you're on Windows, then you first have to install the driver: Link
On Linux and macOS, no driver install is required.

On Windows, you can also change modes using the Cosmos_Tweak utility: Link

Windows and macOS will remember the mode that you set between reboots and disconnects. So if you only ever use Stereo mode, then it's enough to set the Cosmos to Stereo once. Afterwards it'll stay in Stereo.

If your Cosmos is in Stereo (green LEDs) and you still have different levels, then it's possible that you have set different input sensitivities for each channel using the DIP switches at the bottom of the unit.
Or something's wrong with your DAC. Or with your cables.
 

Music1969

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You should also see that the signal LEDs next to the XLR inputs light up blue when a signal is present. Blue=Mono, Green=Stereo.
Ah yeh I am blue
Thanks

I remember the measurements are a little more accurate in mono mode, correct ?

Edit : 3dB better SNR in mono according to product page
 

staticV3

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Ah yeh I am blue
Thanks

I remember the measurements are a little more accurate in mono mode, correct ?
Mono mode increases the Cosmos' SNR by 3dB.

Keep in mind that in Mono mode, you have to connect One output channel of your DAC to both inputs on the Cosmos.

Also keep in mind that doing so will halve the load impedance that your DAC has to drive. That can cause issues depending on the DAC.
 

Music1969

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Mono mode increases the Cosmos' SNR by 3dB.

Keep in mind that in Mono mode, you have to connect One output channel of your DAC to both inputs on the Cosmos.

Also keep in mind that doing so will halve the load impedance that your DAC has to drive. That can cause issues depending on the DAC.
Ive been doing measurements with only 1 channel connected

So i have not been betting the true benefit of mono mode?

in other words, same performance as stereo mode?
 

mdsimon2

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Mono mode increases the Cosmos' SNR by 3dB.

Keep in mind that in Mono mode, you have to connect One output channel of your DAC to both inputs on the Cosmos.

Also keep in mind that doing so will halve the load impedance that your DAC has to drive. That can cause issues depending on the DAC.

Exactly this. I only use mono mode for dynamic range measurements as you often end up with worse results than stereo mode if making full scale measurements as many DACs do not like halving the already low input impedance caused by the splitter.

I've found that when making full scale THD+N measurements there is often a sweet spot. For noise performance you want to use the lowest sensitivity as possible but this also results in the lowest input impedance which is bad from a distortion standpoint. I've often found that a slightly higher sensitivity gives the best results as distortion is reduced while not compromising noise too much.

Michael
 

staticV3

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Ive been doing measurements with only 1 channel connected

So i have not been betting the true benefit of mono mode?

in other words, same performance as stereo mode?
With the Cosmos in Mono and signal only present on R input, the R output is identical to if the Cosmos had been set to Stereo. See here:
Cosmos_Mono_vs_Stereo.png
The L output will have 6dB lower signal and 3dB lower noise, so in total 3dB less SNR.

With the signal only present on L input, the L output will have 6dB lower signal and 3dB lower noise, so in total 3dB less SNR.

And R output won't output anything regardless of Mode.
 

IVX

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Exactly this. I only use mono mode for dynamic range measurements as you often end up with worse results than stereo mode if making full scale measurements as many DACs do not like halving the already low input impedance caused by the splitter.

I've found that when making full scale THD+N measurements there is often a sweet spot. For noise performance you want to use the lowest sensitivity as possible but this also results in the lowest input impedance which is bad from a distortion standpoint. I've often found that a slightly higher sensitivity gives the best results as distortion is reduced while not compromising noise too much.

Michael
there is some trick to measure SN/DR at a lower level than Cosmos ADC may offer i.e. subresidual noise.
 

staticV3

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there is some trick to measure SN/DR at a lower level than Cosmos ADC may offer i.e. subresidual noise.
mdsimon was talking about full-scale THD+N measurement and the challenge of high load impedance with the Cosmos, especially in Mono.
 

Music1969

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With the Cosmos in Mono and signal only present on R input, the R output is identical to if the Cosmos had been set to Stereo. See here:
View attachment 273784
The L output will have 6dB lower signal and 3dB lower noise, so in total 3dB less SNR.

With the signal only present on L input, the L output will have 6dB lower signal and 3dB lower noise, so in total 3dB less SNR.

And R output won't output anything regardless of Mode.
Thanks !

Very helpful
 

Music1969

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Keep in mind that in Mono mode, you have to connect One output channel of your DAC to both inputs on the Cosmos
At the moment I am measuring from my headphone amps XLR-4 output

It splits off into left and right XLR-3 for measuring with Cosmos ADC

In this case I can't really connect DAC left output to AMP L+R output ?

Unless I misunderstood what you wrote here (quoted)

I can connect both left and right to Cosmos and can play L+R signal at the same time from REW - will that achieve what you wrote or not really? For optimising mono measurement
 

staticV3

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In this case I can't really connect DAC left output to AMP L+R output ?
Nobody's talking about the DAC to AMP connection.
Unless I misunderstood what you wrote here (quoted)
Yeah I think you did
I can connect both left and right to Cosmos and can play L+R signal at the same time from REW - will that achieve what you wrote or not really? For optimising mono measurement
No. If you want to do Mono measurement with the Cosmos, then don't connect L out to L in and R out to R in.
Instead, you should connect L out to L in and L out to R in. One output (L) to both inputs (L+R).
 

Music1969

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Instead, you should connect L out to L in and L out to R in. One output (L) to both inputs (L+R).
Not really possible with XLR-4 to dual XLR3 adapter right?

I would need to add another single XLR-3 to dual XLR-3 cable to do this?

Even for a normal DAC connection to Cosmos, an XLR-3 to dual XLR-3 is required? For this mono measurement
 
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