For a long time, we’re using continuous recording tools to record our radio broadcasts. Many of these tools were homemade and alsa-backup is the latest project of this “serie” (after jack-backup and just-record).
We bought a M-Audio Delta 66 last year to complete our multi-track captation system. We’re working for a long time with M-Audio sound cards and especially with Delta 44 ones. So we were a bit surprised when we discovered that the M-Audio Delta 66 revision E wasn’t supported by the alsa project.
To retransmit in live the Amparanoia’s gig at Esperanzah! festival, we need a additional 4 tracks sound card. On sunday, the challenge was to configure our Delta 66.
If you load the snd-usb-audio without option with the current (2.6.24) linux kernel, your Audiophile USB will send you a nice “noise”.
$ arecord -vvv -D hw:2,1 -c2 -t raw -r48000 -fS24_3BE /tmp/test.raw
Recording raw data '/tmp/test.raw' :
Signed 24 bit Big Endian in 3bytes, Rate 48000 Hz, Stereo
Hardware PCM card 2 'Audiophile USB (tm)' device 1 subdevice 0
Its setup is:
Max peak (12000 samples): 0x007ff202 #################### 99%
But if you take look, it isn’t a noise, it’s a swapped endian stream.
So we’ve just started a dedicated tool to perform long recordings : JustRecord. These few lines of python can record in loop via alsa, run as daemon, log with syslog and execute an external script when a file is ended, etc. Tiny but usefull And many features will follow.
For 4 years, Radio Esperanzah! capture about 30 hours of live each year for the Esperanzah! festival. Until the 2007 edition, we used various recorders (from Archos Gemini to Tascam Compact Flash recorder). But recording something like 20 concerts with a mobile device consumes a lot of time. Lives at Esperanzah! are performed sequentially on two stages. You need to plug and unplug everything 80 minutes and move the capture system to the other stage. It’s painful.
For this 2007 edition, we betted on a new system : install a computer on each stage for the whole festival. The idea is simple : each “satellite” records continuously and recorded files are retrieved periodically by our NAS server via wifi. No (or less) useless movement, the same setup installed for the three days of festival, no cable to plug/unplug, …
A great idea … but it required a lot of preparation. Here are some of the problems we had to solve.