Contributor - Level 2

Gain Sanity Check

I've connected an SM57 to the XR18 and running via USB to Logic Pro X. Recording an acoustic guitar with the SM57 about 6" from the 15th fret.

In order to get a level in logic pro of -18 or so, I need to set the gain on the XR18 to about 40. This seems very high to me given the other posts in this forum. Moving the mic closer doesn't make a significant difference. Lowering the XR18 gain into the 25 range gives me a logic pro level of -20 to -30.

On the XR18, I'm seeing about 20 peak on the fader meters with gain at 40. I've tried multiple inputs on the XR (including 1), and I've tried different XLR cables between the mic and the mixer.

I don't have a very good understanding of the different meter scales, so I'm focused on the one in Logic Pro (which I believe is dBFS) and target about -18 to -12 for recording levels. The reading of 20 on the XR18 is whatever 20 represents on the fader meter scale.

Does this sound like a reasonable gain setting on the X-Air? Am I missing something else?
RobertRothe Contributor - Level 2 01-04-2019

01-04-2019

Gain Sanity Check

I've connected an SM57 to the XR18 and running via USB to Logic Pro X. Recording an acoustic guitar with the SM57 about 6" from the 15th fret.

In order to get a level in logic pro of -18 or so, I need to set the gain on the XR18 to about 40. This seems very high to me given the other posts in this forum. Moving the mic closer doesn't make a significant difference. Lowering the XR18 gain into the 25 range gives me a logic pro level of -20 to -30.

On the XR18, I'm seeing about 20 peak on the fader meters with gain at 40. I've tried multiple inputs on the XR (including 1), and I've tried different XLR cables between the mic and the mixer.

I don't have a very good understanding of the different meter scales, so I'm focused on the one in Logic Pro (which I believe is dBFS) and target about -18 to -12 for recording levels. The reading of 20 on the XR18 is whatever 20 represents on the fader meter scale.

Does this sound like a reasonable gain setting on the X-Air? Am I missing something else?

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Super Contributor - Level 2

Re: Gain Sanity Check

Hello Robert,

You may have seen others recommend a gain setting of around 25dB for the SM57 but that was probably for drums or rock vocals. The SM57 is a relatively insensitive mic (-56dBV/Pa) and an acoustic guitar is quiet compared to these other uses. A pre-amp gain of 40dB is not unreasonable in this case.

I usually run my condenser instrument mics with gains around 20-30 dB for acoustic guitars but these mics have 10-20 dB more output than the SM57 so it is equivalent to your 40 dB.
Contributor - Level 3

Re: Gain Sanity Check

As above. The difference between a close-mic’d snare or e-gtr cab with a high SPL vs an acoustic gtr 6” away (remember the inverse square law) would account for the ~15dB increase in preamp gain required to hit -18dBFS on the meters.
Contributor - Level 2

Re: Gain Sanity Check

Rex / Craig: Thank you for the answers and for explaining the "why" behind the answers -- this is very helpful. My mic collection is limited, but I do have a Behringer B1. Would this be a better choice?
Super Contributor - Level 2

Re: Gain Sanity Check

Robert Rothe;158168 wrote:
Rex / Craig: Thank you for the answers and for explaining the "why" behind the answers -- this is very helpful. My mic collection is limited, but I do have a Behringer B1. Would this be a better choice?

That depends on whether you're happy with the sound you get with the SM57. Mic choice is a personal thing for Sound Engineers - often based on experience of using different mics in various circumstances.

The B1 would give you about 20 dB more output and a more balanced frequency response. In particular, the low frequencies would be more pronounced. In a studio environment this may be helpful but I personally wouldn't use it on an acoustic guitar in a live situation. Large diaphragm condenser mics will often pick-up too much unwanted sound from other instruments or air movement in a live performance. You can EQ it out but then it may not sound any better than the SM57.

I prefer small diaphragm condensers for live acoustic guitars. My favourites are some 30 year old AKG C451E/CK1s but I've also had good results with Rode NT5s.
Contributor - Level 3

Re: Gain Sanity Check

The short answer is "it depends."

A longer answer is as follows.

The B1 has a hotter output, so in theory you won't have to crank the preamp gain as much to get levels up to -18dBFS. The thing is, the more sensitive the mic, the more sound it will pick up (or you could look at it as having a higher noise floor,) so if you're in a less-than-ideal room, a more sensitive mic may not be a good thing. Furthermore, cranking the gain is really only a problem if it distorts or induces too much noise\crosstalk etc into the signal. This isn't such an issue for modern preamps as it was with preamps built a few decades ago. According to the XR18's spec sheet, with a preamp gain of +40dB you've still got another 20dB of headroom if you need. All that said, a mic's sensitivity is only one consideration when considering which mic is "better." What you really should be concerned about it the overall "sound" of the mic.

Both mics have a different frequency response, different pickup patterns (though they're both cardioid, the frequency sensitivity will vary with directivity differently with each mic,) different transient response, different max SPL etc. Although one mic may be "better" than the other on paper, the supposedly "inferior" mic could sound better for the particular instrument you're playing, in that particular room. Eg according to the specs sheet the B1 has a more linear frequency response (especially below 4kHz) than the SM57, however the SM57's frequency response (particularly the rolloff below 200Hz, which is superior to the B1's -6dB/octave switchable HPF @ 75Hz,) may be better suited to recording your acoustic guitar than the B1.

My advice is to try both and see.

Edit: as above.
Volunteer Moderator

Re: Gain Sanity Check

Hi Robert,

As always Rex and Craig have provided you excellent and extensive advice regarding gains. One question has not been asked though, is if the SM57 is a genuine Shure SM57 or a Chinese knock-off. A friend of mine was complaining about his SM57 not having much gain and I loaned him one of mine. He was shocked to hear the difference. His was a knock-off.

Regarding the B1, as already mentioned, these large condenser (LC) mics are much more sensitive than a dynamic mic such as the SM57. That also means that they are more proned to feedback in a live setting if not properly EQ'd. I use LC mics for picking up larger groups or choirs. When properly EQ'd they are amazing - when not EQd, they'll drive you nuts. A Shure SM58 on the other hand, simply rolling off the bottom end can (in a pinch) make it a good sounding mic.
Paul Vannatto, Volunteer Forum Administrator and Moderator
Contributor - Level 2

Re: Gain Sanity Check

Great advice from all. Thank you.
Contributor - Level 2

Re: Gain Sanity Check

Paul, I did consider that. However, I purchased the SM57 through GuitarCenter in the US. I'm hoping that if anyone was selling genuine merchandise, it would be them. I'm not sure how to tell the difference visually. If anyone believes I should question it further, please let me know.
Volunteer Moderator

Re: Gain Sanity Check

Robert Rothe;158181 wrote:
I purchased the SM57 through GuitarCenter in the US. I'm hoping that if anyone was selling genuine merchandise, it would be them.

I would think that would be the case Robert. Typically the source of the knock-offs are ebay, unscrupulous music store dealers that want to increase their profit margins, or a buddy that says they got this great deal for an SM57.

By the way, did you know that we used the SM57 as vocal mics before the SM58 came on the market (I still like the sound of the SM57 over the SM58)?
Paul Vannatto, Volunteer Forum Administrator and Moderator