Thursday, January 8, 2009


The main living room in our house has always been a little harsh to my ear; I've been complaining to the wife that there's just too many hard surfaces in the room (lots of windows) which make it very 'bright' acoustically. This has the big down sides of making it difficult to understand what people are saying on the other side of the room, and annoying the hell out of me which the kids start making a racket.

So when D poked me on the subject this evening, it motivated me to go measure the problem. Mostly in a half-arsed sort of way to start with.

I used a crappy USB webcam which happened to have an in-built microphone to record audio, and then a tiny bit of perl to play a 1 KHz pulse out of the TV speakers at reasonably high volume. (Just a single cycle of a 1 Khz sine wave).

There are so many things wrong with this as a measurement setup it's difficult to count them all (not a pure tone, speaker distortion, awful directional microphone, no calibration to speak of, etc, etc, etc) but it was to at least give me an indication that it was worth putting more effort into it.

The graph above is the result. X axis is in seconds. It's rather entertaining that there's still significant energy in echos at 250 ms past the impulse. So it's not just all in my head: The room really is very echoy. Which I already knew, but now I has some numbers! Which is surely most of the way to fixing the problem, right?

Unfortunately, reducing echo is probably going to be non-trivial. At least, it will be given that D's hard requirement is that I don't cover the windows in felt...

We'll start with simple things like throw rugs over the couches, a tablecloth over the dining table, felting the undersize of the table and the bench. And if all else fails, the dreaded curtains discussion will probably enter the stage.

But first I need to get a better microphone. And some sort of software that's able to effectively measure and display how much the echo has changed. And maybe a good psychoaccoustic model. And a pony!

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