> Peter wrote: > I have to do a long term meeting of soundlevels. I use a > condenser microphone and a cheap soundmeter. > > My plan is frpm one speaker 1 meter from the microphones send > sine waves and place the sound meter beside the microphone. > Record the sound then adjust the line in level so the in-signal > is the same as measuered on the soundmeter. I'm a little bit confused. Audio is measured with decibels (dB). It does not matter if it is sound in the air (dB SPL, or Sound Pressure Level) or in a wire (dBu where 0 dB is 0.77 VRMS, disregarding impedance loading), or in a digital system (dB FS where 0 dB is the maximum encodable level) Once you have recorded a reference is should be just simple math. For example, if the SPL meter shows 80 dB SPL and your recording is at -15 dB FS, then 0 dB FS will equal 95 dB SPL. !!!! EXCEPT !!!! dB SPL measurements are a bit more complex. There is frequency filtering (A-weighted, C-weighted), and two time factors (fast, slow). This means that if your measured sound is different in frequency, or different in "crest factor" (average level compared to peak level) it _will_not_be_accurate_. > The results from the following measuremt will be 1 minute long > wav files and a plot from the file. > So : How do I compare data from recorded files and calculate the > correct decibel-levels.? Plot the recording with a dB scale, and add or subtract the values you calculated from the test recording. That is all. If you want average level, or peak level, or minimum level SoX can get that for you with stat or stats. > And why I not use a better sound-meter plugged in to the > computer, it is becasue they all have to bad range in frequenzy.. dB SPL is supposed to be frequency weighted. A-weighting and C-weighting have a different frequency response. That means that a dB SPL meter should NOT EVER have a flat frequency response. Despite all I wrote, I suggest you try it. If you are wanting approximate values, not "traceable, suitable for law work", the results will probably be just fine. If you want values that can be defended in a court of law, or deal with legal sound exposure limitations, it probably isn't going to be accurate enough, but it can still show approximate ranges. ------------------------------------------------------------------------------ Announcing the Oxford Dictionaries API! The API offers world-renowned dictionary content that is easy and intuitive to access. Sign up for an account today to start using our lexical data to power your apps and projects. Get started today and enter our developer competition. http://sdm.link/oxford _______________________________________________ Sox-users mailing list Sox-users@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/sox-users
