INFRASOUND, AUDITORY DRIVING, AND NONLINEAR SOUND IN HORROR FILM SOUND EFFECTS

CURTIS B MACINTYRE Table of Contents

1. Introduction 1

2. Infrasound 2 Paranormal Phenomena 2 Infrasonics Concert 3 Subwoofers 4 Infrasound and Missing Fundamentals 4 Infrasound in Film 5 Conclusion 6

3. Auditory Driving 7 Brainwave Entrainment 7 Auditory Brainwave Entrainment 7 Beats 8 Isochronic Tones 9 Entrainment in Music & Film 9 Conclusions 10

4. Nonlinear Sound 11 Vestigial Reflex Response 11 Dissonance 12 Loudness, Surround, and Increased Pitch 12 Nonlinear Sound in Film & Music 12 Conclusions 13

5. Infrasound in Sound Effects 14

6. Auditory Driving in Sound Effects 16 Amplitude Modulation 16 Monaural Beats 16 Delay Units 16 Grids 16

7. Nonlinear Sound in Sound Effects 18 Distortion 18 Inharmonic Sidebands 19 Frequency Shifts 20

8. Analysis 22 a. Infrasound 22 b. Auditory Driving 22 c. Nonlinear Sound 23

9. Conclusions 26

10. Recommended Reading 27 Curtis B. MacIntyre Infrasound, Auditory Driving, and Nonlinear Sound in Horror Film Sound Effects

1. Introduction

“Sound is a very special modality. We cannot handle it. We cannot push it away. We cannot turn our backs to it. We can close our eyes, hold our noses, withdraw from touch, refuse to taste. We cannot close our ears, though we can partly muffle them. Sound is the least controllable of all sense modalities…to hear is actually a kind of obedience.”

Julian Jaynes

Some horror films cause stronger feelings of fear in viewers than others, but how much of those feelings are a result of sound, and can auditory techniques be used to get a stronger fear reaction from an audience? Research and testing was done on the effects of infrasound, auditory driving, and nonlinear sound on listeners, and it was found that these phenomena can affect people emotionally and psychologically.

Some people might ask why somebody would want to develop techniques to scare people, and the answer is simple: many people enjoy being scared. Roller coasters, allegedly haunted houses, and horror films provide a kind of “fun fear” experience for people during which no harm will come to them, but these experiences can provide an enjoyable means to make people feel as though they may be in danger.

This book is divided into two sections. The first section details research into the causes and effects of infrasound, nonlinear sound, and beta brainwave entrainment through auditory driving. The second section details techniques for designing sound effects in Apple’s Logic software using Logic and third party plug-ins, as well as a critical analysis of the techniques used.

It is hoped that this information and these techniques be used by other sound effects designers in their work to assist in providing an enjoyable and involving experience for film audiences.

Comments, questions, and correspondence is welcome and can be directed to www.cbmacintyre.com or [email protected].

Curtis B. MacIntyre

1 Curtis B. MacIntyre Infrasound, Auditory Driving, and Nonlinear Sound in Horror Film Sound Effects

2. Infrasound

The frequency range of human hearing is largely considered to be 20 Hz to 20 kHz, but it is possible for humans to hear and be affected by frequencies below 20 Hz. Frequencies below the threshold of human hearing are known as infrasonic frequencies. Common natural sources of infrasound are thunder, earthquakes, ocean waves, tornados, wind, machinery engines, ventilating systems, and slow speed fans. Exposure to infrasonic frequencies can cause nausea, respiratory problems, decreased mood, sensations of fear, and mild visual hallucinations.

It is a common misconception that infrasound isn’t heard but rather felt through the body, but infrasonic frequencies aren’t any more likely to cause physical sensations than other frequencies at a similar amplitude. While infrasonic frequencies at a high enough amplitude can cause physical sensations, exposure to frequencies between 80 Hz and 100 Hz above 80dB can result in a resonant vibration of the chest of the listener. Tests on deaf subjects have shown that they are able to perceive frequencies below 63 Hz through their bodies at a threshold of 40 to 50 dB higher than those with normal hearing, and about 100 dB higher at 1 kHz.

