Detection of a specific sound

[John O'Hagan]

On Sun, 25 Oct 2015 17:17:28 -0700
Montana Burr <montana.burr at gmail.com> wrote:

> I'm looking for a library that will allow Python to listen for the
> shriek of a smoke alarm. Once it detects this shriek, it is to notify
> someone. Ideally, specificity can be adjusted for the user's
> environment. 

I've used python to detect and record ambient sound by launching
the simple command-line program sox (in its guise as "rec") as a python
subprocess. I hope someone corrects me, but the few python audio
libraries seemed to me to be overkill in terms of coding required and
underkill in terms of features. With sox, it's easy to set things like
length of recording and a triggering threshold etc.. The latter is good
for your use-case because you can set it high enough to only start
recording when something is loud enough to be an alarm. 

Once you have your recording, as others have pointed out, what you do to
detect an alarm sound in it will depend on what alarms sound like where
you live. 

> I'm thinking of recording a smoke alarm and having the program try to
> find the recorded sound in the stream from the microphone.

That kind of matching is IMO unlikely to work. The human ear (or
rather the brain's auditory processing) is very good at picking out the
same general sound in different contexts. Getting software to do this is
hard.

I had a quick look at the acoustid module, which uses Shazam-style
acoustic fingerprinting. It has a method for measuring the similarity
of different recordings, but my little trials weren't promising. A test
recording of my ringtone measured as identical to itself (so far so
good), but only about 25% identical to another recording of the same
ringtone. A recording of me randomly whistling also measured about 25%
similar to the ringtones. 

If your smoke alarms are anything like mine, they have a fixed pitch,
volume and pulse, simple machine-friendly properties that are unlikely
to happen by accident. You could try the aubio module (not a typo,
that's aubio with a "b"). I've never used it and it's python 2 only,
but it has pitch, onset time and "beat" detection. You might be able to
use it to measure those properties from a sample recording, and then
check your monitored recordings to see if they have roughly the same
measurements.

Regards

John