🔊Sound Design Unit 6 – Microphone Types and Recording Techniques

Microphone Basics

• Microphones convert acoustic energy (sound waves) into electrical energy (audio signals)
• Consist of a diaphragm that vibrates in response to sound pressure, generating an electrical current
• Transducer types include dynamic, condenser, and ribbon microphones
  • Dynamic microphones use a moving coil attached to the diaphragm (Shure SM57)
  • Condenser microphones use a thin, electrically-charged diaphragm and backplate (Neumann U87)
  • Ribbon microphones use a thin metal ribbon suspended between two magnets (Royer R-121)
• Microphone sensitivity measures the output voltage for a given sound pressure level (SPL)
• Impedance refers to the microphone's resistance to alternating current (AC) flow
  • Low-impedance microphones (150-600 ohms) are less susceptible to interference and signal loss
  • High-impedance microphones (10,000 ohms or more) require a preamp close to the microphone

Types of Microphones

• Dynamic microphones are rugged, affordable, and well-suited for high SPL sources (drums, guitar amps)
• Condenser microphones offer high sensitivity, wide frequency response, and excellent transient response
  • Require phantom power (48V) to operate the internal preamp
  • Well-suited for capturing detailed, nuanced sounds (vocals, acoustic instruments)
• Ribbon microphones provide a smooth, natural sound with a figure-8 polar pattern
  • Fragile and sensitive to high SPL, best used in controlled studio environments
• USB microphones integrate the microphone, preamp, and analog-to-digital converter into a single unit
  • Convenient for podcasting, voiceovers, and home recording
• Lavalier microphones are small, clip-on microphones designed for hands-free speech capture
  • Commonly used in television, theater, and public speaking

Polar Patterns and Directionality

• Polar patterns describe a microphone's sensitivity to sound from different directions
• Omnidirectional microphones capture sound equally from all directions (360 degrees)
  • Ideal for capturing room ambience or multiple sound sources
• Cardioid microphones are most sensitive to sound directly in front, with reduced sensitivity on the sides and rear
  • Provides good isolation and feedback rejection, suitable for most recording applications
• Figure-8 (bi-directional) microphones are equally sensitive to sound from the front and rear, with minimal pickup on the sides
  • Often used for stereo recording techniques (Mid-Side, Blumlein)
• Supercardioid and hypercardioid microphones have a narrower frontal pickup and increased rear sensitivity compared to cardioid
  • Provide high directionality and isolation, useful in noisy environments or for spot miking
• Shotgun microphones have an extremely narrow, directional pickup pattern
  • Commonly used in film and video production for capturing dialogue or sound effects at a distance

Frequency Response and Sensitivity

• Frequency response describes a microphone's ability to capture different frequencies of sound
  • Measured in Hertz (Hz), with the audible range spanning 20 Hz to 20 kHz
• Flat frequency response indicates equal sensitivity across the frequency spectrum
  • Ideal for accurate, uncolored sound reproduction (measurement microphones)
• Shaped frequency response emphasizes or attenuates specific frequency ranges
  • Enhances certain characteristics of the sound source or compensates for proximity effect
• Proximity effect is an increase in low-frequency response when a directional microphone is close to the sound source
  • Can be used creatively to add warmth and depth to a recording (close-miking vocals or instruments)
• Sensitivity refers to the microphone's output level for a given sound pressure level (SPL)
  • Higher sensitivity microphones require less preamp gain, reducing noise
  • Lower sensitivity microphones can handle higher SPLs without distortion

Microphone Placement Techniques

• Close miking involves placing the microphone within a few inches of the sound source
  • Provides high isolation, reduced room ambience, and increased bass response due to proximity effect
  • Suitable for capturing individual instruments or vocals in a multi-track recording
• Distant miking places the microphone several feet away from the sound source
  • Captures more room ambience and natural sound, with less isolation
  • Often used for recording ensembles, choirs, or room sounds
• Stereo miking techniques use multiple microphones to capture the spatial characteristics of a sound source
  • XY technique: Two cardioid microphones at 90-degree angles, providing a wide stereo image
  • ORTF technique: Two cardioid microphones spaced 17cm apart at a 110-degree angle, mimicking human ear spacing
  • Mid-Side (MS) technique: A cardioid (Mid) and figure-8 (Side) microphone, allowing stereo width adjustment in post-production
• Spot miking involves using multiple microphones to capture individual sound sources within an ensemble
  • Allows for greater control and isolation of each source during mixing
• Room miking places microphones to capture the overall sound of the room or acoustic space
  • Can be used to add natural reverb or ambience to a recording