At a high enough sound pressure level (SPL), tests have shown the ear to register sounds down to 4 Hz in an isolated room, and 1.5 Hz through headphones, although there is a steep increase in the threshold below 50Hz. While the SPL necessary to perceive a 10 phon sound at 1 kHz is 10 dB SPL, a 20 Hz signal requires an approximate SPL of 84 dB SPL and as frequency decreases, the necessary SPL for perception continually and rapidly increases.

Paranormal Phenomena

While working for a company that produced medical equipment Vic Tandy and his associates would frequently experience depression, cold chills, and other unusual phenomena in their laboratory. One evening, Tandy was working in the lab alone and on top of the usual strange sensations, he had a distinct feeling that someone was in the room with him, followed by peripheral visual hallucinations of a silent gray figure moving as a person would to his left.

Later, while doing repairs on a fencing blade, Tandy noticed the blade quickly vibrating in a vice. Presuming that the blade was receiving energy at its resonant frequency, he deduced that the vibration was caused by sound waves in the room. Tandy slowly moved the vice from one side of the room to the other, and observed that the vibration increased as the blade reached the centre of the room, and decreased as it approached the walls. It appeared that the vibration was caused by a standing wave in the room. Because the vibration was strongest in the centre of the room, Tandy presumed that the wave was reflecting off of the walls and reinforcing itself in the centre of the room.

The laboratory was 30ft by 10ft with closed doors and windows on either side. If the speed of sound in this room was 1139 feet per second, and the wavelength was 60 feet (twice the length of the room) the frequency of the standing wave would be 18.98 Hz.

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f = v / λ

f = 1139/60

f=18.98 Hz

Frequency = velocity (1139’ per second) divided by wavelength (60’) The wave was caused by a new fan system that had been installed on one side of the lab. When the fan was turned off, the standing wave disappeared. Shortly after this discovery, modifications were made to the system, and the vibrations and unsettling phenomena ceased.

Tandy later investigated a 14th century cellar at the Tourist Information Centre near Coventry University where numerous people had reported experiencing what they believed to be a haunting. Patrons of the centre reported feeling chills, feeling ill, having visual hallucinations, and feeling a presence upon entering the room. Tandy recorded the ambient sound in the cellar and performed a Fast Fourier Transform (FFT) on it, showing an approximate 19 Hz tone at 38 dB, which was significantly louder than any background sound. Several other samples were taken over a three-hour period, with the same results each time.

The unusual sensations felt in the cellar usually happened at the entrance. The length of the hallway leading into the cellar was approximately 9.5 meters long, which would result in a standing wave at approximately 18 Hz at the entrance. While the experimenters were able to verify the presence of infrasonic frequencies, they were unable to find the source of the wave. When the heating system at the Tourist Centre was turned off, the 18 Hz wave remained present.

According to Infrasound and Low Frequency Vibration by W. Tempest, exposure to frequencies between 15 Hz to 20 Hz can cause “persistent eye watering, respiratory difficulties, and sensations of fear including excessive perspiration and shivering.” A study done by the Aerospace Medical Research Laboratory to find the effects of vibration on the eye and sight found that 11 out of 15 subjects showed maximum resonance of the eye at around 18 Hz, with two subjects slightly higher and two slightly lower. The presence of a frequency close to this could explain the visual hallucinations experienced by Tandy, his co-workers, and visitors to the information centre.

Infrasonic Concert

On May 31 2003 a concert was held at the Purcell Room in London to test the effects of a 17 Hz tone on an audience. Called Infrasonic, the concert consisted of two performances of four songs in front of two separate audiences. The tone was present in two of the four songs at each performance, and in different songs each time. Audience members were asked to detail their emotional state on cards throughout the performance and to make notes of any unusual occurrences they experienced.

