5.1 Fundamentals of Audio Recording and Editing

Sound waves are the foundation of audio recording. They travel through air, water, and solids as longitudinal waves, with properties like frequency, amplitude, and phase determining how we perceive sound. Understanding these basics is crucial for effective audio recording.

Audio recording equipment transforms sound waves into electrical signals. Microphones, digital recorders, and audio interfaces are essential tools. The recording environment, including room acoustics and background noise, greatly impacts the final sound quality. Mastering these elements is key to capturing great audio.

Sound Wave Properties and Audio Recording

Properties of sound waves

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• Sound waves propagate through a medium (air, water, solids) as longitudinal waves
• Characterized by alternating compression and rarefaction of the medium
• Frequency measured in Hertz (Hz) determines the pitch of the sound
  • Human hearing range spans from 20 Hz to 20 kHz
• Amplitude measured in decibels (dB) determines the loudness of the sound
  • Maximum displacement of the sound wave from its resting position
• Phase represents the position of a point on a waveform cycle relative to the start of the cycle
  • Measured in degrees (0° to 360°) or radians (0 to $2\pi$)
  • Crucial when combining multiple sound sources (mixing, recording with multiple microphones)

Audio recording equipment

• Microphones convert acoustic energy (sound waves) into electrical energy (audio signal)
  • Dynamic, condenser, and ribbon microphones each have unique characteristics and applications
  • Polar patterns (omnidirectional, cardioid, figure-8, shotgun) determine the microphone's sensitivity to sound from different directions
• Digital recorders capture and store audio in digital format
  • Portable devices with built-in microphones and storage (SD cards, internal memory)
  • Support various recording formats (WAV, MP3) and bit depths (16-bit, 24-bit)
• Audio interfaces connect microphones and instruments to a computer
  • Convert analog signals to digital and vice versa
  • Provide preamps, phantom power, and multiple inputs/outputs for flexibility in recording setups

Recording in different environments

• Room acoustics significantly impact the recorded sound
  • Reflections, reverberation, and absorption of sound waves in a space
  • Acoustic treatment (panels, bass traps, diffusers) helps control reflections and improve sound quality
  • Microphone placement is crucial for capturing the desired sound (close miking, distant miking)
• Background noise can interfere with the recording
  • Common sources include HVAC systems, traffic, electrical hum, and unwanted ambient sounds
  • Minimize noise by selecting quiet locations, using noise-canceling microphones, and applying noise reduction techniques in post-production
• Microphone techniques for different situations
  1. Close miking: placing the microphone near the sound source for a direct, isolated sound
  2. Distant miking: placing the microphone farther away to capture room ambiance and a more natural sound
  3. Stereo techniques (X/Y, ORTF, Mid-Side) for capturing a wider, more immersive soundstage

Digital Audio Editing

Digital audio editing techniques

• Non-destructive editing allows for unlimited undo and redo operations without permanently altering original audio files
  • Basic operations include cut, copy, paste, trim, and split
• Fades and crossfades create smooth transitions between audio clips
  • Fade-in: gradual increase in audio level
  • Fade-out: gradual decrease in audio level
  • Crossfades: smooth transition between two audio clips, removing clicks or pops
• Equalization (EQ) adjusts the balance of frequency components in an audio signal
  • Boost or cut specific frequency ranges to shape the sound
  • Parametric, graphic, and shelving EQs offer different levels of control and precision
• Dynamics processing tools control the dynamic range of the audio signal
  • Compressors reduce dynamic range by attenuating loud parts and boosting quiet parts
  • Limiters prevent the audio signal from exceeding a set threshold, preventing clipping and distortion
  • Expanders and gates reduce noise by attenuating signals below a set threshold
• Time-based effects create spatial and depth effects
  • Delay repeats the audio signal after a set time interval, creating echo effects
  • Reverb simulates the natural reverberation of a space, adding depth and dimension to the sound
  • Chorus and flanger create a thickening effect by combining slightly delayed and pitch-modulated copies of the original signal