Telegram voice calls with JACK on FreeBSD 15 and a 24-channel USB interface (Soundcraft Signature 22 MTK)

dmitry n medvedev · Saturday at 10:07 AM

Environment

OS: FreeBSD 15
Audio server: JACK (OSS backend)
USB audio interface: Soundcraft Signature 22 MTK
The mixer exposes 24 USB capture channels.

The mixer is used as the primary audio interface, and all audio routing on the system is done through JACK.

The USB device therefore appears in JACK as:

Code:

system:capture_1
system:capture_2
...
system:capture_24

Signal path

Code:

microphone
   ↓
external processing (mic preamp / dbx processor)
   ↓
Soundcraft Signature 22 MTK
   ↓
USB multichannel audio (24 channels)
   ↓
JACK
   ↓
applications (OBS, Telegram, etc.)

Important channel mapping

In this setup:

system:capture_1 = microphone signal
systemlayback_21 and systemlayback_22 = USB return channels to the mixer

Application audio is returned to the mixer through PulseAudio:

Code:

PulseAudio JACK Sink:front-left  → system:playback_21
PulseAudio JACK Sink:front-right → system:playback_22

Observed problems

1. Telegram binary package

The Telegram package available for FreeBSD does not work correctly in this setup.

Telegram appears to expect a mono microphone device.

However the audio device exposed to applications has 24 capture channels, and Telegram does not correctly select the microphone channel.

2. PulseAudio JACK bridge

PulseAudio is currently used as a bridge between some applications and JACK.

The PulseAudio JACK source inherits the full number of channels from JACK:

24-channel input
22-channel output

As a result, Telegram sees a multichannel microphone device, not a mono microphone.

3. Attempt to rebuild Telegram with JACK support

An attempt was made to rebuild Telegram on FreeBSD so that it could use OpenAL Soft (alsoft) with JACK support, allowing Telegram to talk directly to JACK.

This build attempt failed and Telegram could not be successfully compiled with this configuration.

What I need

Conceptually I need something like this:

Code:

224-channel USB interface
        ↓
JACK routing
        ↓
virtual mono microphone device
        ↓
Telegram

In other words:

the microphone signal is system:capture_1
Telegram should receive only that channel as a mono input device

JACK routing

Output of:

 

jack_lsp -c

Code:

system:capture_1
   LSP Graphic Equalizer x32 Mono:in
   OBS Studio: mic:in_1
system:capture_2
system:capture_3
system:capture_4
system:capture_5
system:capture_6
system:capture_7
system:capture_8
system:capture_9
system:capture_10
system:capture_11
system:capture_12
system:capture_13
system:capture_14
system:capture_15
   OBS Studio: solo:in_1
system:capture_16
   OBS Studio: solo:in_2
system:capture_17
system:capture_18
system:capture_19
system:capture_20
system:capture_21
system:capture_22
system:capture_23
system:capture_24
system:playback_1
system:playback_2
system:playback_3
system:playback_4
system:playback_5
system:playback_6
system:playback_7
system:playback_8
system:playback_9
system:playback_10
system:playback_11
system:playback_12
system:playback_13
system:playback_14
system:playback_15
system:playback_16
system:playback_17
system:playback_18
system:playback_19
system:playback_20
system:playback_21
   PulseAudio JACK Sink:front-left
system:playback_22
   PulseAudio JACK Sink:front-right
PulseAudio JACK Sink:front-left
   system:playback_21
   OBS Studio: pa:in_1
PulseAudio JACK Sink:front-right
   system:playback_22
   OBS Studio: pa:in_2
PulseAudio JACK Sink:rear-left
PulseAudio JACK Sink:rear-right
PulseAudio JACK Sink:front-center
PulseAudio JACK Sink:lfe
PulseAudio JACK Sink:side-left
PulseAudio JACK Sink:side-right
PulseAudio JACK Sink:aux0
PulseAudio JACK Sink:aux1
PulseAudio JACK Sink:aux2
PulseAudio JACK Sink:aux3
PulseAudio JACK Sink:aux4
PulseAudio JACK Sink:aux5
PulseAudio JACK Sink:aux6
PulseAudio JACK Sink:aux7
PulseAudio JACK Sink:aux8
PulseAudio JACK Sink:aux9
PulseAudio JACK Sink:aux10
PulseAudio JACK Sink:aux11
PulseAudio JACK Sink:aux12
PulseAudio JACK Sink:aux13
PulseAudio JACK Source:front-left
PulseAudio JACK Source:front-right
PulseAudio JACK Source:rear-left
PulseAudio JACK Source:rear-right
PulseAudio JACK Source:front-center
PulseAudio JACK Source:lfe
PulseAudio JACK Source:side-left
PulseAudio JACK Source:side-right
PulseAudio JACK Source:aux0
PulseAudio JACK Source:aux1
PulseAudio JACK Source:aux2
PulseAudio JACK Source:aux3
PulseAudio JACK Source:aux4
PulseAudio JACK Source:aux5
PulseAudio JACK Source:aux6
PulseAudio JACK Source:aux7
PulseAudio JACK Source:aux8
PulseAudio JACK Source:aux9
PulseAudio JACK Source:aux10
PulseAudio JACK Source:aux11
PulseAudio JACK Source:aux12
PulseAudio JACK Source:aux13
PulseAudio JACK Source:aux14
PulseAudio JACK Source:aux15
LSP Graphic Equalizer x32 Mono:in
   system:capture_1
LSP Graphic Equalizer x32 Mono:out
OBS Studio: mic:in_1
   system:capture_1
OBS Studio: solo:in_1
   system:capture_15
OBS Studio: solo:in_2
   system:capture_16
OBS Studio: pa:in_1
   PulseAudio JACK Sink:front-left
OBS Studio: pa:in_2
   PulseAudio JACK Sink:front-right

