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While the Cosmos ADC is capable of greater resolution used on its own, when paired with the APU, the RME is more convenient with its user interface and better on-screen information. For example, the ability to change input reference levels between +4/+13/+19/+24dBu along with the RME's auto-adjust levels feature when input gets too high are very nice benefits. to preserve the original ESS ADC chip performance as high as possible and keeping the cost under tight control, the ADC utilized a direct FDA front end with different input impedance across the gain ranges. It makes voltage drops at the DUT outputs if one has a relatively high output impedance and minimal ADC input range selected(1.7V, see the specs), I did mention that above and have just repeat it again. One "controversial" characteristic to this design which I need to add here (as you can see in the comments, I had neglected to do so in the first release of this article), is that this device does not incorporate an input buffer which results in variable and relatively low input impedance. Here's how it looks like depending on the voltage dip switch settings: 1.7V (6.83dBu) = 640Ω2.7V (10.85dBu) = 1kΩ The very last release of REW, v5.20.9, even allows to display the frequency range taken into account for the fundamental. That's genious !) Notice the single USB-C connector, there's a small amber LED that blinks when in use. The blinking rate is dependent on the sample rate: 48kHz = 0.5Hz (1 blinks/2s), 96kHz = 1Hz, 192kHz = 2Hz, 384kHz = 4Hz, and the 44.1kHz family blinks slightly slower by about 10% (ratio 44.1/48 x frequency).
THD@[email protected] BW 22-22kHz<.00003%(.3-.2PPM) typical for 32b/48kHz all harmonics level -135-145db Even though I show those extra frequencies, the THD+N measurement applies filtering between 20Hz to 20kHz so that 24kHz noise will not be applied to the final calculation (as you can see, the areas beyond 20-20kHz on either end faded out to indicate this). With a -60dBFS 1kHz signal, the harmonic levels are extremely low, so the |THD+N| result is basically a reading of the full RMS noise level which we add 60dB to to get the dynamic range - this summed amount is why we see a number like 123.9 rather than something lower as you would see with each frequency in the graph being down -130dB or less. But, why does it work this way?? Is it a Topping DAC thing or an REW thing? The levels didn't change. Windows 10 doesn't need the driver but Windows 7 does and the driver installation may require manualinstallation. So, if you are not ready for that the good idea just update W7 for W10. To measure THD+N (or SINAD), measure the fundamental over 1/2 octave below the fundamental frequency and 1/2 octave above.So in the last year, I have been using the Cosmos ADC more when needed with the higher resolution DACs like the SMSL DO100:
I'm not super familiar with what the APU is going to be, but for my uses I'm generally interested in both the noise floor at different frequencies, as well as distortion at different frequencies. This applies for most countries. However, large items such as headphones and desktop DAC/AMPs (e.g. HarmonicDyne G200, MUSICIAN MDP-2, and etc.) are excluded. The mains noise is a barely visible -184dBFS blip at 60Hz; not remotely measurable in any reasonable test suite. This is plugged into the front USB port on a desktop PC, and with the input impedance set to 640Ω. The second and biggest half of Cosmos APU is the 1/10kHz active notch filter with -30db ratio(Q about 50) at the fundamental frequency and nearly 0db at 2nd and 3rd harmonics i.e. you can simply divide by 30(or subtract 30db) the THD/THD+N result to get a normal value. Also, with REW or Arta, you can use a calibration file to normalize the notch's frequency response and observe FFT results directly. The max balanced input level is 10Vrms, it is also clamped but by the active clamp with opamp's rail voltage-1V, hence, 10ohm 0603 again may be burned like a fuse. The residual harmonics of the distortions are <-150db@1kHz or <-130db@10kHz, that's probably isn't too spectacular but still better than APx555. The residual THD+N, practically achieved one, -132db@1kHz@10Vrms(DAC+LPF approach), calculations based one is -134db but I can't confirm that so far because of can't find a perfect-zero-noise sine for that It is clear that APU is kinda a microscope for your ADC, even any laptop audio input with APU gets the ability to measure a tiny noise of DACs or LDOs, and distortion levels are perhaps lower than AP SYS2722 or even Cosmos ADC. A couple of days ago I noticed that during the calibration Cosmos ADCiso has no green/blue/red LEDs indication, in about 30% of cases.
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From that perspective the Cosmos ADC is not an ideal choice for this use-case, as you need an additional box to make it work well. Shorting" the input makes the mains noise disappear but otherwise has no significant effect on the noise level. This was taken using a 10.4Ω balanced dummy load to ground, on the 10V input setting. If I had to guess, it looks like the mains noise is dominated by bias/leakage current over the input resistor. Levels this low indicates that the OPA2156's more robust input specs (aside from noise) compared to the OPA1612 wouldn't have any practical advantage as the input in this scenario.
Input Range: 1.7Vrms 640Ω, 2.7Vrms 1kΩ, 3.5Vrms 1.3kΩ, 4.5Vrms 1.66kΩ, 6.7Vrms 2.46kΩ, 7.6Vrms 2.82kΩ, 8.5Vrms 3.12kΩ, 10Vrms 3.48kΩ, 43Vrms 13.6kΩ. As I mentioned above, with +60dB pre-amp gain, be careful not to feed an excessively high signal into the APU - keep inputs to <3.5Vrms on the pre-amp side, and <10Vrms into the notch function to avoid potential damage. Also be mindful of the +48V phantom power when you're not plugging in a microphone! use not following the ‘User Guide’ or any additional safety, use, or warnings included in the product materials.
Apple cancelled this, now what?
Given the existing measurements performed already by @Archimago ( http://archimago.blogspot.com/2022/05/early-look-cosmos-apu-high-performance.html) and @WolfX-700 ( https://www-l7audiolab-com.translat...l=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp) it makes no sense for me now to upload my own measurements here, but I got similar figures as they did, so this APU really shines and makes a great addition to anyone needing a cheap device to "upgrade" an existing ADC. 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.
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