"Hiss" on my new Focusrite VM Pro

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JoeW

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I've been having trouble getting a clean signal on this new equipment. Here's the chain...

CAD M9 tube mic > Focusrite VM Pro > Edirol UM-25 > computer Hard drive located in the next room. Pretty simple, yes?

The cabling from the Cad mic into the VM pro is a balanced XLR, and from VM Pro to Edirol is balanced XLR also.

Doing straight voice/narration I would expect a nice clean sound (using no compression or other processing offered by the pre.)

Instead, what I've been getting is a very noticable background "hiss" - sounds almost like tape hiss. This is in a small 7X10' sound-proofed room...no external noise coming in to explain this "hiss" sound. The computer is in the next room.

I am monitoring this on line level output to headphones, directly out from the A/D interface.

If I bypass the pre and take the mic directly to the Edirol A/D via balanced XLR, "voila", I get a very clean, nice signal with none of the hiss. The hiss goes away...no noise.

The sales guy where I bought the equipment suggested that there was some impedence (phasing?) mismatch in using an XLR from the mic to the pre and then from the pre to the A/D, and suggested I try using the balanced TRS patch cable instead.

I'm skeptical...wouldn't a balanced TRS give the exact same signal as a balanced XLR?? Just different plugs...right?

I am begining to think the Voicemaster Pro is defective. Just to be sure, I've ordered a TRS balanced cable that I will try, just to eliminate that possibility.

Does any of this make sense?

All ideas appreciated!!

Thanks,
Joe
 
I have a VM Pro and get no hiss at all so that may be a defective unit. Not sure if it is in a rack or not but I burned up my first unit because it needs air to stay cool. These units run very hot the point of, if there is no air around it, freaking out.

My current unit is racked with spack above and below and I have put a few miles on it with no problems. Going on 1 1/2 years with this unit.
 
I really don't have mice going into my pre...

Wow...you're the only person I've run into who's using the VM Pro!

Perhaps you can give me your recommendation for setting the gain and fader on the pre.

Cad tube mic going into VM Pro...what's the best "starting" setting on the gain?

VM Pro going into the Edirol A/D...what's the best "starting" setting on the out put fader?

And..another question: Should I see the VU meter registering with your settings? Mine stays down in -24db level consistently for straight voice.

Final question: is there any signal difference - going from the VM to the Edirol - between a balanced XLR and a balanced TRS?

This is driving me nuts!

Thanks a lot for your input!
 
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My brother has the voicemaster pro, and I've used his a bit, so I know it but am not an expert.

You don't say how you have the VM Pro configured. What modules are in and what modules are out? I would suggest turning all the features off except for the preamp. Then, if necessary turn on the compressor and maybe the de-esser if you need it. That's all that should be on. If the unit is operating correctly that should give you plenty of clean gain. The other features can add a lot of hiss and high end grit.

What my brother was doing wrong was he had the gain on the preamp fairly low, and was making it up throughout the rest of unit. So if you haven't done this already, turn the preamp volume very high and bypass the rest of the unit. Hopefully that will help.
 
Thanks for the input...

I've got all the modules turned off. Just running the mic into the voicemaster and out to the A/D box with no processing. I've got gain set to 0db coming in, and fader set to 0 going out to the A/D.

Tweaking either or both of these settings affects volume, but not hiss.

Shouldn't I be able to run straight through and get a clean signal?

Thanks!
 
JoeW said:
Wow...you're the only person I've run into who's using the VM Pro!

Perhaps you can give me your recommendation for setting the gain and fader on the pre.

Cad tube mic going into VM Pro...what's the best "starting" setting on the gain?

VM Pro going into the Edirol A/D...what's the best "starting" setting on the out put fader?

And..another question: Should I see the VU meter registering with your settings? Mine stays down in -24db level consistently for straight voice.

Final question: is there any signal difference - going from the VM to the Edirol - between a balanced XLR and a balanced TRS?

This is driving me nuts!

Thanks a lot for your input!
Click to expand...

Lot's of people here have one. Do a search.

RE:Your ??s

Perhaps you can give me your recommendation for setting the gain and fader on the pre. This varies by mic and line signal so there are no magic settings but SonicAlbert is right on for getting a clean signal.

