Hmm, I'm far from being an expert, but I always thought that upsampling and oversampling are the same thing. The only difference is that upsampling uses a certain value like 96 kHz (for example 44.1 gets upsampled to 96) and oversampling uses multiples (2x, 4x, 8x) of the native value. I think the DAC has 8x oversampling (can MC confirm that?) and that would mean that 44.1 kHz material gets indeed "upsampled" to 352,8 kHz. Am I correct or not?
I am planning to buy the DAC and use it with a CD-transport with 44.1 kHz material only and I want to be sure that it gets the best out of my beloved shiny discs.
Upsampling is the process of increasing the sample rate of signal. Oversampling is interpolation to a higher sample rate, i.e. it includes a low pass filter corresponding to the passband of the original sample rate. Thus oversampling is one kind of upsampling.
MC's post makes clear what he meant by it.
There is an 8x interpolator on the AK4490 chip used in the DAC (https://www.akm.com/global/en/products/ … /ak4490eq/, bottom). EDIT: However, the new revision uses AK4493 which also uses 8x interpolation (https://www.akm.com/content/dam/documen … tbrief.pdf).
The signal sampled at 44.1 kHz would thus be upsampled to have a sample rate of 352.8 kHz but a low pass filter removes some of the components above 22.05 kHz (the Nyquist-frequency of a signal sampled at 44.1 kHz). The ideal (read: theoretically correct) low pass filter would reject (infinitely attenuate) any components above 22.05 kHz while allowing those below to remain at unchanged amplitude, i.e. the brickwall filter at the Nyquist-frequency. However, this filter is impossible to implement so a compromise between rejection of components above the Nyquist frequency and attenuation of frequencies close to but below the Nyquist frequency must be found. This is where the several filters in the DAC come from.
The perfomance of the DAC's filters at 44.1 kHz is shown in the manual on page 56 (v1.8 EDIT: using AK4490) or 57 (v2.0 EDIT: using AK4493) and here EDIT: for the ADI-2 Pro FS using AK4490
Source: http://archimago.blogspot.com/2018/09/m … s-dac.html.
Manual v1.8: https://archiv.rme-audio.de/download/adi2dac_e.pdf
Manual v2.0: https://www.archiv.rme-audio.de/download/adi2dacr_e.pdf
Something seems to be in the works with that Short Delay Low Dispersion filter. It's not available with FW 33 on my DAC. More on this here: https://forum.rme-audio.de/viewtopic.php?id=29596.
EDIT: It's for a revised version of the DAC using an AK4493 rather than an AK4490.