Low-CPU scheduled audio recording

Using readily-available freeware it's possible to use a windoze PC to make scheduled WAV recordings with very little CPU use.

Software requirements

See my software page for links to sources.

How it works

nnCron LITE is a clone of the Unix cron command, with negligible CPU or memory footprint and a task list in a standard, well-documented format which can easily be generated by, for example, a perl script, and edited by any text editor. Other schedulers which I tested used an inconvenient binary format.

cmd2wav is a command line utility by Brett Bartholomew which my tests showed was a lesser CPU hog by an order of magnitude than any of the graphical sound recorders which I tried.

It is relatively trivial to generate a crontab file which will start cli2wav at the required times, either by hand or using, for example, a perl script.

Example

This is a real-life example which used output from the Orbitron satellite tracking software

2006-08-10 22:43:51 RS-15 233.1 80.9 9.6 2123 336.2 -20.2

to generate crontab lines to record part of the satellite's pass. In this case the processing script set the recording to start 7 minutes before the expected TCA (allowing for summer time), recording for 10 minutes at 8kHz and 16 bits. It also adds a call to a program which forces the PC's monitor into standby mode to minimise RFI.

# turn off monitor 1 minute before recorder starts OK
# 35 23 8 10 * monoff4.exe
# start recording 7 minutes before TCA (2243utc, 80.9 deg)
# 36 23 8 10 * cmd2wav d:\rs15\rs15-%YY%%MM%%DD%%hh%%mm%.wav 600 16 1 8000

(This example does not record all of the satellite's pass.)

Document history