PulseAudio configuration

 

pactl list short sinks

Code:

1  jack_out  module-jack-sink.c  float32le 22ch 48000Hz  IDLE

pactl list short sources

Code:

1 1  jack_out.monitor  module-jack-sink.c  float32le 22ch 48000Hz  IDLE<br>2  jack_in           module-jack-source.c float32le 24ch 48000Hz  IDLE<br>

Detailed PulseAudio sink information

 

pacmd list-sinks

Code:

1 sink(s) available.
  * index: 1
    name: <jack_out>
    driver: <module-jack-sink.c>
    flags: DECIBEL_VOLUME LATENCY
    state: IDLE
    suspend cause: (none)
    priority: 10000
    volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB,   rear-left: 65536 / 100% / 0.00 dB,   rear-right: 65536 / 100% / 0.00 dB,   front-center: 65536 / 100% / 0.00 dB,   lfe: 65536 / 100% / 0.00 dB,   side-left: 65536 / 100% / 0.00 dB,   side-right: 65536 / 100% / 0.00 dB,   aux0: 65536 / 100% / 0.00 dB,   aux1: 65536 / 100% / 0.00 dB,   aux2: 65536 / 100% / 0.00 dB,   aux3: 65536 / 100% / 0.00 dB,   aux4: 65536 / 100% / 0.00 dB,   aux5: 65536 / 100% / 0.00 dB,   aux6: 65536 / 100% / 0.00 dB,   aux7: 65536 / 100% / 0.00 dB,   aux8: 65536 / 100% / 0.00 dB,   aux9: 65536 / 100% / 0.00 dB,   aux10: 65536 / 100% / 0.00 dB,   aux11: 65536 / 100% / 0.00 dB,   aux12: 65536 / 100% / 0.00 dB,   aux13: 65536 / 100% / 0.00 dB
            balance 0.00
    base volume: 65536 / 100% / 0.00 dB
    volume steps: 65537
    muted: no
    current latency: 16.71 ms
    max request: 22 KiB
    max rewind: 0 KiB
    monitor source: 1
    sample spec: float32le 22ch 48000Hz
    channel map: front-left,front-right,rear-left,rear-right,front-center,lfe,side-left,side-right,aux0,aux1,aux2,aux3,aux4,aux5,aux6,aux7,aux8,aux9,aux10,aux11,aux12,aux13
    used by: 0
    linked by: 0
    fixed latency: 13.33 ms
    module: 17
    properties:
        device.api = "jack"
        device.description = "JACK sink (PulseAudio JACK Sink)"
        jack.client_name = "PulseAudio JACK Sink"
        device.icon_name = "audio-card"

