Ok, understood, thanks for the explanation! My amixer says:
Simple mixer control 'PCM',0
...hence I used 'PCM' as mixer entry in settings.xml field 'scw_m', but I still cannot control the volume. Also, obviously the "auto detect" setting for 'playback route' (settings.xml field 'pcm_3') is not working reliably for my USB sound config (as you have already assumed), it only works from time to time, when I stop and restart Spotify app on my Android tablet.
Any idea which settings I can use for the settings fields 'pcm_3' (playback route) and 'scw_m' (mixer) given my USB device config (all details see below)? Many thanks for your help!
Here's is the lsusb output:
Bus 001 Device 004: ID 145f:0143 Trust
Here is the full amixer output:
Simple mixer control 'PCM',0
Capabilities: pvolume pvolume-joined pswitch pswitch-joined
Playback channels: Mono
Limits: Playback -10239 - 400
Mono: Playback -10239 [0%] [-99999.99dB] [off]
This is the dump of aplay -l:
**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
Subdevices: 8/8
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
Subdevice #2: subdevice #2
Subdevice #3: subdevice #3
Subdevice #4: subdevice #4
Subdevice #5: subdevice #5
Subdevice #6: subdevice #6
Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Device [USB Sound Device], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
Here is the dump of aplay -L:
null
Discard all samples (playback) or generate zero samples (capture)
default:CARD=ALSA
bcm2835 ALSA, bcm2835 ALSA
Default Audio Device
sysdefault:CARD=ALSA
bcm2835 ALSA, bcm2835 ALSA
Default Audio Device
default:CARD=Device
USB Sound Device, USB Audio
Default Audio Device
sysdefault:CARD=Device
USB Sound Device, USB Audio
Default Audio Device
front:CARD=Device,DEV=0
USB Sound Device, USB Audio
Front speakers
surround21:CARD=Device,DEV=0
USB Sound Device, USB Audio
2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=Device,DEV=0
USB Sound Device, USB Audio
4.0 Surround output to Front and Rear speakers
surround41:CARD=Device,DEV=0
USB Sound Device, USB Audio
4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Device,DEV=0
USB Sound Device, USB Audio
5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Device,DEV=0
USB Sound Device, USB Audio
5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Device,DEV=0
USB Sound Device, USB Audio
7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=Device,DEV=0
USB Sound Device, USB Audio
IEC958 (S/PDIF) Digital Audio Output
And finally this is my choosen Audio device config in LE:
ALSA: USB Sound Device (@:Card=Device,DEV=0), Analog
Again, many thanks for your help!
Cheers
Chunki