Knowledge on Microphone and Mixer Levels
Microphone specifications are vital for selection and application. Comprehending them enables optimal mic-source distance management, accurate sound pressure-to-voltage conversion, and precise calibration of the sound field's SPL to the mixer input level. This determines the mixer's input gain for the highest signal-to-noise ratio and lowest distortion.
Which mic specs are mixer-relevant, and how do they determine the mixer's operating level?
I. Key Specifications
Audio applications provide comprehensive information on MIDI, recording, mixing, music production, recording, audio, VST, mixing, instruments, guitars, microphones, headphones, sound cards, and more!
Broadcast-grade mics have nearly 10 specs; the most critical for the source and mixer are: Maximum Input SPL, Sensitivity, and Maximum Output Level. Maximum Input SPL defines the SPL causing 0.5% THD, with the relation:
0dB SPL = 2×10⁻⁵ Pa
Professional mics typically have high max input SPL. With proper distance, audible distortion is avoided. We focus on Sensitivity and Max Output Level, which directly affect mixer level.
1. Sensitivity
Sensitivity is the output voltage per unit input sound pressure (mV/Pa). For consistency with circuit level measurement, it's also expressed in dB. Early dB units included dBm and dBV:
0dBm = 1mW/Pa (1Pa input producing 1mW into 600Ω = 0dB)
0dBV = 1V/μbar (1μbar input producing 1V = 0dB).
Modern units use dBμ:
0dBμ = 0.775V/Pa (1Pa input producing 0.775V = 0dB).
Convert any sensitivity to dBμ using Pa as the reference.
Example: NEUMANN U89 sensitivity = 8mV/Pa. Convert:
20lg[(0.008V/Pa) ÷ (0.775V/Pa)] ≈ -40dBμ.
Another: AKG C414 sensitivity = -60dBV.
Since 0dBV = 1V/μbar = 10V/Pa,
Find output X at 1Pa for -60dBV:
20lg[(X V/Pa) ÷ (10V/Pa)] = -60 → X = 0.01V (10mV/Pa).
Then: 20lg[(0.01V/Pa) ÷ (0.775V/Pa)] ≈ -37dBμ.
2. Maximum Output Level
This is the output level at the mic's max input SPL. Like max SPL governs distance, max output level directly sets the mixer's input operating level. Given sensitivity and max SPL, max output is calculable.
NEUMANN U89 again: Sensitivity 8mV/Pa, Max Input SPL 134dB SPL (with -10dB pad). Convert SPL to pressure:
134dB SPL = 20lg(X / 2×10⁻⁵ Pa) → X = 100Pa.
Output = 100Pa × 8mV/Pa = 800mV.
Level = 20lg[(0.8V/Pa) ÷ (0.775V/Pa)] ≈ 0dBμ (theoretical max).
Normally, the -10dB pad isn't used (to minimize noise), so max SPL rarely exceeds 124dB SPL (normal mode), keeping max output well below 0dBμ.
II. Setting Mixer Operating Level
Technically, the mixer's operating level ensures its maximum signal doesn't exceed the manufacturer's headroom limit (program needs also dictate level). Headroom is the level range above 0dBμ before THD limits.
Knowing the source's max SPL at the mic and the mic's sensitivity allows calculation of max output level. The difference between this level and the mixer's headroom limit sets the input gain (mic preamp gain); the resulting signal level is the mixer's operating level.
Example: Soprano voice, U89 mic, AMEK RemBandt mixer. Max SPL at 70cm = 112dB SPL (peak, A-wtd). U89 max SPL = 124dB, Sensitivity 8mV/Pa.
112dB SPL = 20lg(X / 2×10⁻⁵) → X = 8Pa.
Output = 8Pa × 8mV/Pa = 64mV → Level = 20lg(0.064 / 0.775) ≈ -22dBμ.
Connecting to a mixer with 70dB mic preamp gain and 12dBμ headroom (THD=0.017%), the headroom margin is +12dBμ - (-22dBμ) = 34dB. This 34dB sets the required input gain, defining the operating level.
