measuring noise levels - help needed

["vickipowys" vpowys]

All,

Its spring in Australia, the birds are singing, but school holidays
have just started and kids on motor bikes are doing constant circuits
on the property next door.  One new 2-stroke bike is particularly
annoying.  There is a 1-minute recording of it on SoundCloud here:

http://snd.sc/VGh7DW

I would like to be able to get a rough estimate of its noise level
for legal reasons.  Does anyone know how I can estimate a decibel
reading from this recording?  Details of equipment are on SoundCloud.

My legal advice is that I have 'an entitlement to the quiet enjoyment
of my property' and that the 2-stroke motorbike noise constitutes 'a
legal nuisance'.

Being able to measure the actual noise level would be a bonus.

Thanks in advance,

Vicki Powys
Australia