Mic Gain Calculator: How Much Preamp Gain Do You Need?
Pick your microphone, say how you will use it, and see the preamp gain that puts your peaks at a healthy level. It shows whether your interface has enough clean gain and how much noise to expect.
Your microphone
Sensitivity is on the spec sheet. Presets are published or typical figures.
Your sound source
Rough averages. Pick the level you really use.
Close-up recording is 5 to 15 cm. 2.5 cm = 1 in.
About 12 dB for speech, more for percussive sources.
Average level at the mic: 83.9 dB SPL
Your preamp or interface
-12 to -6 dBFS is the usual target for peaks.
Often +18 to +24 dBu; check your interface's manual.
Typically 50 to 70 dB.
Equivalent input noise, e.g. -128 dBu. Lower is quieter.
Leave blank to ignore. Dynamic mics are usually negligible.
Gain needed
62.8 dB
Puts peaks at -10 dBFS.
Mic output at peaks
1.4 mV
-57.1 dBV, from 96 dB SPL peaks.
Average will sit near
-22 dBFS
A healthy speech average is about -18 dBFS.
You are 6.8 dB short
Signal to noise
61 dB
Clean. Average speech 84 dB over a noise floor of 23 dB SPL equivalent.
Why it matters
What happens if you move?
| Change | Gain needed |
|---|---|
| -6 dB louder at the mic | 68.8 dB |
| -3 dB louder at the mic | 65.8 dB |
| As entered | 62.8 dB |
| +3 dB louder at the mic | 59.8 dB |
| +6 dB louder at the mic | 56.8 dB |
| +12 dB louder at the mic | 50.8 dB |
Halving the distance to the microphone makes the signal about 6 dB louder, so you need 6 dB less gain.
What this assumes
What microphone gain does
A microphone makes a tiny voltage. The preamp lifts it to a usable level.
A microphone turns sound pressure into a very small voltage. Its sensitivity says how small: how many millivolts it makes from 1 pascal, which is about 94 dB SPL. A dynamic microphone like the SM7B makes only 1.12 mV at that level, while a typical condenser makes around 15 mV, roughly 22 dB more.
The preamp in your interface or mixer multiplies that voltage by its gain, measured in dB. Too little gain leaves a quiet recording with a high noise floor. Too much clips the converter, and clipped audio cannot be repaired.
The mic gain formula
Four numbers decide how much gain you need.
- Sound level at the mic. Speech is about 62 dB at 1 m and gains 6 dB every time you halve the distance. At 8 cm that is 84 dB SPL.
- Mic output. Microphone level = sensitivity + (SPL − 94 dB). The SM7B at 96 dB SPL peaks outputs -57 dBV, which is 1.4 mV.
- Target at the converter. Your interface's 0 dBFS corresponds to a certain input level, often +18 dBu. Peaks at −10 dBFS therefore sit at +8 dBu.
- Gain = target level − mic level. dBu and dBV differ by 2.22 dB, so the SM7B's -57 dBV is -54.8 dBu, and the gain needed is 8 − (-54.8) = 62.8 dB.
Different microphones need very different amounts of gain for the same job:
| Microphone and distance | Sensitivity | Gain needed |
|---|---|---|
| Shure SM7B at 8 cm | 1.12 mV/Pa | 63 dB |
| Shure SM58 at 8 cm | 1.85 mV/Pa | 58 dB |
| Typical condenser at 20 cm | 15 mV/Pa | 48 dB |
What level to aim for
Set gain so your loudest moments peak between −12 and −6 dBFS.
Digital audio is measured in dBFS, decibels below the absolute maximum. The conventional target is to have your loudest peaks land between −12 and −6 dBFS, which leaves room for surprises and puts your average speech near −18 dBFS.
| Where it lands | Meaning |
|---|---|
| -6 dBFS | Strong peaks, the upper limit of the target window |
| -12 dBFS | Comfortable peaks, a good aim |
| -18 dBFS | A healthy average level for speech |
| 0 dBFS | The ceiling. Anything above clips and cannot be repaired |
The calculator assumes speech peaks sit about 12 dB above its average. Percussive sources have a bigger gap, so raise the "peaks above the average" field for those.
Low-sensitivity mics and preamp noise
Needing 60 dB of gain is only a problem if the preamp is noisy.
Many broadcast dynamic microphones have low sensitivity. That is fine on a quality preamp, but a budget interface can run out of gain or add audible hiss by the time it is turned up that far.
The calculator estimates this with the preamp's equivalent input noise (EIN). A preamp with −128 dBu EIN is equivalent to a sound of about 23 dB SPL at the SM7B, leaving a signal-to-noise ratio of about 61 dB for speech at 8 cm. Halve the distance and it improves by 6 dB.
If you do not have enough gain
- Move closer. Halving the distance adds 6 dB of signal and removes 6 dB of required gain, for free.
- Add an inline preamp. These sit between the microphone and the interface and add roughly 20 to 30 dB of clean gain, and many are powered by the interface's phantom power.
- Use a more sensitive microphone, such as a condenser, if the room allows it.
Mic Gain Calculator FAQ
+ How much gain does an SM7B need?
About 63 dB for normal speech at 8 cm, aiming for peaks at −10 dBFS on an interface where 0 dBFS is +18 dBu. Its sensitivity is only 1.12 mV/Pa, so many interfaces struggle, and people often add an inline preamp.
+ How do I calculate preamp gain?
Work out the microphone's output voltage at your sound level using its sensitivity, then find the gain that raises it to the input level where your converter sits at your target dBFS. The calculator does this: gain = target level in dBu minus microphone level in dBu.
+ What gain should I set for a podcast?
Set it so your loudest words peak between −12 and −6 dBFS, which puts your normal speaking voice around −18 dBFS. Start with gain low, speak at your normal level and raise it until peaks reach about −10 dBFS.
+ Does moving closer to the mic reduce the gain I need?
Yes. In free space, halving the distance makes the signal about 6 dB louder, so you need 6 dB less gain. It also improves the signal-to-noise ratio by the same amount, which is why distance is the first thing to fix.
+ What is dBFS and what is 0 dBFS in dBu?
dBFS means decibels below digital full scale, the loudest signal a converter can record. The analogue input level that equals 0 dBFS varies by interface, and +18 dBu and +24 dBu are both common. Your interface manual lists it, and you can change the value in the calculator.
Related guides
Go deeper on the ideas behind this calculator.