Hello..
I am using a SM58 dynamic. The audio output is good enough only when the mic input level in the audio interface is set to almost maximum (say 90%, knob equivalent).
At 80% mic input level, I still need to keep the mic at a distance of 5cms from the vocal source.
Between 60-80%, it is no longer singing but shouting.

Can something be done about the mic input level in the interface so that I can record vocals from a distance of around 20cms?
 
I did a bit of web search and found that it could be because of the impedance factor of the mic and the audio interface. But did not find any solution.

Thanks,
Kane

58's are normally pretty hot mics. My guess is that the problem's one of the following: a) the microphone is broken, b) you've got a bad mic cable/connector, or c) the input impedance is too low on your interface.
 
Make sure phantom power is turned off, and try another mic cable. If it turns out to be (c), or if the interface simply lacks adequate gain because it's, um, crap, then you could invest in a cheap mixer for your initial preamplification and take its output into the interface's line input.

+1 to what Bit is saying. Especially the bad cables. 
It would help to know the name of the interface. 

a) mic broken possibility - broken, like physical damage? It is 6 months old and is yet to experience gravity. And phantom power for a dynamic mic?
 
b) cable/connector - the same brand/same quality cable works slightly better when I connect my guitar to the audio interface. But the original input-output problem still remains. The same quality cables are used in the store itself from where I got them.
 
c) interface - it is Roland UA33 Tricapture. If it is an impedance issue, is there anything like a transformer that adjusts the impedance variance of the microphone and the audio interface?
 
 
 
 
 

audiomyth 
b) cable/connector - the same brand/same quality cable works slightly better when I connect my guitar to the audio interface. But the original input-output problem still remains. The same quality cables are used in the store itself from where I got them.

What connector are you  using at the interface end?  If it's a 1/4" jack (like your guitar connector) there's a good chance you're using a line/instrument level input which would explain the very low level you're getting from the mic.

audiomyth
I am using a SM58 dynamic. The audio output is good enough only when the mic input level in the audio interface is set to almost maximum (say 90%, knob equivalent). At 80% mic input level, I still need to keep the mic at a distance of 5cms from the vocal source. Between 60-80%, it is no longer singing but shouting.

So many variables here...
FYI - I always refer to an input level as a trim control... When I say trim, it's the same as you saying "mic input level".
 
1: As Karyn says above, make sure you are using a proper XLR to XLR quality mic cable, not a 1/4" cable.
 
2: How powerful is the vocalist. One person shouting could equal another persons normal singing voice. If the voice is not very strong, 20cm is simply too far from the mic - especially a '58 or similar.
 
3: Why 20cm? A 58' has an exaggerated proximity effect and there comes a point of diminishing return. The distance should be determined by the tone and strength of the singers voice... not a pre determined number.
 
4: I love a '58, but let's not forget its primary use is a live mic. In a live situation most singers will "eat" these mics and in those cases I find a common area of trim level to be around 10 - 11 o'clock on most mixers. If the singer backed off to 20cm (other than during shouting) the trim would be much higher to accommodate.
 
5: Not all mixers/pre-amps are attenuated the same amount with the trim control. The reason you have the variable trim control is to adjust it as needed. As long as there is not a lot of noise being introduced, it really doesn't matter how high you have to run the trim.  (EG: I use to use a Roland/Sonar VS100 and had to run those trims really high on everything. I now use a Presonus interface, and all trims are relatively low. Both sound fine & neither is better, it's just the way they were made)
 
Just my thoughts...
 

audiomyth
a) mic broken possibility - broken, like physical damage? It is 6 months old and is yet to experience gravity. And phantom power for a dynamic mic?

A mic doesn't have to be dropped to be damaged. '58 mics are very robust and it is unlikely the mic is bad, but it could be. As for Phantom power, "BIT" was saying "make sure it is turned OFF".

(d) what Karyn said
 
Yes, there are impedance-matching transformers and active impedance-matching amplifiers, but they should not be necessary for a dynamic microphone unless you've got very long (> 100') cable runs.

 
It's very possible that this unit might have under speced pre amps and turning it up to 9 is actually where it belongs. Notice there is no pad. 
 

8-10 inches is pretty far for some voices on a dynamic mike.  If you are using a proper mic cable, then try closing up on the mike some.  At a foot away a 58 would probably sound pretty thin, but I use them mostly for live applications.  And I don't know how much gain the Tri-capture has.  The VS series had solid preamps, but the Tri is older, I believe.  If it has less than 60 dB of gain at a foot with a less powerful voice you are likely to have problems with pick up.  Simply close the distance but watch out for the proximity effect.

Cable: XLR to XLR
Phantom: off
I just need a comfortable distance (around 20cms appeared to be so) because I prefer to play the keyboard and record voice simultaneously. But I do get your point that 20cms is slightly too much to ask for with my present set-up.

But I think I will give a try to the option of impedance-matching transformers. After trying it, I will update here.

Thanks @ Bit, Johnny, Karyn, Coda & AT.....

Regards,
Kane