Cad tube mic going into VM Pro...what's the best "starting" setting on the gain? The approach I take is to set the output gain in the middle and then adjust the input gain as needed. If the signal is too hot I decrease the input. If its too low I turn up the input unless it's already maxing out. In this case I then work on the ouptut until I reach a nice level. Then I work on my A/D levels. Generally the lower you can keep the input, the cleaner the sound. That should get you in the ballpark.

VM Pro going into the Edirol A/D...what's the best "starting" setting on the out put fader? See above. Get a nice clean signal first and then adjust the output to match your convertors. If however, you want a little grit, push the input levels and lower the output.

And..another question: Should I see the VU meter registering with your settings? Mine stays down in -24db level consistently for straight voice.This will vary depending on the mic. I try to keep the levels bouncing against the meter at -3 or even slightly lower.

Final question: is there any signal difference - going from the VM to the Edirol - between a balanced XLR and a balanced TRS? Nope, just different connectors.
 
Thanks for this response...it only strengthens my confidence that I've been approaching this correctly.

I spoke with the tech person at Cad mics earlier and described my problem to him. His first reaction is that the tube is bad and offered to ship a replacement out to me....no questions asked! (about proof of warranty, etc.)

I'm impressed with this kind of responsiveness, and Cad is to be commended.

I'll put the new tube in as soon as I get it and see what the effect is.
 
A good percent of the time, if you get hiss in a chain and a tube mic is involved, it will be the tube.
 
arcaxis said:
JoeW,
Not sure which way to interpret what you said about input gain set at 0db, so just to be sure, is the input gain control set to 0db or are you setting the input gain control to get the LED meter to a 0db level (not hitting the red O/L LED). The Users Manual describes how to set the levels fairly well and I assume you read through this.
The Output Peak meter monitors the level of signal as adjusted with the Output Fader you're sending to the Edirol. At -24db I wonder if you're kicking up the gain in the Edirol to compenate for low signal and thus bringing up the hiss with it.
Do you get the hiss with the mic unplugged from the unit leaving the controls as they are? And do you have a second mic to try?[/QUOTe

OK...I (hopefully) am getting a handle (an understanding) on this. Tell me if I'm on the right track...

The mic outputs at -50db, so to achieve a 0db level at the pre, I need to adjust gain at +50 db?

What I have been doing is setting the gain on the amp at 0db, so the noise floor level is going to be high when I output to the A/D interface.

There will always be some ambient background/electronic noise...correct? In which case, I've not been giving enough gain to make for an adaquate signal to noise ration? This would cause the noise floor to be more apparent to me.

I've readjusted my thinking and believe I am achieving a proper signal level now with "acceptable" noise floor. Am I making sense in this?

Thanks a LOT to all of you...it's through your comments and insight that guys like me can learn what the hell we're doing!
Click to expand...
 
Middleman said:
A good percent of the time, if you get hiss in a chain and a tube mic is involved, it will be the tube.
Click to expand...


You know, I talked to the tech guy at Cad Mics and he's sending me a new tube...just to be sure. Didn't even ask for warranty info. Nice kind of a company to do business with.. no?
 
Okay, as I'm sure you noticed, on the VM Pro Input Gain knob there are two "zero" settings. The numbers that are in the black circles are for the line inputs, and the other numbers are for the mic. So if you are setting the mic input gain at the zero that's in the black dot, that is not the right setting. And of course, if you are setting the mic gain at the other zero setting, that is completely wrong too.

Your ideal mic gain setting is most likely between +40 and +60.

If I understand you correctly now, you had your mic gain extremely low. So what you were doing is this: you were attempting to amplify the signal up the level it needed to be, but later in the signal chain, after the VM Pro. But since the mic signal was just a little louder than the noise floor, you were also amplifying *a lot* of noise and hiss along with the signal. So the mic signal and the noise floor were very close together, and when amplified, they both are still close together. But you can hear all the bad hiss because it is so much louder.

So again, a mic level setting of +40 to +60 is what you need. Anything less than that will be less than optimal. Of course, it might be a bad tube too!
 
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Albert...Thanks!
Yes, I've had my mic gain set way too low, so....as you say, I had the noise floor very close to the mic gain and was getting all that awful hiss!
 
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