JACK in Elphel cameras

This is example how using JACK on camera

- connect USB sound card to camera

- login via telnet and start jackd:

[root@Elphel353 /]# jackd -dalsa -dhw:0 -n3 -p512 -s -S

jackd 0.116.2
Copyright 2001-2005 Paul Davis and others.
jackd comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
JACK compiled with System V SHM support.
loading driver ..
creating alsa driver ... hw:0|hw:0|512|3|48000|0|0|nomon|swmeter|soft-mode|16bit
control device hw:0
configuring for 48000Hz, period = 512 frames (10.7 ms), buffer = 3 periods
ALSA: final selected sample format for capture: 16bit little-endian
ALSA: use 3 periods for capture
ALSA: final selected sample format for playback: 16bit little-endian
ALSA: use 3 periods for playback
playback and capture sample rates do not match (48000 vs. 24000) 

if You have different samplerate for capture/playback(as example, on my USB sound card) cancel jackd via ctrl-c and restart it via next command

[root@Elphel353 /]# jackd -dalsa -dplug:hw:0 -n3 -p512 -s -S

You can start JACK server in background as

jackd -dalsa -dplug:hw:0 -n3 -p512 -s -S 1>/dev/null &

Ok, now we can look avialable audio channels. (login another telnet session, session #2, if You not started jackd as foreground)

[root@Elphel353 /]# jack_lsp
system:capture_1
system:capture_2
system:playback_1
system:playback_2

For test output channels starting simple software metronom

[root@Elphel353 /]# jack_metro -b 120 &

Look at avialable channels:

[root@Elphel353 /]# jack_lsp
system:capture_1
system:capture_2
system:playback_1
system:playback_2
metro:120_bpm

Connect headphones to audio card. Now "connect" metronom output to playback channels of soundcard as

[root@Elphel353 /]# jack_connect metro:120_bpm system:playback_1
[root@Elphel353 /]# jack_connect metro:120_bpm system:playback_2

You can hear "beep" in headphones. Ok, disconnect metronom from output channels

[root@Elphel353 /]# jack_disconnect metro:120_bpm system:playback_1
[root@Elphel353 /]# jack_disconnect metro:120_bpm system:playback_2

For dump audio to wav files You can use utility timemachine

[root@Elphel353 /]# timemachine -c1 -t1 -p/var/tmp/hdd/tm -f wav -n dmpaudio 

where /var/tmp/hdd - path to directory where stored dump file

tm - prefix of file, filename look as "tm2009-09-27T05:08:44.wav"

dmpaudio - the JACK name timemachine will use

Connect, for example, metro:120_bpm to dmpaudio:in_1. Go to session #2 and enter

[root@Elphel353]# jack_connect metro:120_bpm dmpaudio:in_1
[root@Elphel353]# jack_lsp -c
system:capture_1
system:capture_2
system:playback_1
system:playback_2
metro:120_bpm
   dmpaudio:in_1
dmpaudio:in_1
   metro:120_bpm

Go to session where started timemachine and enter "start" waiting some time - enter "stop". Now You can play *.wav file and hear "beep"

Ok, disconnect metro:120_bpm from dmpaudio:in_1

[root@Elphel353]# jack_disconnect metro:120_bpm dmpaudio:in_1

and connect mic sound card to timemachine

[root@Elphel353]# jack_connect system:capture_1 dmpaudio:in_1

Go to session #1, enter command "start". Now You starting record from mic. Playing some time and stop record Enter command "stop". Trying play dumped wav file - You can hear sound from mic. You can mixing two or more sources to dump file - use jack_connect for it.

timemachine have next options:

Usage ./timemachine: [-h] [-i] [-c channels] [-n jack-name]                                             
       [-t buffer-length] [-p file prefix] [-f format]                                                 
       [-a] [-b begin-threshold] [-e end-threshold] [-T end-time]
       [port-name ...]
       -h      show this help
       -i      interactive mode (console instead of X11) also enabled
               if DISPLAY is unset
       -c      specify number of recording channels
       -n      specify the JACK name timemachine will use
       -t      specify the pre-recording buffer length
       -p      specify the saved file prefix, may include path
       -s      use safer characters in filename (windows compatibility)
       -f      specify the saved file format
       -a      enable automatic sound-triggered recording
       -b      specify threshold above which automatic recording will begin
       -e      specify threshold below which automatic recording will end
       -T      specify silence length before automatic recording ends
       channels must be in the range 1-8, default 2
       jack-name, default "TimeMachine"
       file-prefix, default "tm-"
       buffer-length, default 10 secs
       format, default 'w64', options: wav, w64
       begin-threshold, default -35.0 dB
       end-threshold, default -35.0 dB
       end-time, default 10 secs

You can start timemachine via options "-a" "-b" "-e" and record audio automaticaly