as an example, I see some clue of IMD at intermediate level in mono mode. To be true, this is because noise is so low, so not really a concern) There are two color changing LEDs right next to the XLR connectors, which indicate whether the ADC runs in stereo or mono mode. 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. Customers are to bear the consequences and fees incurred, if the parcel was undelivered due to any of the following situation: As you noted, what's happening here is that the graph shows a +60dB gain applied to the noise floor. So if we look at 17kHz and that -89dB noise, it's actually -89-60dB=-149dB.

In the picture above, we can see that the main inputs for the ADC are the dual balanced XLR connectors. Notice that the markings indicate that they can have input levels up to 10Vrms (+22dBu). The input level can be adjusted to optimize the dynamic range when you're measuring devices of lower voltage. You adjust this with some DIP switches at the bottom of the unit (I have been told that these are high-quality gold plated switches, guaranteed for minimum 1000 cycles): REW https://www.roomeqwizard.com/ free for a single-channel version, that's enough for most cases. Not all versions correctly work with THD+N but RC9 at least is ok. The known issue is ASIO only supported, ASIO4ALL works ok but up to 192K. Sometimes ASIO4ALL driver can occupy Windows 10 volume slider after use, which makes it impossible to change the MONO/STEREO mode of ADC. Another nice option for REW is FlexASIO with 32/384 https://github.com/dechamps/FlexASIO/releasesA generator (Ri 200 Ohm, 1 kHz) is connected to ADCiso(Left) or ADCiso(Right) via XLR cable. The ADCiso is in Mono Mode. Measurements are made with REW (OS Ubuntu), voltage values are now normalised. Here is an FFT of an A-grade E1DA Cosmos ADC with nothing plugged in. The settings are unreasonable; 160 averages of 4M Length: about 2 hours of data collection. This was taken with input set to 1.7V, mono mode (summing both channels). Using ASIO4All - note Cosmos ADC as input. For the record,I'm using REW 5.20 RC9 currently. I haven't updated in a few months as this version has worked well for me thus far. Ivan warned that some builds might have accuracy issues when calculating THD(+N) so be mindful of any unusual results. As you can see by comparing the 2 measurements above (the second, with 122dB SINAD, being done with the E1DA ADC), this may limit the output level of the DAC.

A-weighted noise is -128.6dBFS, matching the specs for an A-grade unit. I get the same value with the input set to 10V or 1.7V. At the 1.7V setting this corresponds to noise below 1µVrms. The noise floor being below -126dBFS at all input levels rivals the APx555. Unlike the APx555, the Cosmos cannot autorange, so for measurements like sweeps the APx555 still has superior performance. is below 1nV; the flat noise spectrum of the Cosmos ADC means that picovolt level signals can potentially be measured at any audio frequency with sufficient FFT lengths, provided they are narrow enough bandwidth (4M FFT length means ~0.01Hz bins).E1DA Cosmos ADC is a high-performance Analog-to-Digital Converter that can be used for measurements of ultra-low THD+N signals or calibrating Desktop DAC's for minimum distortions. E1DA has professionally designed the Cosmos ADC with premium ESS Sabre ADC Chip. It can also be used to measure the performance of high-fidelity desktop DAC systems with great precision. High-Performance ADC Chip From Sabre Technologies:-

The calibration is performed at the particular ambient temperature 27C, if your environment is seriously colder/hotter the THD performance is not guaranteed. Every time the unit needs to be warmed up during 15-20min before use. Fact is that I recently entered that world of measuring devices, and that's how I got to read your blog. I'm into older vintage devices, you know these old gears that some audiophiles praise more than any new garbage cheap Chinese stuff :-) I wanted to test that myself, and it's amusing to measure 40 years old unserviced devices.The default numbers for 2nd and 3rd harmonics were calibrated prior to the unit being sent to me to correspond to results on the Audio Precision SYS27XX with a -0.5dBFS signal. You can also change which filter setting is applied to the ADC channels; "Linear phase apo" and "Linear phase fast" both worked well in my testing. If it is plastic sealed when you get it, it should remain plastic sealed. Some types of goods such as CIEMs and custom cables cannot be returned. The RME ADI-2 Pro is fantastic and I don't think you need to upgrade for 40-year old vintage gear! It provides for a ton of features including the adjustable input level, balanced, mono processing, etc. If you can afford it, the RME, especially with the APU when required, remains the top choice for measurerments, IMO. THD@[email protected] BW 22-22kHz <.00003%(.3-.2PPM) typical for 32b/48kHz all harmonics level -135-145db