16.04 - apt get update missing release file

After doing apt-get-update I always get these error messages:

Reading package lists... Done
W: The repository 'http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
N: Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'http://dl.google.com/linux/chrome/deb stable InRelease' doesn't support architecture 'i386'
E: Failed to fetch http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

I read a post saying the contents of /etc/apt/sources.list (see below) should be changed. Which lines need commenting out?

# deb cdrom:[Ubuntu 11.10 _Oneiric Ocelot_ - Release i386 (20111012)]/ oneiric main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://gb.archive.ubuntu.com/ubuntu/ xenial main restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://gb.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://gb.archive.ubuntu.com/ubuntu/ xenial universe
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial universe
deb http://gb.archive.ubuntu.com/ubuntu/ xenial-updates universe
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://gb.archive.ubuntu.com/ubuntu/ xenial multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://gb.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://gb.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu xenial-security main restricted
deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
deb http://security.ubuntu.com/ubuntu xenial-security universe
deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
```

EDIT:
contents of sources.list.d:

brightbox-ruby-ng-trusty.list
brightbox-ruby-ng-trusty.list.save
danielrichter2007-grub-customizer-precise.list
danielrichter2007-grub-customizer-precise.list.distUpgrade
danielrichter2007-grub-customizer-precise.list.save
google-chrome.list
google-chrome.list.distUpgrade
google-chrome.list.save
heroku.list
heyarje-libav-11-trusty.list
inkscape_dev-stable-trusty.list
inkscape_dev-stable-trusty.list.save
maarten-baert-simplescreenrecorder-trusty.list
maarten-baert-simplescreenrecorder-trusty.list.save
megasync.list
megasync.list.distUpgrade
megasync.list.save
ondrej-php-trusty.list
ondrej-php-trusty.list.save
oneiric-partner.list
oneiric-partner.list.distUpgrade
oneiric-partner.list.save
spring-ppa-trusty.list
spring-ppa-trusty.list.save
thomas_tsai-ubuntu-tuxboot-trusty.list
thomas_tsai-ubuntu-tuxboot-trusty.list.save
webupd8team-java-trusty.list
webupd8team-java-trusty.list.save

I have tested the ppa by adding them, it's also show same error you occurred:

W: The repository 'http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found

If you go to their launchpad ppa page, you'll see the ppa no longer available as 13.10 (Saucy Salamander), which cause 404 Not Found error:

In order to get rid of error, simply removing the ppa:

sudo add-apt-repository --remove ppa:ubuntu-audio-dev/ppa
sudo apt-get update
sudo apt-key del 72B194E5

Update

For There is no public key available error, run following on terminal:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 1397BC53640DB551

For google chrome in Release file error, do following steps:

1. Open a new Terminal window and run the following command:

   
   

   sudo gedit /etc/apt/sources.list.d/google-chrome.list
   




2. In the text file that opens edit the file so that the line reads:

   
   

   deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main
   




3. Hit Save. Close the Gedit window.

_Source