rocklander wroteagain, thanks PeteB.. I'm pretty sure I have a ferrite ring about the place here (unless I've been asked to 'tidy' it by my missus), so will look for that.. there certainly appears to be enough current supply from the UI series so far.
I guess the next (n00b) question is around DACs.. recommendations? bang for buck? does it matter? I suppose there's already multiple threads on them here, but seems apt to ask in the PI3 thread since that's what I have.. (in case there's any difference between different PI units.. I'm seriously well beyond my comfort zone on this stuff..week 3 and all that).
Hi Rocklander!
I have a Suptronics x400 DAC which is a pi Hat. It doesn't operate via the USB at all and instead goes via the i2s interconnect via the GPIO pins. What made me buy it was a) a really really high spec DAC, b) price and c) it can take a voltage source from 6-24v and regulate it to a nice, smooth 2.5a @ 5v, and feed it to the pi (via the gpio pins too!). I'm in the process of designing a rune audio based hifi complete with cd playback, an analogue RCA input, and possibly DAB+ Digital Radio/FM Radio (very difficult so far). I know that hiss you're talking about, and even with a pristine dac, great power in and an i2s interconnect, there is always a little bit of digital noise at the extreme lows of any recording, unless they have been stripped out during the mastering process. In this case, the file you're playing through is most likely the issue, and you'd need to find some 24kbit FLAC files to really test that theory out, and even then they would have be a good recording. Put short, theres no such thing as perfect in either analogue or digital worlds, but this is probably the best you'll get type of scenario.
Heres a pic of my pi and hat, sitting on top of the speakers the hat powers -
Going via the i2s interconnect means that the signal path of the audio from the cpu is not only isolated from the USB bus, but is also sent with its own clock. Technically speaking, this means the timing mechanism that lets the receiving device know what speed to play the file, is separated from the audio stream itself, rather than piggybacked upon the same digital signal. This is what attracted me to the pi as an audio solution over other more powerful boards. USB DACs also often have internal wiring that separates the clock from the audio, but they still have to go via the singular USB bus built into the pi, which depending on your application, may already be at its very limited data threshold.
Also, the very act of digitizing an analogue source and converting it to digital is in itself lossy, regardless of the file format, bitrate or the frequency however there gets to a point where the human ear can't tell the difference, for most people they can't tell but anyone with a good ear (like yourself) can. Its for that reason we generally go above and beyond the efforts of most people, simply because we care 😉
Hope this helps
-D