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Many of those present reported having unusual experiences during the pieces containing the 17 Hz tone. Audience members reported emotional experiences such as ‘sense of sorrow’, ‘brief moment of anxiety’, ‘excitement’ and physiological experiences such as ‘increased heart-rate’, ‘headache’, ‘tingling in neck and shoulders’, ‘nausea’, and a ‘sense of coldness’.

Subwoofers

To project infrasonic frequencies, a subwoofer must have a frequency range extending sufficiently low to handle the frequencies. Many professional level subwoofers have a low cut- off frequency below 20 Hz, but most consumer home theatre subwoofers cut off somewhere between 20 Hz and 50 Hz. IMAX theatres use custom JBL subwoofers with a low cut-off frequency of 18 Hz, and THX certified theatres must use subwoofers that extend to at least 20 Hz.

In the 1970s several sound enhancement systems were used to project low frequency sound in movie theatres. Universal Studios’ Sensurround was used for the films Earthquake (1974) and Midway (1976), utilising subwoofers with a frequency range of 15 Hz to 100 Hz. Warner Bros’ Megasound, developed in the early eighties and used for the films Altered States (1980) and Superman II (1981), had a low cut-off of 5 Hz, used only to prevent structural damage to the theatre.

Infrasound and Missing Fundamentals

It is possible that infrasonic frequencies could still be projected through subwoofers with a cut off above 20 Hz. Most sound making objects in nature vibrate at numerous frequencies at the same time. When these frequencies are mathematically related to each other as integer multiples they represent the harmonic series. The lowest frequency in the harmonic series is referred to as the fundamental frequency, and the multiples of the fundamental are called harmonics.

When a series of harmonically related frequencies are played together in absence of the fundamental frequency, the fundamental frequency will still be perceived. For example, if tones at 880 Hz, 1320 Hz, 1760 Hz, and 2200 Hz are played simultaneously, the fundamental frequency of 440 Hz would still be perceived by the brain.

A study from the University of North Georgia called An Infrasonic Missing Fundamental Rises at 18.5 Hz indicates that infrasonic frequencies can be perceived by humans using the harmonic series. Subjects were played sine waves corresponding to the first four harmonics of an 18.5 Hz fundamental frequency (37 Hz, 55.5 Hz, 74 Hz, 92.5 Hz) and readings were taken from the auditory cortex using an electroencephalograph. A FFT of the EEG readings showed a distinct peak at 18.5 Hz.

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Infrasound in Film

“Fortunately, in most cases, this effect has yet to be exploited by filmmakers.”

Tomlinson Holman

Low frequency sounds are commonly used in film to increase dramatic tension but infrasonic frequencies have rarely been used in film. It has been reported that two recent films have used infrasound in their soundtracks to elicit a fearful reaction from the audience. During theatrical showings of Gasper Noé’s Irréversible audience members were reported to quickly flee the theatre during the first half hour of the film complaining of feelings of nausea and disorientation. There is noticeable low frequency sound throughout most of the first half of the film, but no evidence of anything below 23 Hz. The director claimed in an interview with Salon.com that they “added 27 Hz of infrasound — a low frequency sound which the police use to stop riots. You can’t hear it, but it makes you shake. In a good theater with a subwoofer, you may be more scared by the sound than by what’s happening on the screen. A lot of people can take the images but not the sound. Those reactions are physical.” While low frequency sound can certainly be used to create dramatic tension in a film, there is no infrasound present in Irréversible.

Left: FFT of opening scene in Irréversible showing a low cut-off frequency between 21 Hz and 23 Hz. Right: FFT of fight scene in Irréversible showing a cut off frequency at 23 Hz.

Left: FFT of “Night One” scene in Paranormal Activity showing a low cut off frequency at about 43 Hz. Right: FFT of ambient sound at the end of Paranormal Activity showing a low cut-off frequency at 29 Hz. During theatrical showings of Paranormal Activity many audience members reported feeling

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petrified throughout the entire film, and it was speculated that their reactions could have been a result of exposure to infrasonic frequencies. At the time of release the official website said that low frequency sounds were used during scenes when the demon was present, but as with Irreversible, there are no infrasonic frequencies present in Paranormal Activity.

