# https://www.runeaudio.com/forum/crossfeed-playback-for-more-realistic-headphone-audio-t2878.html#p9950

sudo apt-get install bs2b-ladspa


# This is what I add to /etc/mpd.conf
cat <<EOF | sudo tee -a /etc/mpd.conf >/dev/null
audio_output {
   type "alsa"
   name "ALSA default"
   device "hw:0,0"
   dsd_usb "yes"
}
#
audio_output {
   type "alsa"
   name "ALSA crossfeed"
   device "crossfeed"
   dsd_usb "yes"   
}
EOF


# And this is the /etc/asound.conf
cat <<EOF | sudo tee -a /etc/asound.conf >/dev/null
pcm.!default "crossfeed"
ctl.!default "crossfeed"

pcm.soundcard { type hw; card 0; device 0; }
pcm.plugSoundcard { type plug; slave.pcm "soundcard"; }

pcm.bs2b {
    type ladspa
    slave.pcm "plugSoundcard"
    path "/usr/lib/ladspa" #path under arch linux will be an other ?
    playback_plugins [ {
        label bs2b
   input {
   controls [650 9.5]
}   
} ]
}

pcm.crossfeed { type plug; slave.pcm "bs2b"; }
ctl.crossfeed { type hw; card 0; }
EOF

# 	parameters in "controls [x x]" can be changed.
# Here are some configurations of HZ and dB for Crossfeed:
# 	source: http://bs2b.sourceforge.net/

# These results shows a three versions with different sets of cut-off frequency 
# and crossfeed level:
# 	1) 700 Hz, 4.5 dB - default.
# 	This setting is closest to the virtual speaker placement with azimuth 30
#	degrees and the removal of about 3 meters, while listening by headphones.
# 	2) 700 Hz, 6 dB - most popular.
#	This setting is close to the parameters of a Chu Moy's [3] crossfeeder.
#	3) 650 Hz, 9.5 dB - making the smallest changes in the original signal 
# 	only for relaxing listening by headphones.
# This setting is close to the parameters of a crossfeeder implemented in Jan Meier's [4] CORDA amplifiers.

# Change of output is possible with:
# mpc disable 1
# mpc enable 2

# output of "aplay -L"

# null
#     Discard all samples (playback) or generate zero samples (capture)
# plugSoundcard
# bs2b
# crossfeed
# sysdefault:CARD=sndrpihifiberry
#     snd_rpi_hifiberry_dac,
#     Default Audio Device
# dmix:CARD=sndrpihifiberry,DEV=0
#     snd_rpi_hifiberry_dac,
#     Direct sample mixing device
# dsnoop:CARD=sndrpihifiberry,DEV=0
#     snd_rpi_hifiberry_dac,
#     Direct sample snooping device
# hw:CARD=sndrpihifiberry,DEV=0
#     snd_rpi_hifiberry_dac,
#     Direct hardware device without any conversions
# plughw:CARD=sndrpihifiberry,DEV=0
#     snd_rpi_hifiberry_dac,
#     Hardware device with all software conversions

# Interesting is "top":
# 	crossfeed disabled 12%
# 	crossfeed enabled 19%