Best Audacity config for low freq recording project ?

I am working on a project where I want to record noise from an un-known source (neighbors ?). It is sudden, very short ( ~3 seconds ), loud enough to wake anyone up, and I believe is some sort of low frequency electronically generated noise.

I’ve tried using MP3 recorders that are apparently meant for recording lectures or dictation - they do not capture it at all.

I have a very limited range of equipment to use: A Focusrite Scarlett 2i2 USB audio interface, a single Sterling Audio ST51 condenser mic, and a laptop running Audacity 2.0.3 and Windows XP. I have the Audacity installed and have used it a few times.

I have no idea when the sound will occur other then between 11pm and 5am. I want to set up my system to continuously record, and later will examine the captured result.

I know how to spell audio - that’s about it. What would be the best setup of Audacity for this ?

If I want to save the recording, what file format would be best to retain as much of the original noise characteristics as possible ?

As a totally separate question … I’m wondering if there is any software available that I could setup to provide a logical trigger at the occurrence of a particular level of noise ? For example, at some point I might want to implement some action (turn on a lamp, activate a relay … something ???) after a particular noise is received. I’m a digital electronics engineer and would just need something sent out a serial or usb port as the trigger.

The Scarlett 2i2 came with Ableton Live Lite … would that have any advantages over Audacity ?

You can leave Audacity running with:
Audacity > Edit > Preferences > Recording > [X] Sound Activated Recording.

Every time there’s a sound over the threshold, Audacity will turn on and record it.

Audacity has no provision for Time Of Day metadata, so what you’re likely to get is all your noise instances smashed together into one show with no good way to tell when they occurred.

Audacity is a terrible Surveillance Recorder. See: No Time Of Day, and you can capture more work than the computer can handle, plus the computer can’t be doing anything else. No 4AM updates from Flash or Microsoft, and no Automatic Defragmentation. You’ll have to locate all that stuff and turn it off.

You may find that regular consumer grade microphones and amplifiers aren’t up to “Bump InThe Night” sounds. The internal normal noise in that equipment is frequently the same volume as the noises, making it very hard to manage. Your hearing is remarkably good at midnight.

There was another similar posting that dragged on for weeks. Our recommendation was to move.


You can record continuously.
But you don’t have to record at 44100 Hz if you only want to catch low frequencies.
Try 11025 Hz or less (project sample rate).

You can also tell Audacity to record in 16 bit format (Edit > Preferences > Quality) which will reduce the size of the recording.
A mono recording will be half the size of a stereo recording, so be sure to set the number of channels to “1 (mono)” in the device toolbar.

With the sample rate set to 11025 Hz (as suggested by Robert) and in 16 bit mono, you should have no problem recording 8 hours of audio, provided that you have enough space on your hard drive, but Audacity may be rather sluggish with such a long recording.