How to avoid (rare) sound defects with USB DAC ?

[Benji]

Hello,

first warm congratulations for this excellent OS, very reactive, and delivering high quality sound with rather low cost hardware.

I bought the Pi 3 model B recently, and installed the last runeaudio version available for this.
I use an Audiophonics U-sabre TCXO Edition DAC plugged on an USB port of the Pi. Globally it works very well on most of my music on NAS, but I sometimes experiment little "pops" on some tracks, only with flac files, but it seems not correlated to the bitrate (= no issues with some > 1000kbps tracks, and sometimes issues 500-700 kbps tracks). It works flawlessly for webradios, and for Qobuz with airplay.

I read many times that USB DAC's could lead to small sound defects due to the management of ethernet/usb data by the same chip, but I also see that many people use USB DAC's with Pi, and that such configuration is not inadvisable on runeaudio site. I therefore wonder what to do :

1 - change buffer settings ? (current buffer size : 2048, 10% before play)
2 - use a dedicated power supply on the DAC ? (it is possible). However, I saw that max_usb_current is already set in the config file of the Pi, and I use an Aukru 5V/3A power supply for the Pi, therefore I doubt that the power delivered to the DAC is insufficient.
3 - Change a software parameter (config file ?), wait for future versions of runeaudio hoping it could eliminate the small defects ?
4 - Change to an integrated DAC in the Pi, like hifiberry etc. ? (I would prefer avoiding this solution)
5 - Other solution ?

Thanks in advance, and once again, congratulations for the excellent job !

Benjamin

[hondagx35]

[hondagx35]

[Benji]

Hi Frank,

thanks for your very quick answer, much appreciated. I managed to do both modifications (unbind DAC and modification of cmdline.txt) and I have the feeling it improved the situation (only very few "pops" remaining, noticeable on very few tracks such as classical lyrics - e.g. stabat mater by Pergolese). Still wondering how to totally eradicate the remaining pops. No chance with buffer settings, or DAC power supply ?

For the integrated DAC, there are 2 reasons why I would prefer avoiding this solution :
- the main : to keep using my USB DAC, also considering it was performing very well with tinysqueeze or daphile on a HTPC (but with noisy fans which led me to try RP),
- secondary reason, but possibly wrong : because I am wondering if integrated DAC's for RP will be as good as the USB one I bought at Audiophonics.

Anyway, I don't eliminate the possibility to use an integrated I2S DAC one day... but I wonder what to choose, to be sure not to be disappointed (hfiberry, I-Sabre TCXO, other ?...).

Thanks again,

Benjamin

[hondagx35]

[PeteB]

[hondagx35]

[PeteB]

Hey Frank,

and thanks for the comment. I have not tried the DAC+ Pro. I can also hack the DAC+ board in the same place where they put the zero-Ohm resistor, but I have not tried that either.

The immediate issue is that I do not feel I have a clean ground, or a single solid star ground, for a valid test. The DAC+ can make wonderful numbers if on a clean supply and isolated from the mains, (see yellow trace below, the first and second harmonic at -100db, noise at -110), but I cannot duplicate those results in a real use case, therefore I cannot demonstrate an improvement.



To demonstrate that a split supply is a real improvement in real life, I would first have to show the effect of the noise (the reduced SNR), and then I would have to show that the split supply is an improvement in the presence of the noise... at around -100 dba...

[dunghnguyen]

[hondagx35]

Hi dunghnguyen,

your USB DAC does not specifying any HID endpoint.
So there is nothing to unbind.

Also the tweaks i posted are for RP2 and RP3 with kernel 4.x and tested / mentioned for the 3.x kernel used on ODROID.

Frank