Sound & Recording Ears, Physics, Acoustics, Microphones and Digital Recording

EARS  Difference between Hearing and Vision.  Ear safety.  Ear training.

Hearing vs. Vision  Difference between Hearing and Vision. Hearing is omnidirectional, vision is directional. Hearing is omnidirectional, vision is directional. You can hear perceive sound emanating from behind your head.You can hear perceive sound emanating from behind your head. You can only see what you are looking at directly.You can only see what you are looking at directly. Sound can be layered, vision can not. Sound can be layered, vision can not. To a bass line, you can add drums, vocals, guitar, etc. and still hear it all.To a bass line, you can add drums, vocals, guitar, etc. and still hear it all. If I walk in front of you, you won’t be seen anymore.If I walk in front of you, you won’t be seen anymore.

Natural Ear Protection  Ossicles (three bones) in middle ear adjust to protect inner ear from extreme pressure. Takes 1/10 th of a second for ossicles to adjust. Takes 1/10 th of a second for ossicles to adjust. No protection against sudden loud sounds. No protection against sudden loud sounds. Can not adjust enough to deal with extremely loud sound. Can not adjust enough to deal with extremely loud sound.

Hearing Damage  Continued exposure to high sound- pressure levels (SPLs) damages receptive fibers in cochlea. Mid-high frequencies go first – important for understanding speech. Mid-high frequencies go first – important for understanding speech. Cotton ears: Temporary Threshold Shift (TTS). Ears shut down to protect themselves. Cotton ears: Temporary Threshold Shift (TTS). Ears shut down to protect themselves. Ringing ears: Tinnitus. Sign of possible permanent damage. Ringing ears: Tinnitus. Sign of possible permanent damage. Hearing loss affects 1 in 9. Progressive. Hearing loss affects 1 in 9. Progressive.

Physiological Damage  Loud sounds cause adverse physiological effects: Increases heart rate. Increases heart rate. Raises blood pressure. Raises blood pressure. Contracts blood vessels and muscles. Contracts blood vessels and muscles. Releases stress hormones. Releases stress hormones. Disrupts digestive functions. Disrupts digestive functions. Causes anxiety and fatigue. Causes anxiety and fatigue.

Ear Training  Paying attention to sound: Layers – selective listening. Layers – selective listening. Content. Content. Function. Function. Direction Direction Characteristics Characteristics

Physics and Psychophysics  Sound waves.  Frequency.  Amplitude.  Timbre.  Envelope.

Sound Waves  Created by object vibrating in an elastic medium - causing changes in pressure (number of molecules bunched together). Outward movement – compression. Outward movement – compression. Inward movement – rarefaction. Inward movement – rarefaction.

Frequency  Number of cycles (compression/rarefaction) per second. Expressed in Hertz (Hz) and Kilohertz (kHz). Expressed in Hertz (Hz) and Kilohertz (kHz). Higher frequency – higher pitch. Higher frequency – higher pitch. Bass: Hz.Bass: Hz. Mid-range: 320-5,120 Hz.Mid-range: 320-5,120 Hz. Treble: 5,120-20,000 Hz.Treble: 5,120-20,000 Hz. Extreme highs and lows are “sensed,” not heard.Extreme highs and lows are “sensed,” not heard.

Amplitude  Number of molecules in motion – higher pressure, higher volume. Measured in decibels (dB). Measured in decibels (dB). 20 dB – whisper.20 dB – whisper. 60 dB – talking.60 dB – talking. 80 dB – yelling.80 dB – yelling.  Equal Loudness Principle. Human ear is more responsive to midrange than bass and treble. Human ear is more responsive to midrange than bass and treble. At higher levels, bass and treble need boost to sound the same. At higher levels, bass and treble need boost to sound the same.  Masking. Louder sounds mask softer sounds. Louder sounds mask softer sounds. Taken advantage of in audio compression – perceptual noise shaping. Taken advantage of in audio compression – perceptual noise shaping.

Timbre  Gives tonal quality – difference between instruments or voices. Fundamental (pure) tone – Doesn’t exist in nature. Fundamental (pure) tone – Doesn’t exist in nature. Overtones – other tones riding along with pure tone. Overtones – other tones riding along with pure tone. Harmonics: exact multiples of fundamental tone (For example: 4, 6, 8, 10 kHz are harmonics of 2 kHz).Harmonics: exact multiples of fundamental tone (For example: 4, 6, 8, 10 kHz are harmonics of 2 kHz). Other overtones – non-harmonic.Other overtones – non-harmonic.

Envelope  Attack Amount of time it takes a tone to reach maximum volume. Amount of time it takes a tone to reach maximum volume.  Decay Amount of time it takes a tone to decrease from max to sustained volume. Amount of time it takes a tone to decrease from max to sustained volume.  Sustain Amount of time a tone stays at a constant volume. Amount of time a tone stays at a constant volume.  Release Amount of time it takes for a tone to end. Amount of time it takes for a tone to end.

Acoustics  Reflections.  Acoustic choices.  Noise.

Reflections  Direct sound. Sound waves coming directly off of sound source. Sound waves coming directly off of sound source.  Reflections – off of other objects, walls, etc. Early reflections. Early reflections. Increase loudness – give impression of size of environment.Increase loudness – give impression of size of environment. Later reflections. Later reflections. Echo – distinct, single reflection.Echo – distinct, single reflection. Reverb – reflections of reflections – flutter echos.Reverb – reflections of reflections – flutter echos.  Room shapes and materials. Consistently shaped rooms can cause unwanted effects. Consistently shaped rooms can cause unwanted effects. Complex shapes disperse reflections more effectively. Complex shapes disperse reflections more effectively. Materials such as carpet and concrete absorb and reflect sound differently. Materials such as carpet and concrete absorb and reflect sound differently.

