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

Hi Benjamin,

please try this:

- get accesss to the console
- determine your DAC USB address

dmesg |grep USB

You are looking for a line similar to:

[ 2.679233] input: HiFimeDIY Audio SA9023 USB Audio as /devices/platform/bcm2708_usb/usb1/1-1/1-1.3/1-1.3:1.0/input/input0

The only thing you need is 1-1.3:1.0 (your number may be different!!)

- Now unbind your DAC from USBHID

echo -n 1-1.3:1.0 > /sys/bus/usb/drivers/usbhid/unbind

- test it with different files

If this works, you can add this line to /var/www/command/orion_optimize.sh

##################
# common startup #
##################
#if [ "$PID" != null  ]; then 
#echo "Set priority for: cifsd"
#renice -20 $PID
#fi
cifsprio pid=$(pidof cifsd)
echo "Set normal priority for: rune_SY_wrk"
renice 20 $(pgrep rune_SY_wrk)
echo "Set normal priority for: rune_PL_wrk"
renice 20 $(pgrep rune_PL_wrk)
echo "Set normal priority for: smbd"
renice 19 $(pidof smbd)
echo "Set normal priority for: nmbd"
renice 19 $(pidof nmbd)

echo -n 1-1.3:1.0 > /sys/bus/usb/drivers/usbhid/unbind

You also can try to remove all dwc_otg.fiq* entries in /boot/cmdline.txt.

Frank

- Get access to the console:
Use SSH from your PC

If you are not familiar with SSH read this for Windows or this for Linux/MacOS
The default login for RuneAudio is "root" with the password "rune" (without quotes).

hondagx35

Hi Benjamin,

4 - Change to an integrated DAC in the Pi, like hifiberry etc. ? (I would prefer avoiding this solution)

Why?

I get the absolute best results with I2S DACs.
On my ODROID C1+ and C2 with Hifi shield i can play up to 32/384 without any clicks and pops.
Same on RP with Hifiberry, but limited to 192kHz.

All sound great!

Frank

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

Hi Benjamin,

Still wondering how to totally eradicate the remaining pops.

Sorry, but i'm out of ideas here.

Maybe someone else can help with this.

Frank

PeteB

@Benjamin:

I agree w. Frank about the I2S dacs, at least if you are on a budget like I am.

The main downside to the I2S hat DACs is the SNR is only as good as the power supply to the DAC.

Eliminating all pops, is very difficult, because there can be so many causes. I am down to very few, but there is no real difference between the type of DAC, once you eliminate the obvious. I have tested w. USB dacs, and I have a HifiBerry DAC+, and a DIGI+.

-A faster Pi (I tried a B+ at first, now a Pi2), this helped with less expensive USB dacs.
-A bigger buffer (I use 2x the default size, and 20%), this helped with higher bit rates over WiFi
-Forcing resample to 96K or lower (this seemed promising but only helped w older DACs that do not use USB async
-Relocating high bit-rate files to local flash drive, no more effective than increasing the buffer size, but more consistent

I would suggest that if you have a sample file that you can be sure exhibits the problem, try a bigger buffer or a local flash drive.

My theory is that as long as the data has to go through the Pi USB, there is no 100% effective solution, regardless of the USB having enough bandwidth.

hondagx35

Hi Pete,

The main downside to the I2S hat DACs is the SNR is only as good as the power supply to the DAC.

This also is valid for your USB DACs.

There are I2S DACs (e.g. Hifiberry DAC + pro) which offer the possibility to power the analog part from a separate power supply.

Frank

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

@[deleted]: my case, I dont see the number like you instructed. Could you advise me for this?
Thanks.

root@192.168.0.188's password:
===============  RuneOS distribution  ===============
  ____                      _             _ _
 |  _ \ _   _ _ __   ___   / \  _   _  __| (_) ___
 | |_) | | | | '_ \ / _ \ / _ \| | | |/ _` | |/ _ \
 |  _ <| |_| | | | |  __// ___ \ |_| | (_| | | (_) |
 |_| \_\\__,_|_| |_|\___/_/   \_\__,_|\__,_|_|\___/

================  www.runeaudio.com  ================
RuneOs: 0.4-alpha (build 20160516)
RuneUI: 1.3-alpha
Hw-env: ODROID-C2

root@runeaudio(ro):~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ODROIDHDMI [ODROID-HDMI], device 0: I2S.26 dit-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: x20 [xCORE USB Audio 2.0], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
root@runeaudio(ro):~# dmesg |grep USB
[    1.996906] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[    1.996980] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
[    1.997032] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters
[    1.997230] usbserial: USB Serial support registered for generic
[    1.998337] usbhid: USB HID core driver
[    2.046496] dwc_otg dwc2_b: new USB bus registered, assigned bus number 1
[    2.046970] hub 1-0:1.0: USB hub found
[    2.072017] dwc_otg dwc2_a: new USB bus registered, assigned bus number 2
[    2.072327] hub 2-0:1.0: USB hub found
[    2.481759] usb 1-1: new high-speed USB device number 2 using dwc_otg
[    2.743696] hub 1-1:1.0: USB hub found
[    3.022036] usb 1-1.1: new high-speed USB device number 3 using dwc_otg
[    3.202088] usb 1-1.2: new high-speed USB device number 4 using dwc_otg
[    3.324544] usb-storage 1-1.2:1.0: USB Mass Storage device detected
root@runeaudio(ro):~#

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

Benji

Hello,

just for information, I switched to wifi network connection instead of ethernet, and it seems it solved the issue, no more pops.

And up to now, no issue of bitrate on my side (but my tracks are 1000kbps maxi) - I saw that some people experimented some problems with very high bitrate tracks with the Pi3 native wifi.

Regards

Benjamin