Detailed PulseAudio source information

pacmd list-sources

Code:

2 source(s) available.
    index: 1
    name: <jack_out.monitor>
    driver: <module-jack-sink.c>
    flags: DECIBEL_VOLUME LATENCY
    state: IDLE
    suspend cause: (none)
    priority: 1000
    volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB,   rear-left: 65536 / 100% / 0.00 dB,   rear-right: 65536 / 100% / 0.00 dB,   front-center: 65536 / 100% / 0.00 dB,   lfe: 65536 / 100% / 0.00 dB,   side-left: 65536 / 100% / 0.00 dB,   side-right: 65536 / 100% / 0.00 dB,   aux0: 65536 / 100% / 0.00 dB,   aux1: 65536 / 100% / 0.00 dB,   aux2: 65536 / 100% / 0.00 dB,   aux3: 65536 / 100% / 0.00 dB,   aux4: 65536 / 100% / 0.00 dB,   aux5: 65536 / 100% / 0.00 dB,   aux6: 65536 / 100% / 0.00 dB,   aux7: 65536 / 100% / 0.00 dB,   aux8: 65536 / 100% / 0.00 dB,   aux9: 65536 / 100% / 0.00 dB,   aux10: 65536 / 100% / 0.00 dB,   aux11: 65536 / 100% / 0.00 dB,   aux12: 65536 / 100% / 0.00 dB,   aux13: 65536 / 100% / 0.00 dB
            balance 0.00
    base volume: 65536 / 100% / 0.00 dB
    volume steps: 65537
    muted: no
    current latency: 0.00 ms
    max rewind: 0 KiB
    sample spec: float32le 22ch 48000Hz
    channel map: front-left,front-right,rear-left,rear-right,front-center,lfe,side-left,side-right,aux0,aux1,aux2,aux3,aux4,aux5,aux6,aux7,aux8,aux9,aux10,aux11,aux12,aux13
    used by: 0
    linked by: 0
    fixed latency: 13.33 ms
    monitor_of: 1
    module: 17
    properties:
        device.description = "Monitor of JACK sink (PulseAudio JACK Sink)"
        device.class = "monitor"
        device.icon_name = "audio-input-microphone"
  * index: 2
    name: <jack_in>
    driver: <module-jack-source.c>
    flags: DECIBEL_VOLUME LATENCY
    state: IDLE
    suspend cause: (none)
    priority: 10000
    volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB,   rear-left: 65536 / 100% / 0.00 dB,   rear-right: 65536 / 100% / 0.00 dB,   front-center: 65536 / 100% / 0.00 dB,   lfe: 65536 / 100% / 0.00 dB,   side-left: 65536 / 100% / 0.00 dB,   side-right: 65536 / 100% / 0.00 dB,   aux0: 65536 / 100% / 0.00 dB,   aux1: 65536 / 100% / 0.00 dB,   aux2: 65536 / 100% / 0.00 dB,   aux3: 65536 / 100% / 0.00 dB,   aux4: 65536 / 100% / 0.00 dB,   aux5: 65536 / 100% / 0.00 dB,   aux6: 65536 / 100% / 0.00 dB,   aux7: 65536 / 100% / 0.00 dB,   aux8: 65536 / 100% / 0.00 dB,   aux9: 65536 / 100% / 0.00 dB,   aux10: 65536 / 100% / 0.00 dB,   aux11: 65536 / 100% / 0.00 dB,   aux12: 65536 / 100% / 0.00 dB,   aux13: 65536 / 100% / 0.00 dB,   aux14: 65536 / 100% / 0.00 dB,   aux15: 65536 / 100% / 0.00 dB
            balance 0.00
    base volume: 65536 / 100% / 0.00 dB
    volume steps: 65537
    muted: no
    current latency: 4.98 ms
    max rewind: 0 KiB
    sample spec: float32le 24ch 48000Hz
    channel map: front-left,front-right,rear-left,rear-right,front-center,lfe,side-left,side-right,aux0,aux1,aux2,aux3,aux4,aux5,aux6,aux7,aux8,aux9,aux10,aux11,aux12,aux13,aux14,aux15
    used by: 0
    linked by: 0
    fixed latency: 2.67 ms
    module: 18
    properties:
        device.api = "jack"
        device.description = "JACK source (PulseAudio JACK Source)"
        jack.client_name = "PulseAudio JACK Source"
        device.icon_name = "audio-input-microphone"

