I think I may have found a possible issue with my Quad Cortex Mini - version 4.1.0 f9381db.
When I use a high-gain preset, if I let the three highest strings — G, B and high E — ring open and then play the low E string, the low E suddenly loses a large amount of gain and sounds much cleaner/thinner.
As soon as I mute the three high strings, the low E immediately gets its normal gain back.
So far, I have tested:
Noise Reduction completely disabled
Input Gain at 0 dB
Different gain levels on the amp
Different high-gain amp models
Two different guitars
A very simple signal chain: Input → Amp → Cab → Output
The problem happens in all of these cases.
It does not seem to be related to a specific guitar, amp model, or Noise Reduction setting.
Has anyone experienced something similar? Could this be related to the input stage, processing, or some kind of intermodulation/compression behavior?
I can also provide a video showing the issue if that helps.
That sounds like a useful reproducible case, especially since muting the open strings restores the low-E level immediately. I’d try one more controlled comparison: record the same picking sequence into a looper or DAW, then feed it back at a fixed level (if you have a clean DI available). Watch the input meter and, if possible, any amp input/output meters while comparing open G-B-E versus fretted notes at the same pitches. Also try lowering the guitar volume a little and changing the input impedance or input mode, if the Mini exposes those options. If the drop follows the summed signal rather than the physical strings, the recording plus the exact preset export would give support a much cleaner DSP repro than a video alone. It may also be worth noting whether the drop appears before the amp block or only after it.
Thank you for your help. I contacted support, and they sent me the response below:
Response:
What you are describing is expected behaviour with high-gain amplification rather than a fault with the Quad CortexMini.
The amp processes the combined signal from all six strings, not each string independently. When the open G, B, and high E strings are already ringing, their combined signal drives the amp’s nonlinear compression and distortion. Playing the low E then changes the overall waveform and creates harmonic masking and intermodulation, which can make the low note sound thinner or less saturated.
Once the higher strings are muted, the low E becomes the dominant signal again, so its full gain and harmonic content become more apparent. This also occurs with physical high-gain amplifiers and is unrelated to the Noise Reduction setting.
Should you require any further clarification or assistance, please do not hesitate to let us know.
