EDIT: On recent Arch based Linux it works out of the box (Manjaro & Antergos): as of june 2017 at least

Just installed Ubuntu 14.04.3 LTS on an HP Spectre 360.

All worked great out of the box, except... the sound.

I changed the kernel version to 4.0.9-040009-generic (but I don't think it really helped). It works well anyway.

All forum posts talk about the Dell XPS 13, but they are not working for Spectre.

TL;DR:

The only solution can be found here in the GREY zone:

http://h30434.www3.hp.com/t5/Notebook-PC-Sound-and-Audio/HP-spectre-x360-on-linux/td-p/4980797

Yes, you must reboot 2 time! Weird.

EDIT

Below the essential part: --> It is all about kernel parameters in grub config

HOW TO:

Edit grub config by doing:

sudo vim /etc/default/grub

Edit the line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash'"

Replace it with:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor acpi_osi='!Windows 2013' acpi_osi='!Windows 2012'"

Then run:
sudo update-grub

Reboot TWO times. Yes. 2 times.

Then Sound works (FYI The sound card is now in HDA mode -not I2S).

To confirm, run: aplay -l
and make sure you have the following in the output:

card 1: PCH [HDA Intel PCH], device 0: ALC3242 Analog [ALC3242 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0

When you open the Alsa mixer (the ound mixer settings window), you should see a sound card displayed.

Note: The Added 'acpi_backlight=vendor' parameter apparently do nothing (it is supposed to keep backlight settings?)

EDIT BIS:

The card seems in mute mode as default. You need to setup pulseaudio correctly ( pulsaudio/Alsa ).

With Manjaro OpenRC Linux I had to add the following packages:

• pulsaudio


• pulseaudio-alsa


• pulseaudio-equalizer


• xfce4-pulseaudio-plugin


• xfce4-volumed-pulse

then start the pulseaudio server manually

pulseaudio --start

from (https://wiki.archlinux.org/index.php/PulseAudio#Starting_manually)

Now you can successfully launch the pulseaudio mixer (from associated the XFCE4 applet) & go to "output devices" and play with "port" and the sliders.