Noise floor

[underscore11]

Hi wonderful people of the Reaper forums! I have a bit of an issue, its more of a hardware related type issue but thought maybe I could get some answers here.
So basically, in short, my audio interface omits a white noise (which I'm guessing is the noise floor?) at about -90db with the preamp gain on 0. When I crank the gain, this white noise shoots up to -60db. This is without anything plugged in. My question is, is this normal? Maybe I'm being picky, but this noise really interferes with any instrument that needs a slight gain boost. My main annoyance with this is when I try to use a virtual amp and cab vst for recording electric guitar, the inevitable gain of the virtual amp always amplifies this nasty white noise. I have tried clean boosting my guitar signal before hitting the interface (with the interface preamp gain down all the way) but still that nasty white noise still exists in the signal. Any ideas on how to resolve this? My latest theory is that it might be some sort of grounding issue. Oh and I'm using a Focusrite Scarlett 8i6 (1st gen) which I'm aware some people have had similar issues with.

[DVDdoug]

All active electronics generate some noise (white noise/hiss). Any amplification will amplify that noise. A better preamp will generate less noise. You can't do much about preamp noise (other than buy a better preamp or interface).



...With guitar you shouldn't have to turn the recording level all the way up.

-60dB isn't that bad if you have a strong signal... It's the signal-to-noise ratio (SNR) that's important. You can turn-down the noise by turning-down the knob, but you are also turning-down the signal.


If you are making a mix that will help with the SNR. If you have a dense mix with no quiet parts you'll never hear the noise! A solo voice or solo acoustic instrument is the hardest to record...


Turning-up the guitar volume will increase the signal (although I'm sure it's already all the way up), as will a hotter pickup or simply playing louder...


The "gain" control is usually an attenuator in front of the preamp circuitry, or in-between the preamp and the analog-to-digital converter. Since it's turning-down the noise, I'd guess it's in front of the ADC. In that case, changing the recording level doesn't make any difference because you are adjusting the signal and noise together.


As a guitar player you probably know that a guitar (or your body) can pick-up power line hum (from the electrical wires all-around you). Usually, hum/buzz is the biggest issue with electric guitar.


And, "grounding issues" are usually related to power line hum.


Noise can also get into the electronics through the power supply. With an old-style linear power supply you can get regular-old hum. Modern switching supplies usually operate above the audible range so it's less of a problem.


With USB powered interfaces you can noise from the USB power which is usually very noisy and if that noise gets into the analog electronics it's usually a high-pitch "whine". Some computers are worse than others and some interfaces are better filtered than others so you never know who to blame...


If you record with a microphone, room noise is almost always the biggest issue. The head preamp in a condenser mic also generates some noise, but it's usually an excellent low-noise circuit and since a condenser puts-out a hotter signal than a dynamic or ribbon mic, that gives you a better SNR overall with the preamp. (A hotter mic makes no difference with acoustic room noise).

[JamesPeters]

Originally Posted by underscore11

my audio interface omits a white noise (which I'm guessing is the noise floor?) at about -90db with the preamp gain on 0. When I crank the gain, this white noise shoots up to -60db. This is without anything plugged in....Oh and I'm using a Focusrite Scarlett 8i6 (1st gen) which I'm aware some people have had similar issues with.

This is absolutely normal and not a problem at all.

Even for a guitar (DI) you shouldn't have to crank the gain. If the gain is halfway (with the input set for instrument) you'll get around -80 dB fs noise. That gives you plenty of SNR. Remember, you don't want to record with signal peaking up to around 0 dB anyway; leave some headroom (around -12 dB is fine).

-60 dB seems like a lot but that's only with the preamp gain cranked. The last bit of gain the preamp gets, yes it suddenly gets noisy, but that's a range you shouldn't have to use. If you have to crank the gain of that preamp, you're using the wrong mic and/or trying to record mouse farts. I wouldn't want to use an SM7 for quiet sources with these preamps, for instance. Try a more sensitive mic though and it's more than enough gain for pretty much everything.

[Allybye]

I hope this post can also help with some context and suggestions for you to check....
"When I crank the gain, this white noise shoots up to -60db. This is without anything plugged in."

If that is truly what you mean then it is not the best way to measure noise.
Many amps exhibit higher noise (usually heard as hiss) with nothing connected to an input. Connect a source and the wideband noise usually drops. Note the interfaces mic spec is with a 150ohm source connected!

Secondly can you clarify which input you are using for the guitar? It ought to be the instrument input to avoid loading the guitar too much and thereby loosing signal. Switching from line to instrument inputs (from the user guide -I am not familiar with the specific interface) is via their supplied software. If you use line input there will be a big loss of gain. Incidentally often the issue can be too much signal rather than too little signal.

Please do note the two previous posts as well but if you are using FX that increase frequencies that are those with the low level hiss it will make the SN ratio worse and if that is combined with low signal too....

Although you call it white noise if it is really some high frequencies then it might be from a digital source such as from USB interference.
Or you might just have some noisy sources? or an open source (nothing connected) with it turned up?

If you can substitute the sources with resistors (200ohm. for mic inputs, same for line sources and 100kohms (an approximation only!) for a guitar direct and see if your results change.

Many an interface is quite good regarding noise with not a great deal to choose between them. I have noted comments that the Focus might not be great at high gain levels (it may or may not be but is ok according the the spec, no better) but as writ above you should hardly ever need to use at high gain. Something is wrong if you do need to do so with an electric guitar. If it is a miked acoustic that can be a different matter!