In practice, reduce gain slightly to ensure THD < 0.017% at peak. Set channel, monitor, and master faders to 0dB. Observe input/output meters; adjust gain so levels stay nominal.
Which mic specs are mixer-relevant, and how do they determine the mixer's operating level?
I. Key Specifications
Audio applications provide comprehensive information on MIDI, recording, mixing, music production, recording, audio, VST, mixing, instruments, guitars, microphones, headphones, sound cards, and more!
Broadcast-grade mics have nearly 10 specs; the most critical for the source and mixer are: Maximum Input SPL, Sensitivity, and Maximum Output Level. Maximum Input SPL defines the SPL causing 0.5% THD, with the relation:
0dB SPL = 2×10⁻⁵ Pa
Professional mics typically have high max input SPL. With proper distance, audible distortion is avoided. We focus on Sensitivity and Max Output Level, which directly affect mixer level.
1. Sensitivity
Sensitivity is the output voltage per unit input sound pressure (mV/Pa). For consistency with circuit level measurement, it's also expressed in dB. Early dB units included dBm and dBV:
0dBm = 1mW/Pa (1Pa input producing 1mW into 600Ω = 0dB)
0dBV = 1V/μbar (1μbar input producing 1V = 0dB).
Modern units use dBμ:
0dBμ = 0.775V/Pa (1Pa input producing 0.775V = 0dB).
Convert any sensitivity to dBμ using Pa as the reference.
Example: NEUMANN U89 sensitivity = 8mV/Pa. Convert:
20lg[(0.008V/Pa) ÷ (0.775V/Pa)] ≈ -40dBμ.
Another: AKG C414 sensitivity = -60dBV.
Since 0dBV = 1V/μbar = 10V/Pa,
Find output X at 1Pa for -60dBV:
20lg[(X V/Pa) ÷ (10V/Pa)] = -60 → X = 0.01V (10mV/Pa).
Then: 20lg[(0.01V/Pa) ÷ (0.775V/Pa)] ≈ -37dBμ.
2. Maximum Output Level
This is the output level at the mic's max input SPL. Like max SPL governs distance, max output level directly sets the mixer's input operating level. Given sensitivity and max SPL, max output is calculable.
NEUMANN U89 again: Sensitivity 8mV/Pa, Max Input SPL 134dB SPL (with -10dB pad). Convert SPL to pressure:
134dB SPL = 20lg(X / 2×10⁻⁵ Pa) → X = 100Pa.
Output = 100Pa × 8mV/Pa = 800mV.
Level = 20lg[(0.8V/Pa) ÷ (0.775V/Pa)] ≈ 0dBμ (theoretical max).
Normally, the -10dB pad isn't used (to minimize noise), so max SPL rarely exceeds 124dB SPL (normal mode), keeping max output well below 0dBμ.
II. Setting Mixer Operating Level
Technically, the mixer's operating level ensures its maximum signal doesn't exceed the manufacturer's headroom limit (program needs also dictate level). Headroom is the level range above 0dBμ before THD limits.
Knowing the source's max SPL at the mic and the mic's sensitivity allows calculation of max output level. The difference between this level and the mixer's headroom limit sets the input gain (mic preamp gain); the resulting signal level is the mixer's operating level.
Example: Soprano voice, U89 mic, AMEK RemBandt mixer. Max SPL at 70cm = 112dB SPL (peak, A-wtd). U89 max SPL = 124dB, Sensitivity 8mV/Pa.
112dB SPL = 20lg(X / 2×10⁻⁵) → X = 8Pa.
Output = 8Pa × 8mV/Pa = 64mV → Level = 20lg(0.064 / 0.775) ≈ -22dBμ.
Connecting to a mixer with 70dB mic preamp gain and 12dBμ headroom (THD=0.017%), the headroom margin is +12dBμ - (-22dBμ) = 34dB. This 34dB sets the required input gain, defining the operating level.
In practice, reduce gain slightly to ensure THD < 0.017% at peak. Set channel, monitor, and master faders to 0dB. Observe input/output meters; adjust gain so levels stay nominal.