Mono sound from a USB sound card

ChimpsInTies

Please can someone help me because I've been at this all day and still not got it to work.

I've got a Pi3B running RetroPie
It's got a USB soundblaster 2 card.

I can get sound out of the USB card but it comes out in stereo and my cab only has one speaker in it which runs from a little mono amplifier. I seem to either get background menu music OR emulator sound but not both. Can anyone help me with the config so it works. I get the common mixer error people tend to get when using USB soundcards when a game is run:

"lv10: Volumecontrol Init() - failed to find mixer elements!"

if i do the following commands in console I get:

pi@retropie:~ $ cat /dev/urandom | aplay -D hw:1,0
aplay: main:788: audio open error: Device or resource busy

pi@retropie:~ $ pi@retropie:~ $ cat /dev/urandom | aplay -D hw:0,0
-bash: pi@retropie:~: command not found
ALSA lib pcm_hw.c:1713:(_snd_pcm_hw_open) Invalid value for card
aplay: main:788: audio open error: No such file or directory

pi@retropie:~ $ aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
card1
monocard
sysdefault:CARD=S2
    Sound Blaster Play! 2, USB Audio
    Default Audio Device
front:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    Front speakers
surround21:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    Direct sample mixing device
dsnoop:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    Direct sample snooping device
hw:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    Direct hardware device without any conversions
plughw:CARD=S2,DEV=0
    Sound Blaster Play! 2, USB Audio
    Hardware device with all software conversions

pi@retropie:~ $ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 1: S2 [Sound Blaster Play! 2], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

pi@retropie:~ $ amixer
Simple mixer control 'Speaker',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 52
  Mono:
  Front Left: Playback 32 [62%] [-20.00dB] [on]
  Front Right: Playback 32 [62%] [-20.00dB] [on]
Simple mixer control 'Mic',0
  Capabilities: cvolume cvolume-joined cswitch cswitch-joined
  Capture channels: Mono
  Limits: Capture 0 - 40
  Mono: Capture 20 [50%] [0.00dB] [on]

If I have anything in /etc/asound.conf like the below I don't get sound in when running my games.
/etc/asound.conf

pcm.card1 {
  type hw
  card 1
}

ctl.card1 {
  type hw
  card 1
}

pcm.monocard {
  slave.pcm card1
  slave.channels 2
#  type plug
  type route
  ttable {
    # Copy both input channels to output channel 0 (Left).
    0.0 0.5
    1.0 0.5
    # Send nothing to output channel 1 (Right).
    0.1 0
    1.1 0
  }
}

ctl.monocard {
  type hw
  card 1
}

pcm.!default monocard

In Emulation station if I got press Start | Sound Settings I have it set as
Audio Device: Speaker
OMX Player Audio: ALSA: hw:0,0

strangely, if I have nothing in etc/asound.conf I get sound in both games and in the menus but in the games it's stereo so I'm missing the right channel.

Please help me. It's driving me bonkers and I've read so much I think I'm going around in circles.

ChimpsInTies

Just in case anyone else comes across this I got it working. It wasn't easy and took some trial and error, there isn't very much documentation out there about the inner workings of the asound.conf file but I must have read it all.

The asound.conf file needs to look like this. Obviously if your usb sound card is a different number or you didn't disable the default sound output of the pi yours might be a little differnt bit this should mean you get no errors about mixers and both game sound and background music on ES play ok all through the left channel only.

pcm.custom {
  type plug
  slave
  {
    pcm "dmix:1,0"
  }
  ttable {
    # Copy both input channels to output channel 0 (Left).
    0.0 1
    1.0 1
    # Send nothing to output channel 1 (Right).
    0.1 0
    1.1 0
  }
}

ctl.custom {
  type hw
  card S2
}

pcm.!default pcm.custom
ctl.!default ctl.custom