DAC Hat vs. Other DAC?

[TheOldPresbyope]

Hi,

I have the IQ Audio DAC hat/rpi4 set up. 

I don’t have the deep knowledge in regards to the technical side of this.
I read some posts mention USB is dirty noise wise and affects sound quality.
In what application would this apply? PC to DAC?

For the rpi and DAC hat, communication via I2S. If one plays music from
USB flash drive or USB SSD, does this USB noise still apply?

If you have experienced the DAC hats vs. standard DAC like Topping D10 or
SMSL SU-8, SU-9, is the Sound Quality night and day differences? Or subtle
improvements?

Right now I’m considering the Allo Boss 2 but not sure what I would gain
from it vs. the IQ Audio or trying the SMSL DAC which is 4x price of the DAC hat.

Thanks

Since you seem to be asking specifically about i2S vs USB -

I have used i2S products such as the HifiBerry DAC+ and DAC+ Pro and similar. I have used USB products such as the Khadas Tone 1 Board and the Creative BT-W2 (a USB-> Bluetooth -> headphones adapter).

Are there differences I can discern in their apparent sound qualities? Sure. Are these differences due to "USB noise"? No. They are due to the different design decisions made by the vendor, particularly in the post-DAC audio filters. This is true even between different i2S products or between different USB products. And, no, the differences are not "night and day"; they are subtle and, after a few minutes of listening, even forgettable.

Using just the official Raspberry Pi powerpaks has sufficed for me. I suppose if I had spent thousands of dolllars on the downstream audio equipment I might be able to detect an improvement by substituting a well-designed linear power supply but then again I might not.

Remember that electrical noise is inherent in electronic systems and can affect i2S just as easily as USB interfaces. Some may leak in from the A/C mains; some may be generated in a switching power supply; some may be coupled between power, data, and clock traces on the printed circuit board or in interconnecting cabling; some is generated in the DAC circuitry itself. Good designers work to minimize the effect in their products through their choice of components and layout, through the network of traces on the circuit board, and through proper filtering. 

IMHO the present day products are light years ahead of what we had in the 60s - 70s when I was a first-time HiFi buff....at a fraction of the price. I have become immune to audiophila nervosa (you can look it up).

Regards,
Kent