Conclusion

The ability of infrasound to cause feelings of fear, feelings of otherworldly presences, visual hallucinations, and other emotional and psychological effects could be beneficially used by horror film sound designers. The addition of infrasonic frequencies to ambient and hard effects could increase unusual feelings in an audience without them being overly aware of the presence of the sound.

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3. Auditory Driving

Brainwave Entrainment

In 1924 German neurologist Hans Berger invented a device called an electroencephalograph (EEG) which records electrical activity from the brain and displays it as waveforms. The EEG lead to Berger’s study of brainwaves, and how different states of consciousness are represented by different electrical frequencies in the brain.

The delta brainwave state designates frequencies from 1 Hz to 4 Hz, and represents the sleep state. Theta waves fall between 4 Hz and 7.9 Hz and represent a relaxed and sleepy state. Frequencies between 8 Hz and 13.9 Hz fall into the alpha category and represent relaxed wakefulness and increased creative thought. Frequencies between 14 Hz and 38 Hz lie in the beta category and represent feelings of focus, alertness, anxiety, and fear.

In 1934 Lord Elger Adrian verified Berger’s work, and discovered that brainwave activity is affected by visual stimulation. In 1949 William G. Walter discovered that visual stimulation affects brainwave activity enough to significantly alter the mental state of subjects.

Synchronising brainwaves to a periodic stimulus in order to induce a specific brainwave state is known as brainwave entrainment. Brainwave entrainment can be induced through the use of EEG biofeedback systems, visual stimulation usually in the form of flashing lights, various aural methods, or a combination called audio-visual entrainment. Brainwave entrainment has frequently and successfully been used to aid in the treatment of sleep disorders, depression, anxiety, addiction, epilepsy, ADHD, and PTST disorder.

Auditory Brainwave Entrainment

Auditory brainwave entrainment, also known as auditory driving, has been proven to affect brainwave frequencies. A paper published in 1999 called Effects of 18.5 Hz audiovisual stimulation on EEG amplitude at the vertex details experiments showing that exposure to an 18.5 Hz auditory entrainment frequency can increase 18.5 Hz EEG activity by up to 27%. In Auditory Driving Observed with Scalp Electrodes in Normal Subjects Andrew Neher details exposure of subjects to drum beats at 3, 4, 6, and 8 beats per second, and finds not only that that the corresponding EEG frequencies are present in all subjects, but that the amplitude and the length of exposure to the drum beats has no effect on the ability of the beat to alter the subjects EEG readings.

Aside from playing a sound at a frequency corresponding to a brainwave state, auditory brainwave entrainment can also be achieved through beats, isochronic tones, and amplitude modulation.

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Beats

Monaural beats occur when two tones close together in frequency and amplitude produce another frequency equal to the difference between the two initial tones caused by the phase relationship of the frequencies (Fig 9). The effect is a result of the ear’s inability to distinguish between the two tones, and it is perceived as one tone with volume surges at a frequency corresponding to the difference between the frequencies.

Combining 440 Hz and 456 Hz sine waves results in a 16 Hz beating frequency.

The existence of binaural beats has been known since their discovery in 1839 by Heinreich Wilhelm Dove, but they weren’t fully understood until Gerald Oster’s 1973 paper Auditory Beats in the Brain. Until Oster’s studies it was thought that the binaural beats effect was an extension of monaural beats and that there were little differences between the two.

While monaural beats can be heard by one or both ears, binaural beats occur when a separate tone is played into each ear, and the beating effect is created within the brain rather than resulting from the phase relationship between the two tones.

