Simulating Submerged Acoustics in Audio Post-Production

Characteristics of Underwater Sound

Sound propagation in aquatic environments differs significantly from air. Key attributes include:

• Frequency Attenuation: Higher frequencies are rapidly absorbed, resulting in a loss of treble and clarity.
• Speed of Sound: Sound travels faster than in air, but this aspect is less perceptible in typical audiovisual contexts.
• Refraction and Reflection: Sound waves bend (refract) due to changes in density and temperature, causing distortions. Reflection from surfaces (objects, seabed) creates echoes and reverberation.
• Increased Density: Denser mediums like water affect sound propagation differently than air.

Audio Processing Techniques

Achieving a convincing submerged sound effect involves manipulating several audio parameters:

Equalization (EQ)

Apply a low-pass filter to attenuate high frequencies. The cutoff frequency depends on the desired depth and clarity, but a starting point might be between 1-3 kHz. Experiment with shelving filters and high-frequency roll-offs for a natural feel.

Reverberation

Use a reverb plugin with a short decay time and a wet/dry mix that balances intelligibility with the sense of immersion. Adjust the reverb parameters to mimic the acoustic space of an underwater environment, which often includes dense, complex reflections.

Distortion/Saturation

Subtle distortion can simulate the clipping and distortion caused by pressure changes and limitations of underwater recording equipment. Use a mild overdrive or saturation plugin.

Filtering and Resonance

Utilize band-pass filters or resonant peaks to emphasize specific frequency ranges that might be prominent in underwater recordings. Experiment with moving the center frequency of a band-pass filter to create a dynamic filtering effect.

Modulation Effects

Chorus or flanger effects, used sparingly, can introduce subtle phase cancellations that enhance the sense of movement and distortion typically found in aquatic soundscapes. Keep the depth and rate low to avoid excessive artificiality.

Plugin Selection and Parameter Settings

Many digital audio workstations (DAWs) include built-in EQ, reverb, and distortion plugins. Third-party plugins specifically designed for underwater or aquatic effects can offer more specialized and nuanced results. Pay attention to plugin documentation and experiment with parameter settings to achieve the desired sound.

Considerations for Dialogue

Dialogue requires careful treatment. Excessive processing can render it unintelligible. Techniques include:

• Applying a more gentle EQ curve.
• Using a de-esser to reduce sibilance, which can become harsh when high frequencies are attenuated.
• Experimenting with a subtle vocoder to create a slightly robotic or distorted vocal character.

Layering and Sound Design

Combine processed audio with recordings of actual underwater sounds (e.g., bubbles, sonar pings, marine life) to create a rich and believable soundscape. The skillful blend of processing and sound design is critical for a convincing final result.