Audio Interface Noise

[JahooRoisym]

Hi everyone!
I am writing in a desperate hope of getting help. At first I have to mention that I’m new to recording and mixing so I might babble with no sense.

To say thing shortly – my audio interface (PreSonus AudioBox USB) produces annoying hissing noise. While for music the signal to noise ratio may suffice, for voiceovers it’s just plain bad.

When I arm the track and set monitoring in Ableton Live to ‘auto’ (or ‘in’) I can clearly hear the noise and the Lives Spectrum analysis (from Audio Effects) shows that it’s at around -118 dB and that’s with the input gain knob on the Audiobox set all the way down (even with the mic unplugged). So it would seem that the internal noise of the interface is at around -118dB.

When I record a normal voice at a few cm from my Rode NT-2 mic, with the input gain set at 50%, the peak of the voice in the spectrum is -40 dB. One of my test samples is here:
normalized, raw - soundcloud.com/jahooroisym/hiss-test-normalized (sorry, forum rules won't let me past an URL)

My main question is: is the noise floor of -118dB normal?

Things that I THINK I ruled out so far:
1. Ground loop – nope. Tried it on laptop running on battery, with no audible effect (the Audiobox is USB powered btw).
2. Bad/noisy PC – nope. Apart from my main desktop I have tried on a new Sony VAIO laptop with the exact same effect.
3. Bad/noisy environment/mic – nope. As I said the -118 dB noise is there even regardless of the mic being plugged in. When I have the mic plugged in, the noise floor is raised only when I turn my input gain to as high as 60% (about 1-o’clock). So it’s it not the mic nor the noise in the room.
4. Bad interface – might be, but not sure. I borrowed an Alesis Multimix USB from a friend to compare as this was my first thought. Turns out the Multimix also produces the noise floor of around -120db - its only slightly better than the Audiobox. This is when I became a little depressed as I started to suspect I am doing something horribly wrong.
5. Other things. I tried different cables, different usb sockets, recording in different rooms and even apartments, all with the exact same effect.

So either I’m unlucky and both the Audiobox and Multimix have just bad pre-amps or other internals, or I’m doing something wrong. The bottom line is – the recorded voiceovers are very bad. I tried using the Izotope RX2 denoiser but at this rate of signal to noise there are lots of artifacts.

Any help or suggestion would be gladly appreciated.
Thanks in advance

Jahoo

[Bobbsy]

A noise floor of -118dB isn't just normal...it's actually very good.

I suspect you have a few things going on here. First, recording extremely low (-40dBFS) doesn't reduce your noise level if you then have to normalise later. When you add 30 or 40 dB of level to your voice, you're adding exactly the same amount to your noise. You should be recording with your voice peaking at between -14 and -10dBFS which is equivalent to between PPM5 and PPM6 if you're used to European style PPM meters. You need a microphone and pre-amp combination that lets you record at these levels without noticeable noise.

I've never used the interface or mic you have so don't know what you should be able to expect. However, after listening to your sample, I suspect that it might be a combination of your mic needing a better pre-amp to get sufficient level and the Presonus becoming noisy when you turn the gain up sufficiently for the microphone. Perhaps somebody who knows the Audiobox will pop in and let you know if this is normal or if you have a faulty unit.

The solution? An interface with better (i.e. quieter) mic pre amps or a mic with a higher output level--or both. As you say, for voice work you need a better S/N than for music. However, I have to say that, based on your sample, you also have some room noise/acoustic issues on top of the electronic hiss.

[musicmachine]

Have you tested both channels on the audiobox separately? I had one that made noise in the left channel but not the right.

[JahooRoisym]

Been a while since I've visitet the forum. Thanks Bobbsy - I did exactly what you suggested and turned out this in fact was my problem.
Sorry I forgot to write anything back then.