Today I am going to explore the intricacies of a few different types of distortion; Clip distortion, gain distortion and room distortion. Firstly I will examine clip distortion.
To test this I primarily worked in the box using Logic X as my DAW. I ran a signal generator running a 1Khz sine wave and boosted the gain. I then printed it onto an audio track on another channel. Here is the frequency analyser showing the regular sine wave first.
As you can see it is just the singular frequency showing. When the signal is boosted to an ungainly(heh) level the frequency analyser shows something a little different.
Looking at this analyser you can see all the upper harmonic content that the clipped signal has added. Here is a look at the waveform comparing a sine wave to the clipped, now a square wave signal.
Clip distortion is an easy thing to encounter but also an easy thing to fix. By lowering your input volume into the DAW you will avoid clip distortion. That being said there could very well be instances where the clipping adds something extra to the sound you are recording and may be a desired effect.
The next form of distortion I am going to look at will be the room distortion. Now I am not too sure if this is classified as a type of distortion but I wanted to show the effect that a room can have on a sound.
To test this I ran a signal generator putting out 1Khz through my monitors at home and recorded it with my little 12 gauge shotgun shell microphone. Here is the sound and the analyser screenshot.
Comparing this to the clean in the box sine wave you can see the small amount of lower end content that wasn’t there. Overall it sounds pretty good, it’s a sine wave no worries. To express the distortion a little more obviously I ran an EQ to cut 1Khz and boost everything else. Have a look here.
Boosted Recorded Sine (sorry about the clippy bit at the beginning, Logic is weird sometimes?)
You can really see the extra distortion content that is added from the room (and probably mic choice). Interesting to note that the sine has peaks at 2Khz and 3Khz, showing the logarithmic nature of sound. It probably says something about my room too but I am not learned enough yet to explain in full.
Now my interface is a little old and because of that some of the pots are a little scratchy. I ran the same test as before but turned the gain up slowly to capture the rasp of the pot.
Now because the distortion only happens when the pot is moving, I took this screenshot at the point where the level is being boosted. You can easily see all the extra unwanted harmonics that an old scratchy gain pot can add to your tone. I also did the same eq boost and cut as I did above. It is unnecessary as the distortion is obvious but here it is anyway.
Lastly regarding this scratchy pot distortion you can examine the waveform and easily see that the waveform changes shape as the pot moves to increase gain.
The most obvious way to avoid this kind of distortion is to not move your pots, but that is just not possible in many cases. There are products available that can aid in the removal of the scratchy pot, namely DeoxIT.
To test gain distortion we decided to not use a sine wave but instead a snare drum. We took a normal take at an appropriate level first and then we boosted the gain much higher to achieve some distortion. We used the AKGC414 microphone set on cardioid polar pattern close mic’d to the edge of the snares batter head. Unfortunately I did not take a photograph of the set up. This is essentially the set up but without the overheads and on a snare drum.
Here is the normal snare sound played by the ever rhythmic Jeff McKenner.
It follows a pretty standard shape for a snare drum hit. With a fundamental frequency of ~220Hz it is a fairly normal snare sound. Now if we have a look at the high gain snare drum we can see a big difference.
There is a lot of extraneous frequencies here. With a big boost in the low-end and significant rise in the mid to high end you can really obviously hear the difference. It almost sounds as if there has been a reverb applied after the fact (no I did not put a reverb on the snare). The sound has its merits though, and is not completely horrible and unusable. The obvious way to avoid this is to just turn down the gain on the pre-amp or interface.
There are quite a few forms of distortion in regards to the audio world but most of them are easy to combat with some being much more difficult than others. Things such as clip or gain distortion are a simple fix with turning down your input level being the solution. That being said there could be times where the distortion, while being destructive, is destructive in a useful manner and should be investigated as to whether there is worth in the sound. Distortion such as the kind you get with a bad room is much more difficult to eradicate and can become quite expensive. The solution to an inappropriate recording room is not as clear-cut as it is with the other kinds of distortion. You can go so far as to decouple the room from the exterior space and have it “floating” to reduce unwanted room sound. The bottom line is that distortion is and always will be a part of audio, but the more you know about it the easier it is to combat and harness to your own ends.
Resources(Google Drive) – Audio and Images. Poorly organised Logic X session.
LO Coverage will hopefully be 2, 16 and 21