JACK configuration

Driver parameters:

jack_control dp

Code:

--- get driver parameters (type:isset:default:value)
                rate: Sample rate (uint:set:48000:48000)
              period: Frames per period (uint:set:1024:256)
            nperiods: Number of periods to prefill output buffer (uint:notset:1:1)
          wordlength: Word length (sint:set:16:32)
          inchannels: Capture channels (uint:notset:2:2)
         outchannels: Playback channels (uint:notset:2:2)
                excl: Exclusive and direct device access (bool:set:False:True)
             capture: Input device (str:notset:/dev/dsp:/dev/dsp)
            playback: Output device (str:notset:/dev/dsp:/dev/dsp)
              device: OSS device name (str:set:/dev/dsp:/dev/dsp4)
         ignorehwbuf: Ignore hardware period size (bool:notset:False:False)
       input-latency: Extra input latency (uint:notset:0:0)
      output-latency: Extra output latency (uint:notset:0:0)

Available drivers:

jack_control dl

Code:

--- drivers list
net
loopback
netone
dummy
proxy
oss

Engine parameters:

jack_control ep

Code:

--- get engine parameters (type:isset:default:value)
              driver: Driver to use (str:set:dummy:oss)
                name: Server name to use. (str:notset:default:default)
            realtime: Whether to use realtime mode. (bool:set:True:True)
   realtime-priority: Scheduler priority when running in realtime mode. (sint:notset:10:10)
           temporary: Exit once all clients have closed their connections. (bool:notset:False:False)
             verbose: Verbose mode. (bool:set:False:False)
      client-timeout: Client timeout limit in milliseconds. (sint:notset:0:0)
        clock-source: Clocksource type : c(ycle) | h(pet) | s(ystem). (uint:notset:0:0)
            port-max: Maximum number of ports. (uint:notset:2048:2048)
    replace-registry: Replace shared memory registry. (bool:notset:False:False)
                sync: Use server synchronous mode. (bool:set:False:False)
   self-connect-mode: Self connect mode. (char:notset: : )
       slave-drivers: Slave drivers to use (str:notset::)

Internal clients:

jack_control il

Code:

--- internals list
profiler
netmanager
netadapter
audioadapter

OSS / system audio configuration

/etc/sysctl.conf

Code:

hw.snd.default_unit=4

dev.pcm.4.bitperfect=1
dev.pcm.4.play.vchanrate=48000
dev.pcm.4.play.vchanformat=s16le:2.0
dev.pcm.4.play.vchanmode=fixed

hw.usb.uaudio.default_channels=24
hw.usb.uaudio.default_rate=48000
hw.usb.uaudio.default_bits=24

Question

How do FreeBSD users typically solve this situation when:

the audio interface exposes 24 capture channels
audio routing is handled by JACK
an application such as Telegram expects a mono microphone device

Possible approaches I am considering:

creating a virtual mono microphone device
JACK channel mixing
OSS virtual devices
PulseAudio remapped sources

What is the typical approach used in FreeBSD JACK setups for applications that expect a simple mono microphone device?

Tieks · 2026-03-09T19:39:20+0000

If you plug this device in, only pcm4 will be created? If so, what does cat /dev/sndstat tell you about pcm4?

Telegram voice calls with JACK on FreeBSD 15 and a 24-channel USB interface (Soundcraft Signature 22 MTK)

dmitry n medvedev

Environment​

Signal path​

Important channel mapping​

Observed problems​

1. Telegram binary package​

2. PulseAudio JACK bridge​

3. Attempt to rebuild Telegram with JACK support​

What I need​

JACK routing​

PulseAudio configuration​

​

Detailed PulseAudio sink information​

​

Detailed PulseAudio source information​

​

JACK configuration​

OSS / system audio configuration​

Question​

Tieks

Environment

Signal path

Important channel mapping

Observed problems

1. Telegram binary package

2. PulseAudio JACK bridge

3. Attempt to rebuild Telegram with JACK support

What I need

JACK routing

PulseAudio configuration

Detailed PulseAudio sink information

Detailed PulseAudio source information

JACK configuration

OSS / system audio configuration

Question