Acoustic Choices  So what kind of space is best to record in? Depends on what you’re recording. Depends on what you’re recording. Orchestral is good with reverb, combining various instruments on the sonic palette – live or wet room.Orchestral is good with reverb, combining various instruments on the sonic palette – live or wet room. Rock needs less reverb to hear specific instruments more distinctly – medium room.Rock needs less reverb to hear specific instruments more distinctly – medium room. Vocal needs little reverb – dead or dry room.Vocal needs little reverb – dead or dry room. But there is no hard and fast rule – it’s a matter of taste.But there is no hard and fast rule – it’s a matter of taste. Reverberation can be added in postproduction with signal processing – but may not be as rich.Reverberation can be added in postproduction with signal processing – but may not be as rich.

Noise  Noise is everywhere. If it’s quiet enough we can even hear our own blood flowing through our veins – so we never can really hear complete silence. If it’s quiet enough we can even hear our own blood flowing through our veins – so we never can really hear complete silence. Unwanted noise can be minimized with isolation. Unwanted noise can be minimized with isolation. Keeps unwanted sounds from getting in.Keeps unwanted sounds from getting in. Stops loud noises from disturbing others.Stops loud noises from disturbing others.

Microphones  Types  Performance  Pickup Patterns  Special Use

Types  All microphones are transducers. Convert one type of energy to another – acoustic to electric (speakers other way). Convert one type of energy to another – acoustic to electric (speakers other way).  Dynamic Magnetic induction. Doesn’t need power, less expensive. Magnetic induction. Doesn’t need power, less expensive. Moving coil – most common and durable. Moving coil – most common and durable. Ribbon – less common, more fragile. Ribbon – less common, more fragile.  Condenser (capacitor) Variable capacitance. Needs power. Variable capacitance. Needs power. Diaphragm and charged fixed plate. Diaphragm and charged fixed plate.

Performance  Each microphone is different. Different frequency response. Different frequency response. Less mass of element, more responsive. Less mass of element, more responsive. Condensers often have less mass.Condensers often have less mass. Less responsive does not mean better.Less responsive does not mean better. As with all audio – it depends on what you are recording and what effect you want.As with all audio – it depends on what you are recording and what effect you want.  Wind screens and pop filters. Reduce pop from syllibants. Reduce pop from syllibants. Reduce wind sound. Reduce wind sound.

Pickup Patterns  Omnidirectional Picks up sound more consistently from all directions. Picks up sound more consistently from all directions.  Cardioid (unidirectional) Picks up sound mostly from the front. Picks up sound mostly from the front. Heart-shaped (cardiac) pattern. Heart-shaped (cardiac) pattern. Proximity effect. Proximity effect. Picks up more bass close-up.Picks up more bass close-up. Bass roll-off switch to compensate.Bass roll-off switch to compensate. Super, Hyper: more directed pattern. Super, Hyper: more directed pattern.  Bidirectional Picks up from sides best. Picks up from sides best.

Special Use  System Mic Interchangeable heads for different pick up patterns. Interchangeable heads for different pick up patterns.  Stereophonic. Two elements – right and left. Two elements – right and left. Binaural – recreates human head, but must be listened to on headphones, so not commercially viable. Binaural – recreates human head, but must be listened to on headphones, so not commercially viable.  Surround sound. 5.1 sound recorded on one multi-element mic or several separate mics. 5.1 sound recorded on one multi-element mic or several separate mics.  Other: Lavalier – miniature for video or film. Lavalier – miniature for video or film. Shotgun – attenuates all but front, compresses distances. Shotgun – attenuates all but front, compresses distances. Parabolic – captures over long distances, lots of noise. Parabolic – captures over long distances, lots of noise. Adaptive Array – cancels unwanted sound digitally. Adaptive Array – cancels unwanted sound digitally.

Digital Audio Recording Process  Sample  Quantize  Code

Step 1: Sample  Snapshot of wave’s amplitude.  Samples “plot” the waveform.  Two samples required to form a cycle. CD-quality samples at 44.1KHz, since upper limit of human hearing is 20KHz. CD-quality samples at 44.1KHz, since upper limit of human hearing is 20KHz. Low rate cuts high frequencies. Low rate cuts high frequencies.

Step 2: Quantize  Sample snapshots may be at infinite points.  Must limit the number of choices and round to closest.  1-bit is either “on” or “off”.  Each additional bit doubles possibilities.  CD-quality is 16-bit, which allows for 65,536 possibilities.  Higher bit-depth - higher signal-to-noise ratio – more signal, less noise.

Step 3: Coding  Takes the quantized sample and assigns it a binary code.  A CD-quality sample, being 16-bit, would have 16 zeros or ones per sample. For example: For example:

Digital Audio Quality vs. File Size Considerations  Stereo or Mono Halves file size without reducing quality. Halves file size without reducing quality. Reduces presence, sound placing. Reduces presence, sound placing.  Lower Sample Rate Cuts higher frequencies. Cuts higher frequencies.  Lower Bit-Depth Decreases signal-to-noise ratio. Decreases signal-to-noise ratio. Noise especially obvious with quieter signal. Noise especially obvious with quieter signal.  Compression CODECs are another subject for another test.