Mic/Line Noise Troubleshoot - Seeking Advice - Help Please

M

MoBettaBlues

New member
I'm trying out some SDC's and I am noticing a lot of "noise". I'm not sure if it's just a noisy preamp, AC noise, etc?

The first half of the track is "Mic #1" on the left channel. The second half is "Mic #2" on the right channel. You'll hear the noise come in as I turn up the mic pre. These are on 2 separate per's. Mic #1 has some different noise than mic #2 as well.

Mic pre is Focusrite Saffire Pro 24 DSP.

I shut off my lights and computer monitor to make sure it was not a factor.

Hoping for some ideas.

I know it could be cables but not sure the easiest way to go about troubleshooting.

https://soundcloud.com/jeff-vivrette/mic-noise

Side note: 1 channel seems to have more gain than the other. Not sure if it's the mic or what. Any recommendations on how to test my equipment?
 
The noise can be seen in the attachment and is a wide band "whine".

This can be a characteristic of USB noise, Win 7 levels wrongly set or something being picked up on the cables. These last would have to be very cheap ***to be that vulnerable but a continuity check, especially of the screen it always a good idea.

Next step is to replace the mics with a dummy plug, an XLR with 120 Ohms metal film resistor soldered across pins 2 and 3. Moving same about the room should enable you to check if anything is radiating crap.

With a dummy load and with gains set for "realistic" levels I would expect the noise level of the Focusrite to be better than -80dBFS and that to be hiss, virtually no 60Hz or harmonics (but you almost always get a blip at 50/60Hz).

Dave.
 

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Thanks for the detailed response Dave.

ecc83 said:
The noise can be seen in the attachment and is a wide band "whine".

This can be a characteristic of USB noise, Win 7 levels wrongly set or something being picked up on the cables. These last would have to be very cheap ***to be that vulnerable but a continuity check, especially of the screen it always a good idea.
Click to expand...

Sorry for my ignorance but how would I perform a "continuity check"?

ecc83 said:
Next step is to replace the mics with a dummy plug, an XLR with 120 Ohms metal film resistor soldered across pins 2 and 3. Moving same about the room should enable you to check if anything is radiating crap.
Click to expand...

I'll make a dummy plug and try this.


ecc83 said:
With a dummy load and with gains set for "realistic" levels I would expect the noise level of the Focusrite to be better than -80dBFS and that to be hiss, virtually no 60Hz or harmonics (but you almost always get a blip at 50/60Hz).

Dave.
Click to expand...

What is assumed to be a realistic level for gain? I think the noise becaome more prevelent when my gain starting approaching 75% of max.
 
Sounds like noisy gain pots combined with 'normal' mic noise at high gain to me. The first pot maybe worse than the second because that channel gets more use?

Set your gain so your voice/guitar/whatever through the mic is hitting anywhere between -18dB(FS) to -10dB(FS) in your DAW and see if it's noisy. You shouldn't realistically need to have the gain up to 75% - between 25/50% is more the target.
 
"Realistic levels" ?
Set gain for ~ -20dBFS with the SDC about afoot from mush and reciting "Mary". Unplug mic, plug in load.

"Continuity check"? With a digital testmeter on the Ohms range check mic cables pin 1 to pin 1 etc. Each pin should read very low, well under one Ohm to its mate.

Dave.
 
Hi guys,

Interesting info above - thanks for sharing.

MoBettaBlues, if you have any concern about the condition of your pre-amps, please contact us and we can sort out a service for you and check over the unit to ensure its up to spec.

It would be useful to hear some examples of this noise too. Our log gain pots have large amount of gain between roughly 7.5-10 to accommodate to a larger range of signals. However, this can sometimes introduce noise just by the shear nature of how much gain is being applied.

Please let us know the results of your tests or contact us through our site! (focusrite.com)


Best,

Miles
 
Hi Miles,
SOOOOO nice to see a contribution from "The Trade"! It is such a rare event on forums I thought I should point it up.
I can understand the reluctance to some extent, you can open yourself up to abuse! But most of the folks at HR seem fairly civilized? (shutup Greg!)

On a personal note, you might have noticed I have been a bit hard on the 2i2? This is really only a gripe about the instrument headroom which has now been fixed (mind you, I think lack of MIDI was a boob! The similarly lacking Tascam 2000 has sunk virtually without trace!) .

I have an 8i6 but have not had time to get really into it but performance wise it seems on a parr with my KA6.

Rock Miles,
Dave.
 
Miles@Focusrite said:
Hi guys,

Interesting info above - thanks for sharing.

MoBettaBlues, if you have any concern about the condition of your pre-amps, please contact us and we can sort out a service for you and check over the unit to ensure its up to spec.

It would be useful to hear some examples of this noise too. Our log gain pots have large amount of gain between roughly 7.5-10 to accommodate to a larger range of signals. However, this can sometimes introduce noise just by the shear nature of how much gain is being applied.

Please let us know the results of your tests or contact us through our site! (focusrite.com)


Best,

Miles
Click to expand...

Miles,
Thank you very much for chimming in here and your offer of support. I will certainly contact you should this be the case.

Regarding examples of the noise, please let me know if I can provide anything in specific and I would be happy to do so. The example provided in my first post was a short example/test.

I will post more after I have a chance to conduct the tests others have advised on this post. Just waiting for the parts to arrive for my XLR dummy load plug. Should be here today or tomorrow.

Again, thanks for jumoing in. Greatly appreciated.
 
Some numbers for my 8i6 (I am guessing all Focusrite AI pres are similar?)

XLR terminated 230R (nearest I had!)
Gain max. -72dBFS peak, -85dBFS rms

Gain min. -93dBFS peak, -101dBFS rms

The figure were the same for both left and right channels which indicates very good QC IMHO. The results are the playback figures using Samplitude SE8 (because it has metering that gives a numerical readout below the indicated bargraph).

I would consider these specification easily good enough for all applications save perhaps speech recording in a VERY quiet room, we should be so lucky!

I shall try the same tests for my NI KA6 soon but I would expect the results to be comparable. There are "technical" reasons why this is about as good as you can get with a "single knob" pre amp!

Dave.
 
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