I often have this problem with compressor pedals. This time with a Keeley Compressor Plus. My guitar outputs stronger signal than the Vpp limit of the compressor. So I need to turn down the volume knob to avoid the compressor start distorting. And it seems to work okay, but then you notice that at the highest positions (something like over the 20th fret) if you play note couples, the sound becomes strange, distorted. As if a third note would appear and it would create distortion. If you come lower to the 12th fret for example, and you play a couple, the guitar sounds clean. I checked the wave of the problem notes, and it looks to me there is no clipping. So overdriving may not be a problem. But then, why is this that those problem notes sound distorted?
To overcome the problem, what I need to do is that I turn the volume knob almost to the minimum on the guitar, then that distortion disappears from the highest notes, too. But then I need to compensate with gain at the end of my effect chain, that results in lots of noise appearing besides the signal.
I checked the problem in Spectralayers, and it can be seen, that when the problem notes ring, some kind of low end is added, that is lower than the fundamental of the lowest notes that I am picking. If I delete those parts, the sound is clean again. What is it that adds that noise? Some kind of flaw in the compressor circuit?
And what causes it? The signal passing the Vpp limit on the input, or something in the compression mechanism? I assume it is the former, because I have just analyzed the sample from a device (not compressor) where I sent a signal that I know was over the limit, and I can see a similar low end added, besides that I hear the distortion.
I dunno, I’m no expert…I just know what I hear and what I prefer
My fave demonstration is CycFi hex pickups in use. Yes, the demonstration in the video is using clipping. But, my goodness is the audio different
I’m gonna say IMD is just math and the more the signals get amplified, the more obvious the IMD effect. This is why power amplifier manufacturers are so aware and design to their best ability to tame IMD as much as possible.
Since then I managed to investigate that this problem is not caused by compressors. It is aleady in electric guitar signal, as least it is coming from the ones I have here. I managed to catch those additional notes. Every interval that you play around the 20-24th fret on my electric guitar has a 3rd note (every interval has a different one), that is usually lower than both of the notes in the intervals.
How could it be investigated where those additional notes are coming from? Maybe the signal get clipped in the potentiometer?
Intermodulation (the 3rd tone) can be ”evoked” when two signals with different frequencies travel simultaneously trough a non-linear system such as an amplifier. In linear systems it will not happen.
Our hearing itself is non-linear, the hair cells of our hearing organ (the cochlea) represent an active non-linear system. Thus we can perceive ”combination tones” and cochlear distorsion even if the signal itself (the two (sinus) tones in a given example) doesn’t contain any distorsion or even any harmonics.
This can be of special relevance if the interval between the two tones is a small one in the upper mids.
If you listen to a clean 1000 Hz sinus tone and a clean 1200 Hz sinus tone simultaneously and loud enough it’s quite possible to perceive a 200 Hz tone even though it’s not there physically. It’s a sort of biological intermodulation. Quite frustrating when it comes to mixing and mastering…
I’m not saying that this is the case for you but if the hearing is damaged on a cochlear level this phenomenon could be exaggerated and become more noticeable than it was without the damage.
My point is, it could be fruitless to look for active non-linear systems in a guitar.
and to further pile on to what we all already know:
no two people hear exactly the same thing (subjective condition)
that is why an objective system (for example the Spectrogram) is so helpful in aiding the subjective reference point
I’ll give a another example:
I have two Volvo motor vehicles. One of them (XC70) has a fairly accurate speedometer. By accurate I mean the speed displayed is nearly the correct actual speed. My XC90 SUV has a less accurate speedometer; displays about 3Kph less than actual speed. I wouldn’t know that without applying an objective device (GPS smartphone app) to test the speedometer accuracy.
So, in the case of this OP, more objective data may be required to attempt a solution. Whether the solution be a different amplifier or amplifier model or apply a filter or use a different guitar…or whatever to arrive at the result wanted. SLP can help figure that solution out, yet it may or may not be a condition of SLP software.
