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Old 2 weeks ago
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tINY's Avatar
Originally Posted by grannis View Post
an admirable aim that appears to be going sideways already. Maybe it's worth elaborating scientifically on what you mean by non-linear?

In strict mathematical terms, no, IRs are not linear - but then not much is - only straight lines!

I'm pretty sure you don't mean that, but I'm not sure exactly what you do mean.

btw, computerised models (and I don't mean IRs specifically, which are relatively simple beasts in the modelling world) have no problem with non-linear modelling per-se, so again, if you can define what you mean better, we may get somewhere.

fwiw, whilst I do use a Helix and IRs, I always supplement it with a tube preamp which adds some - er non-linearity(*) that disguises the digital nature of the distortion.

What I mean by that, is that I hear digital distortion as too uniform - it's like it's been quantized at a very short tempo. The tube breaks up the pattern enough to my ears to sound a whole heap better.

Clearly I am not talking about speakers, so my analogy is not perfect to what you are trying to discuss, but I thought it might illustrate my point about needing to be more precise with the term non-linear.

The biggest issue in my mind is the IMD. When you have a non-linear system and apply more than a single sine tone, the output of the system (or speaker in this case) contains the sum and difference of the tones applied. The only standard test that I'm aware of is a two-tone IMD test. Since the different tones in a guitar signal are usually harmonically related, adding in Harmonic Distortion is usually a good substitute. It fools a lot of people and is probably good enough for most pop recordings.

Where there will be differences is when you start playing 3rds. Because of our modern even-tempered tuning, the harmonics of the 3rds are off by quite a bit.

When you have significant IMD, the harmonic series you get from a root-3rd chord is different than simple harmonic distortion. There are problems with all of the intervals, but the major 3rd is the most pronounced.