Recording High SPL Sources

High sound pressure level sources challenge recording equipment and technique. Drums, brass instruments, loud guitar amplifiers, and other energetic sources require appropriate microphone selection, signal chain management, and recording approaches to capture clean, undistorted audio.

Understanding High SPL

Sound pressure level measures acoustic energy, expressed in decibels. Conversational speech measures around 60 dB SPL. A drum kit can exceed 120 dB SPL at close range. The difference represents a millionfold increase in acoustic energy.

Microphones convert acoustic pressure to electrical signal. Extreme pressure can exceed a microphone’s ability to track accurately, causing distortion within the microphone before the signal reaches any electronics.

Electronics throughout the signal chain have maximum input and output levels. Exceeding these levels causes clipping and distortion at each affected stage.

Microphone Selection

Dynamic microphones handle high SPL inherently well. Their operating principle tolerates extreme levels without damage or distortion. The Shure SM57 reliably handles close-miked drums and loud guitar amps.

Large-diaphragm condensers vary widely in maximum SPL capability. Some vintage-style designs distort above 120 dB SPL, while modern designs with pad options handle 140 dB or more. Checking specifications before use prevents problems.

Ribbon microphones, despite their delicate reputation for wind sensitivity, handle high SPL well. The velocity-based operating principle accommodates extreme levels. Some ribbons are regularly used on loud sources.

Using Microphone Pads

Condenser microphones often include built-in pad switches, typically offering 10 or 20 dB attenuation. Engaging the pad reduces output level before internal amplification, preventing internal distortion.

Choosing pad setting depends on source level and preamp input headroom. A 10 dB pad suffices for moderately loud sources. Very loud sources like close-miked drums may need 20 dB attenuation.

External inline pads provide attenuation for microphones without built-in switches. These XLR barrel adapters reduce level between microphone and preamp.

Preamp Considerations

Preamp input stages can overload before gain circuits. Even with gain fully reduced, extremely hot signals may distort at the input transformer or buffer stage.

Preamp pad switches reduce signal before the gain stage. Engaging the pad protects input stages from overload on high-level signals.

Quality preamps specify maximum input level. Matching microphone output to preamp capability ensures clean capture. Specifications around +20 dBu input capability suit most microphone applications.

Positioning Strategies

Increasing microphone distance from loud sources reduces level naturally. The inverse square law means doubling distance reduces level by 6 dB.

Off-axis positioning points the microphone’s less sensitive direction toward the loudest portion of the source. The pickup pattern’s natural rejection provides some attenuation.

These physical adjustments change the sound as well as the level. Distance adds room contribution. Off-axis positioning alters frequency response. The adjustments may or may not suit the desired result.

Gain Staging for Loud Sources

Recording level targets should leave substantial headroom. Peaks around -12 dBFS provide safety margin for unexpected transients that loud sources frequently produce.

Conservative initial settings allow gradual increase rather than discovering clipping during takes. Starting with more pad and less gain than expected provides insurance.

Monitoring input meters reveals whether levels remain safe. Peaks occasionally approaching but never reaching 0 dBFS indicate appropriate gain staging.

Protecting Equipment

Ribbon microphone elements can be damaged by extreme blasts of air, though not by high SPL itself. Positioning away from bass drum ports and away from wind prevents ribbon damage.

Ear protection matters when working around loud sources. Extended exposure to levels common in studio environments can cause hearing damage. Monitoring from isolated control rooms or using headphones reduces exposure.

Electronic equipment handles high levels without damage as long as they don’t exceed specifications. Distortion from overload sounds bad but doesn’t typically cause permanent damage.