apt get update missing release file [duplicate]

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