This week we'll continue exploring harmonic distortion.
Where is my mind?
As I explained in the previous installment, in the analog world, harmonic distortion is produced whenever a signal passes through any hardware device. Regardless of whether you follow the recommendations of the manufacturer in terms of level to get the best results or you don't even process the signal in any way, there will always be some distortion, even if minimal. To change the amount of distortion you only need to overload the input stage of the unit more or less to make it distort accordingly. The coloration induced depends on a lot of factors: whether it's a tube or solid-state unit, the quality of the components, etc. It would be useless to dwell on the subject, but we will however see how to distinguish better this coloration later on.
And how do you get the same result in the virtual world? I'll have to admit that, for a long time, the options in this regard were sort of a lousy consolation prize compared to the real analog world. However, this has changed in the last couple of years thanks to the increase of processing power, as well as the talent of some developers. This results in some modern plug-ins being able to replicate legendary hardware gear and even simulate quite convincingly harmonic distortion. And how do you control the amount of distortion? In the same way as you would in the "real world," namely overloading the input stage of the plug-in.
That's all very nice, but how do you assess the quality of the plug-in's harmonic distortion? That's indeed a thorny issue, considering that budding engineers have a hard time really grasping the phenomenon, which usually leads them to abuse it in detriment of the overall musicality. Fortunately, there's a method that will allow you to get familiar with the notion of harmonic distortion while highlighting the color provided by this or that plug-in!
Can you hear it?
To judge what a plug-in emulating an analog unit adds to any audio signal you only need to do the following: Start by duplicating the track you want to process. Now insert on one of these two tracks the plug-in you want to test. But don't process the signal at all! You are not trying to assess the processing itself (compression, EQ, etc.), what you want to analyze is the production of harmonic distortion. Now adjust the volume fader of each track so that they have identical loudness. Reverse the phase of one of the tracks and that's it! If you've done everything right you should be able to hear the harmonic distortion induced by the plug-in. You still can't quite grasp it? Raise the plug-in's input gain to increase the distortion, but don't forget to adjust the loudness so they are still equal.
This method has two advantages. First, it will help your ears learn to detect harmonic distortion. And, second, it allows you to distinguish better the coloration added by the plug-in. Isn't that nice?
In the next episode we'll see how to put in practice what you've learned today.