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sound_optimizations.md

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Sound Optimation for Raspberry PI based audio players

Based on Linux Audio Adjustments

  • added in /boot/cmdline.txt: isolcpus=2,3

    console=tty1 root=PARTUUID=4dce75b8-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles isolcpus=2,3

  • changed options in /lib/systemd/system/mpd.service

    CPUSchedulingPolicy=fifo
CPUSchedulingPriority=70
Nice=-15
ExecStart=/usr/bin/taskset -c 2,3 /usr/local/bin/mpd --no-daemon $MPDCONF

  • /etc/sysctl.conf

    net.core.rmem_max = 16777216
net.core.wmem_max = 16777216

  • /etc/security/limits.conf

    audio - rtprio 99
@audio - memlock 512000
@audio - nice -20

  • Run /home/pi/bin/optimize_sound at boot

    #!/bin/sh
#Reduce Audio thread latency
chrt -f -p 54 $(pgrep ksoftirqd/0)
chrt -f -p 54 $(pgrep ksoftirqd/1)
chrt -f -p 54 $(pgrep ksoftirqd/2)
chrt -f -p 54 $(pgrep ksoftirqd/3)

#Uncomment for MPD Affinity and Priority
#chrt -f -p 81 $(pidof mpd)
#taskset -c -p 2,3 $(pidof mpd)

#USB Dacs Uncomment to reduce USB latency
#modprobe snd-usb-audio nrpacks=1

#SPDIF HAT and WiFi users Uncomment to turn off power to [Ethernet and USB] ports
#echo 0x0 > /sys/devices/platform/soc/3f980000.usb/buspower

#Reduce operating system latency
echo noop > /sys/block/mmcblk0/queue/scheduler
echo 1000000 > /proc/sys/kernel/sched_latency_ns
echo 100000 > /proc/sys/kernel/sched_min_granularity_ns
echo 25000 > /proc/sys/kernel/sched_wakeup_granularity_ns

  • Create /usr/lib/systemd/system/sound.service

    [Unit]
Description=Sound

[Service]
ExecStart=/home/pi/bin/optimize_sound

[Install]
WantedBy=multi-user.target

  • Reording ALSA devices by creating /etc/modprobe.d/alsa-base.conf

    Refer to this Document

    Let us say you have two cards (snd_soc_allo_piano_dac_plus on I2C an another DAC on usb) and we want the I2C audio card to appear first followed by the USB DAC.

    cat /proc/asound/modules
0 vc4
1 vc4
2 snd_usb_audio
3 snd_soc_allo_piano_dac_plus

    Now you need to create /etc/modprobe.d/alsa-base.conf like this

    options snd_soc_allo_piano_dac_plus index=0
options snd_usb_audio index=1
options vc4 index=2
options snd slots=snd_soc_allo_piano_dac_plus,snd_usb_audio,vc4