It should work not while Ardour is running. Ardour requires exclusive access to the soundcard.
Have you tried the other outputs? 3/4
Yes that’s correct. When Ardour is running nothing else produces any sound.
So I’m still no further on with this issue and I feel I’m so close to solving it!!! I can record into Ardour when my Audio/MIDI setup is using ALSA but I don’t get any playback. If I use Pulse Audio in my Audio/MIDI setup then I can get playback but can’t record!!!
Just to refresh I’m using Ardour 6.8 (downloaded and installed from the official website), a 2014 MacBook Pro with Linux Mint 20.2 and Cinnamon. All my other sounds applications work fine.
I’m also using Linux Mint 20.2/Cinnamon and never had any troubles with Ardour in years… So it should work… 
I’m guessing into the blue now, but do you maybe have system volume very low or muted, or done something else in Mint’s system sound menu? Using onboard sound card that would also prevent you from hearing Ardour…
Do you maybe use some effects on the master bus (the activity could in theory show sound prior hitting effects…?) or do you use Ardour’s monitor section…? Can you maybe post a screenshot of your master channel in the mixer view?
Here’s an interesting part
Playback Device 0 (CS4208 Analog):
Subdevice 0 (hw:PCH,0,0):
used by: pulseaudio (PID 1072)
access: MMAP_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
When Pulse uses the device it is 16 bit / stereo. While Ardour tries 32 bit and all channels.
That rings a bell. Some of those HDA/PCH soundcards are not correctly detected [1].
Assuming you have Ardour 6.8 from ardour.org, you can work around by starting Ardour like
ARDOUR_ALSA_DEBUG=768 Ardour6
(one line), then pick Audio System: ALSA. That will (256) use 16 bit + (512) force stereo.
If that works, we can make it permanent. If not let’s get more debug messages:
ARDOUR_ALSA_DEBUG=15 Ardour6
To fix the root problem (detect soundcard correctly), search the web for “options snd-hda-intel model=apple” – I have no first hand experience with that though.
Thanks and I’m encouraged by your view “So it should work”. Yes, I agree. It should. Trouble is it doesn’t. I’ve checked (many and several times) all of the parameters that might affect the sound output. System sound is fine (I guess you mean ALSAmixer settings) and the Mint system Sound is 100%.
I don’t have anything running on the master bus at all.
Hi Robin I tried what you suggested and got this (but still no sound)
richard@MacBook:~$ ARDOUR_ALSA_DEBUG=768 Ardour6
Ardour6.8.0 (built using 6.8 and GCC version 6.3.0 20170516)
Ardour: [INFO]: Your system is configured to limit Ardour to 1048576 open files
Ardour: [INFO]: Loading system configuration file /opt/Ardour-6.8.0/etc/system_config
Ardour: [INFO]: Loading user configuration file /home/richard/.config/ardour6/config
Ardour: [INFO]: CPU vendor: GenuineIntel
Ardour: [INFO]: AVX-capable processor
Ardour: [INFO]: AVX with FMA capable processor
Ardour: [INFO]: CPU brand: Intel(R) Core™ i7-4870HQ CPU @ 2.50GHz
Ardour: [INFO]: Using AVX and FMA optimized routines
Ardour: [INFO]: Loading plugin meta data file /opt/Ardour-6.8.0/share/plugin_metadata/plugin_tags
Cannot xinstall SIGPIPE error handler
Ardour: [INFO]: Loading default ui configuration file /opt/Ardour-6.8.0/etc/default_ui_config
Ardour: [INFO]: Loading user ui configuration file /home/richard/.config/ardour6/ui_config
Ardour: [INFO]: Loading 452 MIDI patches from /opt/Ardour-6.8.0/share/patchfiles
Ardour: [INFO]: Loading colour file /opt/Ardour-6.8.0/share/themes/dark-ardour.colors
Ardour: [INFO]: Loading ui configuration file /opt/Ardour-6.8.0/etc/clearlooks.rc
Ardour: [INFO]: Loading bindings from /opt/Ardour-6.8.0/etc/ardour.keys
Loading ui configuration file /opt/Ardour-6.8.0/etc/clearlooks.rc
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
ALSA: Cannot open device ‘hw:PCH,0’: Device or resource busy
Found nothing along /home/richard/.config/ardour6/templates:/opt/Ardour-6.8.0/share/templates
–[[ ALSA Device hw:PCH,0
playback
nchan : 2
fsamp : 44100
fsize : 1024
nfrag : 2
format : S16_LE
access : MMAP interleaved
capture
nchan : 2
fsamp : 44100
fsize : 1024
nfrag : 2
format : S16_LE
access : MMAP interleaved
synced
–]]
Scanning folders for bundled LV2s: /opt/Ardour-6.8.0/lib/LV2
Set cursor set to default
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
(ardour-6.8.0:10322): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 6 char 1: ‘colin.m.fletcher@googlemail.com’ is not a valid name: ‘@’
Butler drops pool trash
caught signal - shutting down.
Process is still running! trying SIGKILL
richard@MacBook:~$
Thanks for the screen shots - looking good for my judgement…
So Robin’s magic wisdom is the way to investigate further… 
Thanks Iaex. Just out of interest you use Ardour with Linux Mint without problems? I guess your are not using a MacBook Pro? I’m wondering if this is the fly in the ointment!!
Is this useful? Ardour playing back, no sound and the Sound settings in Preferences saying nothing is recording or playing!!
Still with Pulse Audio if I add another track the Pulse Audio volume control is registering my hand claps from the microphone but Ardour isn’t !!
That is OK - Ardour doesn’t show up as Application there (in ALSA mode)…!
Ardour does NOT allow to record via pulseaudio. This is intentional. Pulseaudio is not suitable for reliable pro-audio.
Ardour’s Pulseaudio support is only intended for rare cases when you e.g. want to listen to a mix in the train on the way home from the studio and don’t care about dropouts or artifacts or latency…
Yes, that is most likely the culprit here - as indicated by Robin… I’ve used several PC computers/laptops since (about) Linux Mint 18.x and Ardour 5.x and a professional USB sound card… So that is quite a different setup…
Do you have access to any other external soundcard…?
This looks good. It should work…
Also do use alsamixer. literally. It’s the low-level mixer terminal app. Your desktop’s “Sound” preference relates to pulseaudio only and has no bearing.
I am occasionally using a MacBook Pro, but it runs MacOS 
This applies to Mac OS not Linux. There is a related but more technically complex process for Linux, but based off what we have seen thus far this is not the issue I do not believe. If you were able to get BOTH Playback and no recording AND Recording and no Playback, but not both together, then we would look at this. As it is you haven’t gotten playback working which indicates a different problem.
SeabladeWhen starting Ardour the way like Robin has mentioned, have you set your master output to 1/2 instead of 3/4?