jamesdyson
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Would it be fair to say that Amirs AP555 is now being outperformed by these top end dacs? It's limit being below 124dB.
Would it be fair to say that Amirs AP555 is now being outperformed by these top end dacs?
Hi jamesdysonWould it be fair to say that Amirs AP555 is now being outperformed by these top end dacs? It's limit being below 124dB.
Agreed. The AP ADC does also seem to be a limitation. It looks like the E1DA can also outperform it even without cross correlation.The DAC based generator in the APX555 is easily outperformed by many DACs, but the high perfrormance analogue sine generator in Amir's particular unit is, from what I can see, a particularly good one. THD is off the chart low. Noise is the limitation now.
The analyzer generators can of course drive to much higher levels (~26V) and that means there is gain. With gain comes some noise at those high levels.
Yes of course, the E1DA is not a complete measurement system and the AP does many additional and necessary things..
Concerning the APx 555 for the THD+N it's over for him,
but concerning the THD he is still in the race
with his system with 2 ADC + sliding filter,
in addition he does a lot of other things.
The AP does all this with proper input protection and gain ranging.Agreed. The AP ADC does also seem to be a limitation. It looks like the E1DA can also outperform it even without cross correlation.
Ideally, one would include the whole signal chain from the DUT downstream into the CC process, that is, effectively two identical channels strips with input stage, notch and makeup gain going into a stereo ADC to fully exploit CC noise reduction. As mentioned earlier, I don't know if APX series has dual notches and gain stages, though. The older range of analyzers don't.Anyway I think APx will have a bell ringing about
cross correlation and that the implementation is only a matter of
time .
Yes it does have many necessary features, but its clear that Amirs unit is at the top end of the AP ADC tolerance range but can't get past 124dB. Typical is 120dB. its pretty clear that its unable to measure the best DACs accurately. Steady sine or sweep. The signal generator is superb. Again Amirs does appear to be at the top end of the tolerance range but still doesn't get past 122dB.The AP does all this with proper input protection and gain ranging.
If it's about sine or sweeps, the tracking notch of the AP is a great feature.
If it comes to multitone, the E1DA ADC will likely beat it - for sure when using cross-correlation.
I understand your plots above, except the third one.Cosmos grade 0. 5 volt range. Smsl sux right channel.
CCA
View attachment 388422
CCM
View attachment 388423
CCM ADC noise floor input shorted
View attachment 388425
CCM. ADC 96KHz. Reduced signal to -0.5dB Also moved adc to reduce mains pick up.
View attachment 388426
That's simply measuring the ADC noise floor with its input shorted.I understand your plots above, except the third one.
What does that mean ?
A test with Virtins Multi Instrument 3.9.11
Source DAC D50 III Mono
997Hz 0dBFS 44.1kHz
ADC RME ADI-2/4 19dBu range
FFT Size 32k, Dolph Chebyshev 200
BW 20-20k Hz
AES-17 1 octave notch
View attachment 387115
Same with REW 5._40 Beta 50
View attachment 387113
As may be seen, both measure the same SNR (0.1dB difference is not significant)
REW is measuring lower THD and therefore gets higher SINAD (more in line with Notch measurementt)
REW also converges much faster.
But it's good to see this implemented in MI still.
Measuring the ADCs noise floor with cross-correlation straight away is not possible to my opinion. You need to account for the noise reduction = f(#averages).How could that work ?
And what figure are you looking at ?
-125.6 dBFS (A) ?
For a class 0, that should rather be -129dBFS (A)
Of course, it can't be -143.3dBFS A either
I really don't get it.
This would mean 2 sliding notch filters that match fairly well (phase is my concern in case the notch is deep).Ideally, one would include the whole signal chain from the DUT downstream into the CC process, that is, effectively two identical channels strips with input stage, notch and makeup gain going into a stereo ADC to fully exploit CC noise reduction. As mentioned earlier, I don't know if APX series has dual notches and gain stages, though. The older range of analyzers don't.
Of course. I didn't mean the adc chips themselves. I meant the cosmos without dac connected and with its xlr inputs shorted. If the noise of the 2 channels is primarily uncorrelated, would it not tend towards 24 bits 144dB?Measuring the ADCs noise floor with cross-correlation straight away is not possible to my opinion. You need to account for the noise reduction = f(#averages).
JamesDyson probably meant the noise floor of the acquisition system (in contrast to the noise floor with the DAC connected) ?
jamesdyson has a grade "0" ADCHow could that work ?
And what figure are you looking at ?
-125.6 dBFS (A) ?
For a class 0, that should rather be -129dBFS (A)
Of course, it can't be -143.3dBFS A either
I really don't get it.
View attachment 388517
jamesdyson has a grade "0" ADC
The noise curve represents, I think,
the measurement of the noise, with input at "0" in
stereo mode, this corresponds to 123.49dBFS / 125.6 dBFSA
Which corresponds to the noise for the cross correlation
measurement.
OK, so what we see us the amount of correlate noise between the 2 channels.I meant the cosmos without dac connected and with its xlr inputs shorted. If the noise of the 2 channels is primarily uncorrelated, would it not tend towards 24 bits 144dB?
This would mean 2 sliding notch filters that match fairly well (phase is my concern in case the notch is deep).
With software and thorough individual calibration this should be feasible.