While monaural beats are treated by the brain the same as any other entrainment inducing frequency, there is little evidence to suggest that binaural beats cause brainwave entrainment. When monaural beats are heard, the beating frequency reaches the auditory cortex in the same manner as any sound: the sound passes through the ear, into the cochlea where it reaches the auditory nerves, to the thalamus, and to the auditory cortex. Binaural beats are detected in the superior olivary complex, where interaural arrival time and level differences are measured. As with monaural beats, the beating effect is caused by perceived phase differences, but unlike monaural beats, the differences happen in the superior olivary complex instead of in the thalamus. In order for entrainment to occur, the beats must be perceived at the thalamus, not at

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the superior olivary complex.

Most research into the effectiveness of binaural beats on entrainment is performed by The Monroe Institute which is an organisation that sells self-help audio CDs which they claim can induce entrainment. While binaural beats may induce relaxation and improve mood, this cannot be attributed to brainwave entrainment. Impartial studies into the effect of binaural beats on an EEG of the human brain showed that the beats had no significant effect on the subjects.

In Oster’s studies he pointed out some important differences between monaural and binaural beats. While monaural beats can be created with tones of any frequency, binaural beats only occur if the two frequencies are within 26 Hz of each other. Frequencies around 440 Hz work best for binaural beats, and the beating effect vanishes with frequencies above 1000 Hz. The amplitude variation in binaural beats is perceived as a dip of 3 dB, and perceived as total silence with monaural beats. The addition of noise creates a greater effect with binaural beats, and a diminished effect with monaural beats. In order for monaural beats to be effective, the frequencies must be at the same amplitude, but binaural beats will work even if one of the frequencies is below the threshold of hearing.

Isochronic Tones

Isochronic tones are evenly spaced repetitive tones produced in order to achieve brainwave entrainment. They function similarly to monaural beats, but rather than being created by the phase relationship between two frequencies, isochronic tones use evenly spaced tones repeating at a specific frequency.

Clicks being played at frequencies corresponding to the desired brainwave frequency are as successful at achieving auditory entrainment as flashing lights. Applying amplitude modulation to sustained tones can also be used to induce brainwave entrainment. Transparent Corporation claims to have products available which induce brainwave entrainment by applying amplitude modulation to one specific frequency band in a signal, leaving the rest of the frequency spectrum intact, to theoretically embed entrainment producing frequencies into any pre-recorded auditory source. There is little information available on the effectiveness of this technique outside of literature published by Transparent Corporation, but interference with a signal meant to cause entrainment can hamper its effectiveness.

Isochronic tones have been shown to dramatically effect EEG readings. Entrainment through isochronic tones can relieve symptoms associated with myofascial pain syndrome and temporomandibular jaw disorder, including insomnia, dizziness, muscle pain, and headaches.

Entrainment in Music & Film

Repetitive music such as shamanic drumming or electronic trance music in the 4 Hz to 6 Hz

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frequency range can induce the theta brain wave state. Ken Russell’s film Altered States used drumming at this frequency range combined with rapid cuts of the images during a scene when William Hurt’s character was hallucinating from magic mushrooms. The film Raiders of the Lost Ark used monaural beating at about 4 Hz during the scene when the ark was opened.

One second waveform of creature vocalization from The Predator showing transients hitting a rate between 16 Hz and 30 Hz.

One second waveform of Crawler vocalizations from Neil Marshall’s The Descent showing transients hitting a frequency between 16 Hz and 30 Hz The clicking vocalisations of the antagonist in the 1987 film Predator and the Crawlers in Neil Marshall’s The Descent both repeat at a frequency between 16 and 30 Hz, falling in the Beta range. It is hard to say whether this was done deliberately, but it is impossible to deny the ability of the creatures’ vocalisations to cause shivers in the spines of the audience.

Conclusions

With plenty of evidence to show that auditory driving can be used to achieve delta, theta and alpha brainwave states, there is no reason to expect that beta states can’t also be induced through auditory driving. It is likely that using monaural beats, isochronic tones, amplitude modulation and even sequencing or performing sounds in the range of 24 Hz and higher can induce a beta brainwave state in a listener.

