Noise (hiss) using SM57 and SM58 - should I swap to 2 condensors or fix the hiss?

[AngryMonkney]

Hey,
I have a problem with noise (hiss) on my tracks, please see the attached song for an example (start quite acoustic guitar piece shows it in particular).

I am recording stereo acoustic guitar. The only mics I have are a Shure SM57 and a Shure SM58 - so im using 1 near the 12th fret and 1 near the bridge.

Trouble is I need to turn the gain right up to get a decent (loud enough) signal with these mics, but then I also get a lot of noise (hiss). I dont notice the hiss when singing into them, only when doing quite stuff like acoustic guitar (singing is lounder and more directed I guess). It doesnt seem to matter if I turn the gain up on the mixer, or in my recording package the hiss is still there.

Would you expect this hiss with these mics (im going into a Presonus FP10) in which case maybe I should get 2 small matched condesors?

Or would you expect their to be very little hiss in which case I should look to fix the problem (maybe I have a dodgy FP10, but I dont want to go down that road unless im certain its not just the mics).

Thanks,
AM.

[Hugh Robjohns]

The SM57 and SM58 have a sensitivity of just 1.9mV/Pa, which is very low. Not a problem with someone bellowing into it from a centimetre away, but not ideal for a delicate acoustic guitar.

As a result, you're going to need a shed load of gain from your preamp, and most budget preamps just aren't very quiet. Moreover, the noise often increases with more gain, which is exactly what you're found.

In contrast, a condenser mic, like the Rode NT5 as a reasnable budget alternative, has a sensitivity of 12mV/Pa which means you'd need 16dB less gain than for the Sm57/58.
And that would make the results significantly less noisey, obviously!

Go further up market, and the sensitivity generally iproves too. So the Neumann KM184 has a sensitivity of 15mV/Pa (meaning 18dB less gain) and the Sennheiser MKH40 at 25mV/Pa would need 22dB less gain!

So yes, capactor mics would be a useful step forward for you.

Hugh

[AngryMonkney]

Thank you Hugh,
Thats extremly helpful.

Just before I go and buy more mics (im eager to save cash if I can )

I have a small 4 channel mixer as well. If I were to run the mics into this small mixer and up the gain, then go into the FP10 would that help (instead of going straight into the FP10 and upping the gain there)?

Or does it totally depend on the quality of the pre-amps in the 4 channel mixer then (i.e they may be just as poor as the FP10s in which case theres no point, or they may be better in which case it could work)?

Hopefully I havent explained that too badly to understand
Thanks,
AM.

[Hugh Robjohns]

I have a small 4 channel mixer as well. If I were to run the mics into this small mixer and up the gain, then go into the FP10 would that help (instead of going straight into the FP10 and upping the gain there)?

Possibly. One way or the other you still need a mic preamp to boost the signal, whether it is the mic pre in the mixer or the mic pre in the interface. The mixer mic pre might be less noisy at high gain than the interface preamp.

Can't say whether it will be better or not because I'm not that familiar with the equipment mentioned (or not mentioned in the case of the mixer ) You'll just have to try and see.

But the bottom line is that you are asking a lot for a budget preamp to get a usable low-noise signal from such a quite and delicate source with such insenstitive mics.

Hugh

[Jeraldo]

Go further up market, and the sensitivity generally iproves too. So the Neumann KM184 has a sensitivity of 15mV/Pa (meaning 18dB less gain) and the Sennheiser MKH40 at 25mV/Pa would need 22dB less gain!

And even further up market but a lot lower in price, the Beyer MC930 is at 30mV/Pa.....