Matching Microphones and Preamplifiers
"Impedance Matching" in the context of microphones and preamplifiers is often misunderstood. Most microphones and preamps work well together without needing precise impedance matching. The topic gains significance only when seeking specific tonal qualities, coloration, or characteristics.
Before delving deeper, let's define impedance. Every microphone has an output impedance, and every preamp has an input impedance. Impedance (Z) represents the resistance encountered by the signal current flowing from the mic circuit into the preamp circuit.
The term "Hi-Z" (High Impedance) describes such interfaces (familiar to guitarists). Crucially, the preamp's input impedance significantly impacts the sound. The interaction between the mic's output impedance and the preamp's input impedance alters the final signal, affecting aspects like EQ balance and transient response. Different preamp input impedances interact uniquely with different mic output impedances.
Analogy: Imagine a garden hose (mic = low-impedance source, low water resistance) and a nozzle (preamp = high impedance). Closing the nozzle valve (high input impedance) maximizes pressure (voltage) but stops flow (current=0).
Slightly opening the valve reduces impedance and pressure (though still high), allowing flow but creating a hiss (high frequencies). Further opening lowers impedance and pressure, increases flow, and reduces hiss. Thus, lower preamp impedance attenuates high frequencies.
Matching mic and preamp impedances directly is incorrect, reducing signal level and signal-to-noise ratio by 6dB. For dynamic and condenser mics, the optimal preamp input impedance is roughly 10 times the mic's output impedance. Modern preamps with adjustable input impedance (e.g., Focusrite ISA 428, Summit 2BA-221) offer flexibility. Their transformer levels and interaction with mic impedance are adjustable, enabling various tonal colorations via the EQ effects mentioned.
Key advantages: Achieve desired frequency adjustments during recording without adding EQ units to the signal path, avoiding noise and signal loss. Beyond the 10:1 rule, safely experiment with input impedance settings to find the preferred sound.
Before delving deeper, let's define impedance. Every microphone has an output impedance, and every preamp has an input impedance. Impedance (Z) represents the resistance encountered by the signal current flowing from the mic circuit into the preamp circuit.
The term "Hi-Z" (High Impedance) describes such interfaces (familiar to guitarists). Crucially, the preamp's input impedance significantly impacts the sound. The interaction between the mic's output impedance and the preamp's input impedance alters the final signal, affecting aspects like EQ balance and transient response. Different preamp input impedances interact uniquely with different mic output impedances.
Analogy: Imagine a garden hose (mic = low-impedance source, low water resistance) and a nozzle (preamp = high impedance). Closing the nozzle valve (high input impedance) maximizes pressure (voltage) but stops flow (current=0).
Slightly opening the valve reduces impedance and pressure (though still high), allowing flow but creating a hiss (high frequencies). Further opening lowers impedance and pressure, increases flow, and reduces hiss. Thus, lower preamp impedance attenuates high frequencies.
Matching mic and preamp impedances directly is incorrect, reducing signal level and signal-to-noise ratio by 6dB. For dynamic and condenser mics, the optimal preamp input impedance is roughly 10 times the mic's output impedance. Modern preamps with adjustable input impedance (e.g., Focusrite ISA 428, Summit 2BA-221) offer flexibility. Their transformer levels and interaction with mic impedance are adjustable, enabling various tonal colorations via the EQ effects mentioned.
Key advantages: Achieve desired frequency adjustments during recording without adding EQ units to the signal path, avoiding noise and signal loss. Beyond the 10:1 rule, safely experiment with input impedance settings to find the preferred sound.