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4. Nonlinear Sound

Nonlinear sound can be defined as sound that has become distorted or non-harmonic when the sound reaches a level that the system producing or propagating the sound can not reproduce or maintain. Characteristics of nonlinear sound are noise, abrupt frequency and amplitude changes, and inharmonic sidebands.

Humans and other animals produce a number of nonlinear vocalisations, including screams and cries of distress with rapid changes in frequency and amplitude. It is believed that the discordant qualities of these sounds, and the rapid changes in frequency and amplitude exist to attract the attention of those perceiving the sounds.

Nonlinear sound has been shown to cause feelings of fear, increased awareness, and negative valence.

Vestigial Reflex Response

In the 1980s a study was conducted to determine what is considered to be the most unpleasant sound, and the results were detailed in Psychoacoustics of a Chilling Sound by D. L. Halpern, R. Blake, and J. Hillenbrand. The researchers selected eight sounds that they expected to be perceived as unpleasant, and eight sounds they expected to be perceived as neutral or pleasant, and subjects were asked to rate them on a 15 cm scale of unpleasant to pleasant.

The nine worst rated sounds contained nonlinear characteristics. The results showed a ‘scraping slate’ sound resembling the sound of fingernails scraping on a chalkboard to be rated the worst.

In the second part of the study the researchers wanted to determine how much the frequency content of the ‘scraping slate’ sound could be altered while still maintaining its unpleasantness. They ran the sound through several filters to remove frequency content in different bands, and again asked listeners to judge how unpleasant they were. A low-pass filter with a cut-off frequency between 8 and 3 kHz had no effect on the perceived unpleasantness of the sound. A high-pass filter with a cut-off frequency of 2 kHz was perceived to be just as unpleasant as the original sound, and raising the cut off frequency diminished the unpleasantness of the sound. These results show that the middle frequency band contains the frequencies causing the unpleasantness.

While no solid reasons were offered regarding why these sounds are perceived as unpleasant, in their report the researchers noted that a spectrogram of the ‘scraping slate’ resembled that of a warning cry of a macaque monkey, and they hypothesised that the sound may be similar to vocalisations of predatory animals. It was suggested that humans’ reactions to sounds of this type could be the result of a vestigial reflex response to these animal vocalisations still present in the human brain.

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Dissonance

An internet based experiment by Trevor J Cox examined reactions to thirty-four horrible sounds. A website was created where participants were asked to rate the “horribleness” of the sounds on a scale of one to seven, one being “not horrible”, and seven being “horrible.”

Cox wanted to explore Blake’s vestigial reflex theory further, and while some of the reactions to the sounds could be a result of the vestigial reflex response, Cox found the results for the ‘fingernails scraping down a blackboard’ sound weren’t consistent with this theory. He claimed that the unpleasantness of the sounds may be based on the dissonant qualities of the sounds, and suggested that our aversion to dissonance could be a result of our auditory system being trained to seek out the harmonic content inherent in speech, or the ability of dissonant sound to interfere with our ability to clearly distinguish any sounds in the presence of inharmonic interference.

Loudness, Surround, and Increased Pitch

In A Preliminary Experiment to Assess the Fear Value of Sound Parameters in a Survival Horror Game the authors detail a study done to determine the effects of surround sound, increased loudness, and increased pitch on the fear level of players of a videogame. The sounds used in the game were a zombie call, a twig snap, a woman screaming, a monster attack, and an intense scream. The same sounds were used in four levels of one game. The first level used the sounds in their original state, the second level had the pitch of the effects raised by 300 cents, the third level used 3D sound to place the effects beside the player, and the fourth level raised the effects by 25 dB. Players were asked to verbally rate their emotional response to the sounds during game play. The researchers found that there was no evidence to indicate that these three parameters affected the intensity of the players’ response. The researchers believed that if they had used less conservative treatments of the sound effects, they would have gotten a more intense response from the participants.

