Understanding gain, noise and file size
A microphone turns air pressure into a tiny electrical signal, often only a few thousandths of a volt. Before a recorder or computer can use it, a preamplifier must raise it by tens of decibels. Too little gain and the recording is buried in noise; too much and it distorts. These calculators show you where the sweet spot is, so you can set gain with confidence rather than trial and error.
Sensitivity: how much signal a mic produces
Sensitivity is stated as millivolts per pascal (mV/Pa). One pascal equals 94 dB SPL, a loud conversation at close range. Condenser microphones commonly produce 10–20 mV/Pa, while dynamic microphones are often 1–3 mV/Pa and therefore need more gain. If your data sheet lists dBV/Pa, divide: −40 dBV/Pa equals 10 mV/Pa.
Distance and loudness
Sound drops by about 6 dB each time the distance doubles. That is why moving closer to the capsule brings so much more signal and why close-talking suits noisy rooms. The calculator takes the loudness measured at one distance and adjusts it to your actual mic distance.
Pressure (Pa) = 10((SPL − 94) ÷ 20)
Mic voltage = sensitivity × pressure
Gain needed
Gain in decibels is 20 times the base-10 logarithm of the ratio between the voltage you want at the preamp output and the voltage the microphone produces. We offer three targets: about 0 dBu for safe recording, +6 dBu for a hotter level and +4 dBu for professional line level. We also show the gain needed for peaks, which are usually 10–15 dB louder than average speech or music.
0 dBu = 0.775 V RMS
Signal-to-noise ratio
The self-noise of a microphone is the quiet hiss it produces even in silence. Subtract it from the 94 dB reference level to get the signal-to-noise ratio. Higher is better: above 74 dB is good, above 80 dB is excellent. A noisy preamp or a noisy room can lower real-world results, so treat this number as the best case.
| Self-noise (dBA) | S/N re 94 dB | Rating |
|---|---|---|
| Under 10 | Over 84 dB | Ultra-quiet |
| 10–16 | 78–84 dB | Excellent |
| 16–20 | 74–78 dB | Good |
| Over 20 | Under 74 dB | Noisy for quiet sources |
Recording storage
Uncompressed audio size is easy to compute: sample rate times bit depth times the number of channels, times the length in seconds. A single hour of 48 kHz, 24-bit mono is around 518 MB. Stereo doubles it, and 96 kHz doubles it again. FLAC compresses losslessly to about 60% of the size on average, while MP3 at 320 kbps is about 144 MB per hour.
Practical tips
- Set gain while the person speaks at their loudest, aiming for peaks around −10 dBFS.
- Use a pop filter and keep a consistent distance; changing it by a few inches shifts the level by several decibels.
- Treat the room before buying a better microphone: noise and reflections hurt more than a small difference in gear.
- Record backup tracks at a safer level when you cannot repeat the performance.