How to calculate the level of an "AUDIO IN" in dBA?

    Aug 14 2011 | 5:40 pm
    Just this. I would like to know how to calculate the level of an AUDIO IN in dBA. I would like to see the values in third octave 125hz - 20khz and graphically.
    Its possible??

    • Aug 15 2011 | 12:51 am
      to get A-weighting you need to filter the input using biquad with these arguments:
      {biquad~ 0.49735 0. -0.49735 -1.041289 0.109858]
      then get the rms value over 125ms
    • Aug 15 2011 | 10:13 am
      Terry how do you know the arguments of the biquad object?
      Is this the global value?? i would like to know the values in a multislider object like the screen of a sonometer.
      My object is create a sonometer.
      I have searched a sonometer patch but i haven't find.
    • Aug 16 2011 | 10:22 am
    • Aug 16 2011 | 11:46 am
      well I just derived them empirically-- you can test the coefficients yourself by plugging the values into filtergraph and see what sort of a curve you get. I did test the filter against a class-A spl meter to see how accurate it was and it seemed to be within less than 1 dB margin of error, which was adequate for my purposes at the time.
      as for the other question, you could design a set of cascading fft modules using pfft~, each of which only samples bins 4 to 6 of a different window-size (ie 4096, 2048 ......128, 64), one for each octave
    • Aug 16 2011 | 12:52 pm
      i think that i need to learn more. (^_^)
      but i dont know what is "af Tf Lu" from the patch.
    • Aug 16 2011 | 1:44 pm
      that code is about equal loudness, not A-weight which are completely different things, and it's also written in matlab, which I don't probably refers to amplitude (a) at corresponding frequency (f), but that's just a guess
      btw my previous post should read 'bins 3 to 5", not '4 to 6", if you want pseudo 1/3 octave analysis
    • Aug 16 2011 | 2:02 pm
      But if you use 40 fones you are on A-weight, isnt it?