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E1DA Cosmos ADC

mansr

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@IVX kindly sent me a sample of the new Cosmos ADC to try out. Here are my impressions of it so far.

The Cosmos is housed in a compact metal case with rubber feet, USB Type C connector on one and dual XLR inputs on the other. Power is over USB only. Beside the USB connector is small LED that flashes slower or faster to indicate the current sample rate. Two LEDs next to the XLR inputs appear to indicate presence of a signal. The input sensitivity is set by a bank of DIP switches on the bottom of the unit.

On the USB side, the Cosmos appears as a 2-channel input device with the usual sample rates up to 384 kHz and a choice of 16-bit, 24-bit, or 32-bit sample size. The ALSA mixer interface presents two gain controls and a toggle which somewhat confusingly select between stereo and mono mode, the latter providing a (theoretical) 3 dB reduction in noise level.

Unfortunately, I do not have a signal source clean enough to test the true performance of this ADC. Some useful information is nevertheless possible to obtain. Firstly, we can look at the recorded spectrum with no signal.

1633095486975.png


Aside from a slight DC bias, this is as clean as it gets. There is not a hint of USB packet noise or power line hum. Above 100 kHz, we do get a rising noise level from the sigma-delta modulator. There is also a very slight noise spike near 156 kHz.

Recording the same signal on both channels, the levels match to within 0.01 dB, much better than most DAC outputs.

Just to get another graph, here's the spectrum of a 1 kHz tone played on a cheap audio interface, though this obviously says more about the DAC than the ADC:
1633097331692.png


The Cosmos ADC does have one drawback in that the input impedance is relatively low, ranging from 640 Ω to 3.5 kΩ (measured at 1 kHz) depending on the the sensitivity setting. This may be too low for some sources.

That's all I have for now. I'll update if I think of any more relevant tests to perform. Suggestions are of course welcome.
 

bennetng

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How about passband ripple? One thing I don't like about the recent AKM ADC chips is the ripple, like this. See the reply with a member testing a MOTU in the post right below it.

Since you have the UH-7000 with a PCM4220 with low ripple, it can be used as a reference when measuring other DACs or audio output sources.
 

MC_RME

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It ripples more than anyone likes. Not as bad as the AK557x, but still more than necessary.

Regarding the DC offset: this seems to be a bug in the chip itself. It includes the usual high pass, but that one is unusable as it cuts off at 100 Hz :facepalm:. So one needs to add a DC filter in the digital domain to get rid of this DC offset - it seems. If anyone knows differently please tell.
 

HiZ

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Thanks to you, I got to know a great product. I enjoyed watching it.
 

HiZ

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It ripples more than anyone likes. Not as bad as the AK557x, but still more than necessary.

Regarding the DC offset: this seems to be a bug in the chip itself. It includes the usual high pass, but that one is unusable as it cuts off at 100 Hz :facepalm:. So one needs to add a DC filter in the digital domain to get rid of this DC offset - it seems. If anyone knows differently please tell.
Oh, thank you so much for answering the HDSPe question last time. I didn't get to say thank you. I solved the problem well with the way you told me!
 

Tom C

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You neglected to include the single most important measurement. Cost.
 

Tks

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Does input impedance have anything to do with the input buffer (if there even is one).
 

phoenixsong

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Measurements from Wolf in addition to those by Archimago
 

phoenixsong

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Haven't seen any link from Archimago's website yet, so: http://archimago.blogspot.com/2021/09/early-look-e1da-cosmos-adc-affordable.html.

Besides the linearity, all the measurements are very good indeed. Great job!
Oops I didn't realise how new this thread is! Kudos to @mansr for starting it, it is one worthy device. Personally I'm thinking of using my mics with it for gaming/streaming etc, but it doesn't seem that straightforward. Will it work with say the SeElectronics V7x>Dynamite DM1>Cosmos ADC? I assume monitoring and gain setting functions will all have to be controlled from PC
 

trl

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I don't think this ADC is intended to be used in professional audio, although with an added Phantom power and a decent DAW you could probably do your thing and with a very good audio quality too.

L.E.: I don't think Cosmos has internal microphone gain, nor mic input, so the input impedance may not fit a regular mic. An external mic-pre will still be needed, so output results will be influences by the external preamp.
 
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mansr

mansr

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The Tweak Cosmos application (Windows only, sadly) allows configuring the anti-alias filter to use with several linear and minimum phase options. To test these, I used an input consisting of white noise high-pass filtered at 24 kHz recorded with a sample rate of 48 kHz. The graph below shows the result with the various linear phase choices. For reference, the blue trace shows the same input recorded at 384 kHz.

1633970560187.png
 

Grooved

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I don't think this ADC is intended to be used in professional audio, although with an added Phantom power and a decent DAW you could probably do your thing and with a very good audio quality too.

L.E.: I don't think Cosmos has internal microphone gain, nor mic input, so the input impedance may not fit a regular mic. An external mic-pre will still be needed, so output results will be influences by the external preamp.

I would better than it's not intended to be used in "home studio" setup, where most people will want to find a device with ADC-DAC and at least a mic preamp, or more... but in professional, with any audio interface, it's a common thing to only use the line input of the interface ADC with external mic preamps, so this would be perfect. The only negative point for recording would not be it's features but the fact that there's only 2 inputs, while 2 inputs only would is perfect for mastering (with sync added from the I2S) or do a stereo live record.
 
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mansr

mansr

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Here's the other half of that, the passband performance of those filters. Same setup as before, except now the input contains only frequencies below 24 kHz. That way, the aliases produced by some of the filters will have no effect.

1633994264180.png
 
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mansr

mansr

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This is what the Tweak application looks like:
tweak.png


While experimenting with the ADC, I noticed a few things regarding the user interface that I think could be improved. Firstly, there is no error indication if settings are changed without first pressing the the "Connect&Read" button or if the ADC has since been unplugged. Secondly, the filter selection would be easier to operate if it simply consisted of four drop-down menus, one for each ADC.
 
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