CorOS Version: 2.0
Describe your issue:
I noticed a difference in sound going direct into my Amp or having the Quad Cortex in front.
So I measured SPL for different routings through the Quad Cortex vs direct:
Direct: -8.3 dB True Peak
Out 3: -7.1 dB True Peak; +1.2 dB vs direct
Send 1 as Out: -7.0 dB True Peak; +1.3 vs direct
Send 1 as Send Block: -4.7 dB True Peak; +3.6 dB vs direct
Send 1 as FX Loop Block: -2.4 dB True Peak; +5.9 dB vs direct
All connections were unbalanced instrument cables (TS) and I used pink noise. Input levels on the Quad Cortex were at about -9 dB, Input Level Trim at 0 dB, Impedance at 1MOhm, Type Instrument, Ground Lift Off. Volume Knob at 100 at all times.
With the same settings, using Room EQ Wizard and a calibrated soundcard, I also measured frequency responses. Out 3 (and also 4 I guess) has a more pronounced decrease at high and low frequencies. The response of the Send 1 Out was smoother:
Out 3: -2 dB at 10 Hz, -1.2 dB at 20 kHz
Send 1: -1.2 dB at 10 Hz, -0.3 dB at 20 kHz
That means you probably get a more clear sounding 4 Cable Method by using both Send Outs instead of Out 3 or 4 as shown in the manual. This was already discussed in a different thread.
While those differences may seem small, there definitely was a noticebale difference listening in front of my amp/cab. But that might be due to the level differences.
I also did a loudness analysis of the recorded pink noise and found that, interestingly, the peak to loudness ratio of the noise that passed through the QC had increased. That would mean not compression but some kind of expansion happened?
The loudness values:
Direct: -17.1 LUFS; Peak-to-Loudness 8.8 LU
Out 3: -17.7 LUFS; Peak-to-Loudness 10.5 LU
Send 1 as Out: -17.4 LUFS; Peak-to-Loudness 10.4 LU
Send 1 as Send Block: -15.1 LUFS; Peak-to-Loudness 10.4 LU
Send 1 as FX Loop Block: -12.9 LUFS; Peak-to-Loudness 10.4 LU
It looks like the first three measurements achieve about the same loudness, so maybe the outputs of the QC were actually matched to loudness levels by the designers. Since the Quad Cortex circuit somehow increases Peak-to-Loudness-Ratio that naturally results in slightly higher peak values through those outputs.
But why the Send Out has different levels whether it is used as Out, Send Block or Loop Block I do not understand nor do I think it should be that way. If the reason is electronics it should still be somehow levelled digitally in my opinion.
So without knowing anything about how and why this device works this way, I am left with some wishes/questions:
- When I run an empty preset just with some routing I want it to sound the same as when I plug directly into the amp. I see that that might not really be possible, since the QC is a piece of hardware in the end and has its own frequency response and impedance.
- I want Out 3 / 4 to sound the same as Send 1 / 2, because I don’t want to waste both FX Loops for the best sounding 4-Cable-Method. I again see how that might not be possible, since they seem to be wired differently electronically (maybe because the Out 3/4 are balanced?). But maybe this could be corrected digitally.
- I want Send 1 / 2 to have the same level, no matter if I put it as an Output, as a Send Block or as a Loop Block.