Nonlinear Sound in Film & Music

Based on the ability of nonlinear sound to attract attention, Daniel T. Blumstein hypothesised that nonlinear sound may be used in film sound to affect the emotional state of listeners. Blumstein and his associates took a selection of sound clips from films in different genres, and searched for sounds that would be perceived as nonlinear if they had been produced in nature which they called nonlinear analogues. They found that diegetic noisy nonlinear analogues and noisy sidebands are frequently used in horror films to elicit a fearful response.

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Spectrograms of violins from the shower scene in Alfred Hitchcock’s Psycho (left) and flashbulb sound effect from Tobe Hooper’s Texas Chainsaw Massacre (right), both showing harmonic dissonance and frequency upshifts. Music with nonlinear characteristics has a greater emotional effect on listeners than music without nonlinear characteristics. In another study Blumstein had 42 subjects listen to and rate 36 compositions containing nonlinear analogues. The researchers composed twelve ten-second compositions, then altered the compositions by adding noise through the use of instrumentation changes or electronic distortion, or frequency downshifts and upshifts. The listeners were asked to rate their emotional reactions to the compositions based on their arousal and negative valence on a scale of -5 to +5.

Music that contained noise or upward frequency shifts was found to increase arousal in the subjects, while downward frequency shifts had no effect on arousal. Subjects reported an increase in negative valence in the compositions containing noise and downward frequency shifts, but not with upwards frequency shifts.

An aroused and aversive reaction to noise may be associated with nonlinear sound present in human and animal vocalisations while in distress. The increased arousal present with frequency upshifts, and not present with frequency downshifts, may be associated with the tightening of vocal chords.

Conclusions

Whether because of a vestigial reflex response or reactions to dissonant sound, nonlinear sound can cause unpleasant feelings, heightened awareness, negative valence, and fear. Nonlinear sound is frequently used in music and dialog in horror films, and it is presumed that applying the same characteristics to sound effects would garner a similar reaction. While the use of distortion, inharmonic sidebands, and abrupt frequency upshifts and downshifts can be used to attain an increased negative emotional response from an audience, increased loudness, increased pitch, and surround sound techniques do not have a similar effect.

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5. Infrasound in Sound Effects

In order to be effective, infrasonic frequencies should be hidden in low frequency sounds, but still be at a higher amplitude than the rest of the sound. Our ears have a very steep roll off below 20 Hz, so care has to be taken to balance the sounds properly.

One technique that works well is to apply a low-pass filter between 200 and 500 Hz to a recording that already has a lot of bass information. For sounds with a steep roll off well above 20 Hz Waves LoAir or MaxBass plug-ins can help even out the bass frequencies, or add low frequencies where there are none.

Low-pass filter, Noise Gate and Waves LoAir plug-ins used in design of infrasonic sound effects.

Playing a high amplitude low frequency along with a recorded sound will naturally sound like exactly what it is: a low frequency tone being played under a recording. In order to hide the infrasonic frequencies in the sounds the right type of waveform must be used, and it should follow the natural amplitude envelope of the sound that is disguising it. Anything other than pure sine waves are usually too noticeable, but may be appropriate in some cases, depending on the accompanying sounds in the effect.

Applying a noise gate to the infrasonic tone and side-chaining it to the recording it’s being used with will allow the amplitude of the tone to follow the envelope of the recorded sound. Care should be taken to set the attack and release of the noise gate properly so that the amplitudes change in sync. Alternatively, the volume of the infrasonic frequency can be automated to match the recorded sound.

Effects with infrasonic missing fundamentals can be generated using the above techniques, but rather than using an infrasonic tone, only the harmonics of the tone are used in the creation of the effect, with the amplitude of each harmonic tone decreasing as the frequency increases.

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FFTs of an 18.5 Hz sine wave, harmonics of an 18.5 Hz sine wave, and the fundamental and harmonics of the tone.

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6. Auditory Driving in Sound Effects

Amplitude modulation with low frequency oscillators, monaural beats, delay units, and manually editing transients onto a grid can be used to produce brainwave entrainment inducing frequencies.

