Archive of the former Yahoo!Groups mailing list: MOTM

excuse my ignorance - why would i want to full wave rectify the
signal before inputting it to the lag processor?

Because, if you put an AC signal into a lag processor it will act like a low pass filter (sound familiar). If you put the signal through the lag processor with no lag time you will hear (pretty much) the original signal (as far as harmonic content). As you increase the lag time you will hear the filtering effect -- sounding much like changing the cutoff frequency of a low pass filter.

By using a full wave rectifier you are moving all the negative going portions of the waveform to the positive side of 0 volts -- you are flipping those sections into positive territory so if you listen to the output from the FWR you will hear a very different waveform than at the input (weird harmonic content) since the wave shape has changed radically.

By making the waveform fall only on one side of 0 volts we are adding (surprise) a DC component to the input signal (as well as screwing around with the harmonic content). If we use a lag processor to filter out the AC (since it acts like a low pass filter), we will be able to derive an envelope which follows the input signal.

Best,
John (but not the one who first mentioned FWR)