Help - ~15dB of noise added by using FX loop (in/out4) (solved)

[fuzzyoctaves]

I turned off the gates in my signal and realized that the Out4/In4 loop is adding ~15dB of noise. I tested this by simply putting a single cable between the two and then switching between routing through and around.

I am only using the Left signal path for mono, so Out4Left to In4Left.

Settings in I/O:

Input 4 Source = Analog
Input 4 Mode = Left Only

Output 4 Configuration:
Mode = Copy L->R
Boost/Pad = 0 dB (interestingly, the noise goes down as I increase this, but even at the max of 18dB, there is still ~8dB of noise added)
Phase = Normal
Copy Input 1 = Off

A/D Sensitivity Input 4 = 50% (the noise increases significantly as I lower below 50%)

All Global EQ settings for Out 4 are at 0.00dB

What am I missing?

 

[unix-guy]

Try another cable?

 

[fuzzyoctaves]

Try another cable?

Did that - same results. I even removed the cable and there is still an additional ~5dB of noise by just having IN/Out4 in the signal path

 

[mr_fender]

Adjust your Input 4 Input Sensitivity for the best signal to noise ratio. Turn it up as high as you can without clipping. Do the same with the Output 4 Boost/Pad. Those will help a lot. You could try a humbuster cable on Output 4 too. Some small amount of additional noise is inevitable since you're adding more analog stuff to the signal path, but adjusting for the best SNR should help.

 

[fuzzyoctaves]

Adjust your Input 4 Input Sensitivity for the best signal to noise ratio. Turn it up as high as you can without clipping. Do the same with the Output 4 Boost/Pad. Those will help a lot. You could try a humbuster cable on Output 4 too. Some small amount of additional noise is inevitable since you're adding more analog stuff to the signal path, but adjusting for the best SNR should help.

Adjusting the A/D Sensitivity for Input1 from 50% - 100% reduces maybe 1dB of this loud noise.

I get ~30% of this noise without a cable from Out4 to In4... Interestingly, going from 50%-100% on A/D Sensitivity without the cable does make a perceptible difference. This takes the noise down to ~3.5dB - still really loud.

 

[FractalAudio]

D/A followed by A/D will add 6dB of noise. Add in some analog electronics and you usually can expect about 8-10dB of SNR degradation.

See the manual for the correct way to set up a unity-gain loop.

 

[mr_fender]

So you're getting added noise by just putting the OUT 4 and IN 4 blocks in the chain with no cable between their jacks? That doesn't seem normal. With no cable connected to Input 4, the signal should be grounded and silent. What does your grid routing look like?

 

[fuzzyoctaves]

See the manual for the correct way to set up a unity-gain loop.

I have done a full RTFM and will add:

1. I already had Out4 Level turned full clockwise.
2. I have adjusted the A/D Sensitivity to 85% (I am hitting red on the output meter occasionally at this setting, but I don't get a clip indicator)
3. I haven't tried a humbuster cable yet, but there is still ~3dB more than when I route around Out4/In4 with the cable pulled

With this, I am getting ~14dB of noise with a cable between Out4 > In4, with the cable pulled, it is ~5dB.

 

[fuzzyoctaves]

So you're getting added noise by just putting the OUT 4 and IN 4 blocks in the chain with no cable between their jacks? That doesn't seem normal. With no cable connected to Input 4, the signal should be grounded and silent. What does your grid routing look like?

I made a simple patch to test it out. Using the M-Plex to switch In/Out4 in and out of the signal path

 

[FractalAudio]

View attachment 144398


I made a simple patch to test it out. Using the M-Plex to switch In/Out4 in and out of the signal path

You've added an extra A/D conversion. That will add noise. It's physics.

 

[mr_fender]

Ah, your loop is before the amp. The compression of the amp and drive blocks is likely making the noise difference much more noticeable.

 

[mr_fender]

No need for a multiplexer block for that test either. Just connect the Out 4 and In 4 blocks together on the grid and Bypass the In 4 block to bypass the loop. When an In block is active it's fed by its associated jacks. When it's bypassed, it's fed by its input on the grid.

 

[fuzzyoctaves]

You've added an extra A/D conversion. That will add noise. It's physics.

Got it. I just wanted to make sure I hadn't made an error somewhere. I'll take note of the details and work around. As always, deep appreciation for all the things.

 

[fuzzyoctaves]

No need for a multiplexer block for that test either. Just connect the Out 4 and In 4 blocks together on the grid and Bypass the In 4 block to bypass the loop. When an In block is active it's fed by its associated jacks. When it's bypassed, it's fed by its input on the grid.

Ooh that's really helpful to know because I am thinking that I'll bypass the loop for high gain tones

 

[sprint]

Boost/Pad = 0 dB (interestingly, the noise goes down as I increase this

I use it to help with loop noise, but cautiously as it reduces digital output clipping headroom, 6 or 12 seems to leave me with enough room for the range of my guitar + sending a descent clean boost out to the external pre / pedal if desired, without clipping the output.