Latency doesn’t work with PulseAudio on linux

pulseaudio

I have two speakers. The first one is connected to a PCI card and the second one via Bluetooth. Sounds are played a little bit earlier on the PCI card so I want to add some latency. I downloaded the pulse audio GUI and I have this :

enter image description here

As you can see, I added offset of 2 seconds on the "Audio Interne" (the PCI card).

I checked with the command pactl list cards and I have this for the internal card :

Card #1
        Name: alsa_card.pci-0000_00_1b.0
        Driver: module-alsa-card.c
        Owner Module: 8
        Properties:
                alsa.card = "0"
                alsa.card_name = "HDA Intel PCH"
                alsa.long_card_name = "HDA Intel PCH at 0xf7f10000 irq 27"
                alsa.driver_name = "snd_hda_intel"
                device.bus_path = "pci-0000:00:1b.0"
                sysfs.path = "/devices/pci0000:00/0000:00:1b.0/sound/card0"
                device.bus = "pci"
                device.vendor.id = "8086"
                device.vendor.name = "Intel Corporation"
                device.product.id = "1e20"
                device.product.name = "7 Series/C216 Chipset Family High Definition Audio Controller"
                device.form_factor = "internal"
                device.string = "0"
                device.description = "Audio interne"
                module-udev-detect.discovered = "1"
                device.icon_name = "audio-card-pci"
        Profiles:
                input:analog-stereo: Entrée Stéréo analogique (sinks: 0, sources: 1, priority: 65, available: yes)
                output:analog-stereo: Sortie Stéréo analogique (sinks: 1, sources: 0, priority: 6500, available: yes)
                output:analog-stereo+input:analog-stereo: Duplex stéréo analogique (sinks: 1, sources: 1, priority: 6565, available: yes)
                output:analog-surround-21: Sortie Surround analogique 2.1 (sinks: 1, sources: 0, priority: 1300, available: yes)
                output:analog-surround-21+input:analog-stereo: Sortie Surround analogique 2.1 + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 1365, available: yes)
                output:analog-surround-40: Sortie Surround analogique 4.0 (sinks: 1, sources: 0, priority: 1200, available: yes)
                output:analog-surround-40+input:analog-stereo: Sortie Surround analogique 4.0 + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 1265, available: yes)
                output:analog-surround-41: Sortie Surround analogique 4.1 (sinks: 1, sources: 0, priority: 1300, available: yes)
                output:analog-surround-41+input:analog-stereo: Sortie Surround analogique 4.1 + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 1365, available: yes)
                output:analog-surround-50: Sortie Surround analogique 5.0 (sinks: 1, sources: 0, priority: 1200, available: yes)
                output:analog-surround-50+input:analog-stereo: Sortie Surround analogique 5.0 + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 1265, available: yes)
                output:analog-surround-51: Sortie Surround analogique 5.1 (sinks: 1, sources: 0, priority: 1300, available: yes)
                output:analog-surround-51+input:analog-stereo: Sortie Surround analogique 5.1 + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 1365, available: yes)
                output:iec958-stereo: Sortie Stéréo numérique (IEC958) (sinks: 1, sources: 0, priority: 5500, available: yes)
                output:iec958-stereo+input:analog-stereo: Sortie Stéréo numérique (IEC958) + Entrée Stéréo analogique (sinks: 1, sources: 1, priority: 5565, available: yes)
                off: Éteint (sinks: 0, sources: 0, priority: 0, available: yes)
        Active Profile: output:analog-stereo
        Ports:
                analog-input-front-mic: Microphone avant (priority: 8500, latency offset: 0 usec, available)
                        Properties:
                                device.icon_name = "audio-input-microphone"
                        Part of profile(s): input:analog-stereo, output:analog-stereo+input:analog-stereo, output:analog-surround-21+input:analog-stereo, output:analog-surround-40+input:analog-stereo, output:analog-surround-41+input:analo
g-stereo, output:analog-surround-50+input:analog-stereo, output:analog-surround-51+input:analog-stereo, output:iec958-stereo+input:analog-stereo
                analog-input-rear-mic: Microphone arrière (priority: 8200, latency offset: 0 usec, not available)
                        Properties:
                                device.icon_name = "audio-input-microphone"
                        Part of profile(s): input:analog-stereo, output:analog-stereo+input:analog-stereo, output:analog-surround-21+input:analog-stereo, output:analog-surround-40+input:analog-stereo, output:analog-surround-41+input:analo
g-stereo, output:analog-surround-50+input:analog-stereo, output:analog-surround-51+input:analog-stereo, output:iec958-stereo+input:analog-stereo
                analog-input-linein: Entrée ligne (priority: 8100, latency offset: 0 usec, available)
                        Part of profile(s): input:analog-stereo, output:analog-stereo+input:analog-stereo, output:analog-surround-21+input:analog-stereo, output:analog-surround-40+input:analog-stereo, output:analog-surround-41+input:analo
g-stereo, output:analog-surround-50+input:analog-stereo, output:analog-surround-51+input:analog-stereo, output:iec958-stereo+input:analog-stereo
                analog-output-lineout: Sortie ligne (priority: 9900, latency offset: 2000000 usec, available)
                        Part of profile(s): output:analog-stereo, output:analog-stereo+input:analog-stereo, output:analog-surround-21, output:analog-surround-21+input:analog-stereo, output:analog-surround-40, output:analog-surround-40+inp
ut:analog-stereo, output:analog-surround-41, output:analog-surround-41+input:analog-stereo, output:analog-surround-50, output:analog-surround-50+input:analog-stereo, output:analog-surround-51, output:analog-surround-51+input:analog-stereo
                analog-output-headphones: Casque audio (priority: 9000, latency offset: 2000000 usec, not available)
                        Properties:
                                device.icon_name = "audio-headphones"
                        Part of profile(s): output:analog-stereo, output:analog-stereo+input:analog-stereo
                iec958-stereo-output: Sortie numérique (S/PDIF) (priority: 0, latency offset: 0 usec)
                        Part of profile(s): output:iec958-stereo, output:iec958-stereo+input:analog-stereo

And I tried to do pactl play-sample bell.ogg alsa_output.pci-0000_00_1b.0.analog-stereo. It always seems instantaneous. The latency I set doesn't seems to change anything, even when I play music.

What can I do?

EDIT

With pactl list sinks, I see this :

Latency: 2039815 usec, configured 40000 usec

So it seems the latency is set correctly but it seems to be instantaneous when I play a sound. I suppose there should be a delay. Is there something I don't understand?

Best Answer

I guess the latency offset in your screenshot is just Pulsaudio calculating time to buffer sizes with given sample frequencies and trying to arrange this parameters with ALSA. Changing the latency offset there not showing an effect might just be an ALSA driver not supporting much variety in buffer sizes.

To get an extra buffer you could add a null sink to use module-loobpack's latency_msec like so:

pactl load-module module-null-sink sink_name=delayed
pactl load-module module-loopback latency_msec=2000 source=delayed.monitor sink=alsa_output.pci-0000_00_1b.0.analog-stereo

Then you have to combine the null sink with your bluetooth audio.

I've had the expected huge delay when testing this simple setup without module-combine-sink like this:

paplay someaudio.ext --device delayed
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