THD thought experiment - Adendum

So what do we know about THD measurements?

We know that if we take a regular sine wave, clip it and compare the measurements in the frequency domain we can see how much harmonic distortion there is.

So. If this is a valid way of measuring a distortion statistic, without looking at intermodulation; we should be able to clip two or more signals which ARE NOT frequency multiples of each other, and if THD is accurate we should see a generic harmonic pattern for each fundamental with no extra noise.

Below is an image of a signal before and after clipping, at 0.5. This signal had 3 components: 1kHz, 105Hz & 6318Hz.

As you can see, that hypothesis is totally incorrect. ‘But wait’, I heard you cry, ‘You are processing in the time domain and analysing in the frequency domain’.

Below is an example of the same thing, but I have clipped the signal in the frequency domain to the same level.

The difference is, we don’t amplify signals and pass them to loudspeaker drivers in the frequency domain.

We also don’t listen to stuff being played in the frequency domain, although that is the conversion our ears do.

If you clip something in the frequency domain, you aren’t changing the numerical pattern that is the signal. You are changing the level of the harmonic components within the signal.

If you clip something in the time domain, you are literally changing the number sequence, and thus modifying the harmonic content of the signal (the sequence is just the amalgamation of infinite sinewaves, right?) literally changes the frequency content of what you are hearing more than the magnitude of the frequency content. As such, if you used a nonlinear equation that changed the probability of number values to include an even distribution of +x over a given period, you effectively add more of a frequency pattern i.e. bass spectrum stuff.  I am talking about inverse-filtering in the time domain. Kind of similar to what a vacuum tube does by being nonlinear. Exciting.