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[Marty America]

I bought a new Soundcraft Ui16 on Saturday. We used it on Sunday and it seemed okay. I was dinking around with it last night at home and I noticed that some of the input meters were bouncing around even though I didn't have any mics plugged in. Also, if I turn the output gain all the way up, I hear a hissing sound.

Is that why they call them "Soundcraft Ghost Preamps". But seriously, has anyone else noticed this kind of behavior?

[g'bye, Dick Rees]

If you solo it does it sound like Jerry Garcia?

[Gordon Brinton]

I bought a new Soundcraft Ui16 on Saturday. We used it on Sunday and it seemed okay. I was dinking around with it last night at home and I noticed that some of the input meters were bouncing around even though I didn't have any mics plugged in. Also, if I turn the output gain all the way up, I hear a hissing sound.

Is that why they call them "Soundcraft Ghost Preamps". But seriously, has anyone else noticed this kind of behavior?

If you see meter without any source, your input gains are probably too high. Your mic preamps are amplifying their own noise floor.

I have the Ui16. As with any mixer, it can get noisy if you are too liberal with the gains. I've learned to keep my input and output gains under tight control. I don't know how much you know about gain structure, but here is how I do it...
 
1. The input gain, (found on the GAIN screen,) should be thought of as not needing anymore than is necessary. Its function is to raise weak signals to a usable level, but not to raise already strong signals. Thus, I try to run my input gains so that my input meters bounce in the area of -24dBFS when in use, (fader between 0dB (unity) and +12dB). This generally provides enough signal to drive the mixer, but leaves enough headroom for peaks without distortion. (You'll notice that one fader notch is thicker than the others. That's the unity mark.)

2. Switching back over to the mixer screen, the channel fader meters should show various colors for a reason. The channel input signal, (shown in blue LED's,) and the channel output signal, (shown in green/yellow LED's,) appear all on the same meter. As you raise the fader, you should notice the yellow LED's rising. When you get the yellow LED's up to the same height as the blue, you have proper gain structure within the channel. (You don't need to have them aligned at the same height exactly, but it should at least provide a good starting point for output level. My channel faders usually end up anywhere between -10dB and 0dB (unity) depending on instrument or vocal.

3. My subgroups and master faders always remain on unity unless I temporarily need to lower something. My L and R output volume knobs, (hardware) run about one notch below full up. I understand that turning them full clockwise is about +3dB above unity and there shouldn't be any reason to go there.

4. I never use the channel (EQ and Comp) presets. Most of them are about as noisy as a Chinese newyears parade.

5. I have discovered that most of my noise (hiss) comes from the makeup gain on the compressors. If I push that up more than about +5 or +6 dB, they can really get noisy. I only use compression on a few things for level control and use the gain sparingly.

I notice the hiss more when using good quality in-ear-monitors to solo the main channel, but it is not nearly as noticeable through the FOH speakers. There will always be a little bit of noise there. I wouldn't lose too much sleep over it. It's a damn good sounding mixer otherwise.

I hope this helps. Good luck.

EDITED: To correct spelling, grammar, and clarity.

[Seth Albaum]

4. I never use the channel (EQ and Comp) presets. Most of them are about as noisy as a Chinese newyears parade.

5. I have discovered that most of my noise (hiss) comes from the makeup gain on the compressors. If I push that up more than about +5 or +6 dB, they can really get noisy. I only use compression on a few things for level control and use the gain sparingly.

I notice the hiss more when using good quality in-ear-monitors to solo the main channel, but it is not nearly as noticeable through the FOH speakers. There will always be a little bit of noise there. I wouldn't lose too much sleep over it. It's a damn good sounding mixer otherwise.

This much says maybe another software update is in order? You're calling out the reason I bought the thing, aside from wireless. It saved me a ton of money on rack gear. I suppsose I can tread lightly and make my own presets?

[Marty America]

Thank you for taking the time to write such a detailed explanation Gordon. I feel I have a good understanding of proper gain structure. That's what is puzzling to me. I've been doing live sound for thirty years. I know if I crank everything up, I will hear the noise floor but I don't have everything cranked. I just set my gains like I normally do. SM58's end up ~30db on the "LED" readout (not the meter) and that is consistent with my other mixers, A&H Qu-16 and a couple of Presonus mixers. It's also about where I would end up setting my analog consoles back in the day. I never saw my vue meters flicker on those boards.

The other thing that makes me suspect something is amiss is that I don't see it on every channel even though I have them set exactly the same. I can cut and paste all the settings and set the gain to identical values but I only see meter deflection on channels 1, 3, 4, 8, 9, 11, 12. What's more, it varies quite a bit. Some channels, no noise. Some channels the meters read up around -65.

As far as eq and compression, I'm afraid there isn't much getting around using them. That's just the nature of the beast.

[Gordon Brinton]

That's the same with mine. As I push the gain upward, +30dB is about the point where I start to see meter flicker and actually hearing the noise floor. That seems like a lot of gain to me though, maybe because I use higher gain mics than the Shure SM line, (N/D767a for male vocals and Heil PR22 for female vocals.) My mixer is still set up from a previous band rehearsal and no channels are set higher than +14dB on the gain screen LED readouts, (not the meters). Most channels are set below +10dB and a few, (keys and guitar processor direct,) are set to 0dB. Even after EQ and compression, I do not notice the overall noise floor much at all at those levels. It's acceptable for a bar room gig.

I guess we should expect that a low budget mixer will have low budget mic preamps. Noise is the consequence.

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