manisandher
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- #41
There's a lot of speculation in the thread. Please can you explain what you did ASAP to clear this up. E.g. how do you do a null test with one DAC?
Done.
There's a lot of speculation in the thread. Please can you explain what you did ASAP to clear this up. E.g. how do you do a null test with one DAC?
Thanks for the explanation in post 2. Can you explain why you use variable output and how you compensate for the impact of this (e.g. is this an attenuator after the DAC or DSP volume contro)l?
Even with ASRC, it is required to know the incoming clock rate so the resampling can resample the incoming waveform at the correct times, and so you don't get buffer under or overflow.No, I mean in most DACs ESS chips freely spin off their own 100MHz crystal. And no, the DAC is certainly not required to recover the clock. Heard of ASRC, or perhaps FiFO reclock that some DACs use?
That's likely to make quite a big difference. These days digital attenuation is excellent, so much so that it should be inaudible, BUT in this case you are performing a null after setting the DAC to be non bit-perfect, which is unfair on the DAC. Use a proper analogue attenuator instead.I use variable output from the DAC (using the DAC's internal digital volume control) so that the RME is always presented with a similar-level analogue signal
That's likely to make quite a big difference. These days digital attenuation is excellent, so much so that it should be inaudible, BUT in this case you are performing a null after setting the DAC to be non bit-perfect, which is unfair on the DAC. Use a proper analogue attenuator instead.
Do neither! Make it bit-perfect end-to-end and adjust with an attenuator. You are comparing nulls between input and output, so don't mess with the bits in between or your experiment is invalidI disagree. It's trivial to show that the digital attenuation in a DAC is totally transparent.
Instead of using the DAC's internal digital volume control, I can set the DAC to max. output, and adjust the level of the 'reference' using Roon's 64-bit DSP. The nulls are identical.
Related to what KSTR said already, what you'll find is the null level is dominated by filtering differences. That is why sometimes a DAC with considerably better THD+N will give a less deep null. You have a couple options. One is to use 96 khz files and restrict analysis to 20 khz using Deltawave's filter. This reduces greatly the DACs filter effect in the audible band. Another is to allow Deltawave to correct for phase and FR differences. Doing this will greatly improve results. As this only happens if FR and phase are the differences it shows nothing exotic or unexpected is responsible though some don't like that you are correcting the DAC. Still you know what you are correcting.
Make it bit-perfect end-to-end and adjust with an attenuator.
Why? Roon's 64-bit DSP, and the DACs internal digital volume control are demonstrably totally transparent. No analogue attenuator is going to be anywhere near as accurate.
Related to what KSTR said already, what you'll find is the null level is dominated by filtering differences. That is why sometimes a DAC with considerably better THD+N will give a less deep null. You have a couple options. One is to use 96 khz files and restrict analysis to 20 khz using Deltawave's filter. This reduces greatly the DACs filter effect in the audible band. Another is to allow Deltawave to correct for phase and FR differences. Doing this will greatly improve results. As this only happens if FR and phase are the differences it shows nothing exotic or unexpected is responsible though some don't like that you are correcting the DAC. Still you know what you are correcting.
While it won't have a huge impact, even a perfect digital volume control will only attenuate the main output signal from the DAC, it will not touch noise. As a result applying any digital attenuation will decrease SNR by the amount of digital attenuation, no way around this. Assuming all DACs have roughly the same output level I don't think a few dB of attenuation is a big deal, especially if you haven't corrected magnitude / phase response.
Michael
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There will be conversion to analog, digitizing and digital volume adjustment (in Deltawave).Do neither! Make it bit-perfect end-to-end and adjust with an attenuator. You are comparing nulls between input and output, so don't mess with the bits in between or your experiment is invalid
Why?The differences between filters, well down below 500Hz in some cases, is amazing.
So the null will tell hardly anything about SINAD.
Your file has a lot more energy in mids than in highs.
Does this impact the spectra? ∆ is low in highs because the there is no signal?
And yet, some DACs/filters are substantially worse in the lows, mids and highs - and not just the highs as a simple FR might suggest.
It does not show the filter. It does show the change in phase with phase EQ and without.I've never used the Deltawave EQ, but have used other EQ while doing Deltawave testing to greatly improve nulls. I assume it develops a single magnitude / phase correction filter and then it applies it to the entire analysis? Does it show the response of the applied filter?
Michael