Recording Environments and Acoustics

• Acoustic treatment controls the reflection, absorption, and diffusion of sound within a space
  • Absorption materials (foam, fiberglass) reduce reflections and reverberation time
  • Diffusion materials (wood, polycylindrical diffusers) scatter sound waves, minimizing distinct echoes
• Soundproofing isolates the recording space from external noise and prevents sound from leaking out
  • Uses dense, massive materials (concrete, double-wall construction) to block sound transmission
• Room modes are standing waves that occur at specific frequencies, determined by the room's dimensions
  • Can cause uneven frequency response and coloration of the recorded sound
  • Addressed through proper room design, acoustic treatment, and strategic microphone placement
• Reverberation is the persistence of sound in a space after the original sound has stopped
  • Characterized by the reverberation time (RT60), the time it takes for sound to decay by 60 dB
  • Controlled through acoustic treatment and microphone placement
• Ambient noise is the background noise present in a recording environment
  • Includes HVAC systems, electrical hum, and external traffic or construction noise
  • Minimized through soundproofing, acoustic treatment, and noise reduction techniques (e.g., noise gates)

Signal Processing and Effects

• Preamplification boosts the low-level microphone signal to line level for further processing or recording
  • Microphone preamps can add coloration and character to the sound
• Equalization (EQ) adjusts the balance of frequencies in the audio signal
  • Used to correct problems, enhance desired frequencies, or creatively shape the sound
• Compression reduces the dynamic range of the audio signal by attenuating loud parts and boosting quiet parts
  • Helps to maintain consistent levels, increase perceived loudness, and control peaks
• Limiting is a form of extreme compression that prevents the signal from exceeding a set threshold
  • Used to protect equipment from overload and ensure compliance with broadcast standards
• Reverb and delay effects simulate the natural reflections and echoes of a space
  • Can add depth, dimension, and a sense of space to a recording
  • Digital reverb and delay plugins offer a wide range of customizable parameters
• Noise reduction techniques help to minimize unwanted noise in a recording
  • Noise gates mute the signal when it falls below a set threshold, reducing background noise
  • Spectral editing allows for the precise removal of specific frequencies or noise components

Practical Recording Scenarios

• Vocal recording requires a quiet environment, a pop filter to reduce plosives, and proper microphone placement
  • Cardioid condenser microphones are often preferred for their detail and clarity
  • Experiment with distance and axis to find the sweet spot and minimize sibilance or proximity effect
• Acoustic guitar recording can use a combination of close and distant miking techniques
  • A small-diaphragm condenser near the 12th fret captures the attack and string detail
  • A large-diaphragm condenser aimed at the body captures the warmth and fullness
• Drum kit recording involves multiple microphones to capture each element of the kit
  • Kick drum: Dynamic mic (e.g., AKG D112) inside the drum, near the beater
  • Snare drum: Dynamic mic (e.g., Shure SM57) aimed at the center of the head, 1-2 inches away
  • Toms: Dynamic mics (e.g., Sennheiser MD 421) aimed at each drum head
  • Overhead mics: Matched pair of condenser mics (e.g., AKG C414) in a stereo configuration above the kit
  • Room mics: Condenser mics (e.g., Neumann U87) placed to capture the overall sound of the room
• Orchestral recording requires careful microphone selection and placement to capture the balance and depth of the ensemble
  • Main stereo pair (e.g., Schoeps MK 4) in a Decca Tree or spaced omni configuration for overall balance
  • Spot mics for individual sections or soloists, using cardioid or supercardioid patterns for isolation
  • Room mics placed further back to capture the natural ambience and reverberation of the hall
• Field recording involves capturing sound effects, ambiences, and environments outside the studio
  • Portable, battery-powered recorders (e.g., Zoom H6) with built-in or external microphones
  • Shotgun microphones (e.g., Sennheiser MKH 416) for directional pickup and isolation
  • Binaural microphones (e.g., Neumann KU 100) for immersive, 3D audio recordings
  • Wind protection (e.g., furry windscreens) and shock mounts to minimize handling noise and vibrations