Amplitude Modulation

Any sampler or soft sampler will include a low frequency oscillator which has the ability to sync to an external rate through MIDI or within a session file. The parameters in Logic’s EXS24 sampler can be synced to a session’s BPM rate, and also allows rates of 0.125 Hz to 32 Hz to be selected, although with higher frequencies it is impossible to input precise values. If exact frequencies aren’t required, the EXS24 LFO is perfectly capable of generating isochronic tones within a pre-recorded sample in a Logic sample instrument. The Waves MondoMod plug-in is superior in that it is a stand alone LFO that can be applied to an audio file, it allows any frequency up to 60Hz to be used or it can be synced to the project’s bpm rate, and it has controls for amplitude modulation depth and frequency modulation depth, allowing the isochronic tones to be mixed with the original file as desired.

Monaural Beats

Monaural beats are simple to create, and can be very effective for auditory driving. Using Audacity, or any software that allows tones at specific frequencies to be generated, tones separated in frequency by the desired beating frequency and bounced out at a common amplitude will create monaural beats.

While pure sine waves and frequencies between 100 Hz and 10 kHz will have the same effect, they don’t provide very interesting sounds, and come across more as chords than beats. Sawtooth and square waves lower than 100 Hz and above 10 kHz result in more sonically interesting sounds.

Delay Units

Delay plug-ins can be used to apply repetitive delays to a signal in the beta frequency range. Depending on the delay rates available in the delay unit, syncing the delay unit to a session’s bpm rate and modifying the bpm rate and the delay rate will result in a delay of a chosen frequency. For example, if a session is set to 240 bpm, and a sixteenth-note delay rate is chosen, a delay of 16 Hz will be generated.

Grids

A very tedious but effective way of generating isochronic tones is to manually cut audio files with many quick transients, and set them to a grid in a DAW. If the bpm rate of a session is set to 60 bpm in 4/4 time, and the bars are divided in fourths, you are left with a 1 Hz grid. If the bar division is set to 64 at this bpm rate, a 16 Hz grid is visible.

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Creating isochronic tone effects in Logic by cutting and locking to a grid.

Any recordings with quick transients and a short tail can be used in this technique, for example, quick drum hits, or clicking sounds. The simple method is to select one hit in a recording and copy and paste it, or loop it in the grid. The tedious but more interesting and effective method is to cut up all of the hits in a recording and set them to the grid.

From here the bpm rate of the session can be modified to generate isochronic tones at varying frequencies, while ensuring that everything stays on the grid. If a 16 Hz isochronic tone is created at 60 bpm, changing the tempo to 75 bpm will generate a 20 Hz isochronic tone, at 90 bpm 24 Hz will be generated, at 105 bpm 28 Hz will be generated, and at 120 bpm 32 Hz will be generated. Alternatively, if a 32 Hz isochronic tone is created at 60 bpm, it’s a matter of working backwards by 7.5 bpm until a 16 Hz tone is generated at 30 bpm.

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7. Nonlinear Sound in Sound Effects

The key properties of nonlinear sound are distortion and noise, inharmonic sidebands, and frequency upshifts and downshifts.

Distortion

The obvious way to emulate noise and distortion is by simply distorting a signal. Adding distortion to a sound effect will simply sound like a distorted sound effect, so in cases when it is desired to add nonlinear qualities to a sound but not have them sound like they’ve simply been distorted, distortion can be hidden somewhere in the frequency spectrum of the sound, while leaving the rest of the sound untouched. In order to do so, the recording can be duplicated, either by bussing the signal to another track, or by duplicating the recording, so that two versions of the same sound can be processed separately. By using a band pass filter on the duplicated or bussed track centered on the frequencies which will be distorted, followed by a distortion unit, only those frequencies will be affected, and the remaining frequencies will still be heard clearly from the original sound.

D16 Devastor and Decimort plug-ins used to apply distortion to specific frequency bands in construction of sound effects emulating nonlinear sound.

Different distortion plug-ins are better at treating different frequency bands. Logic’s Bitcrusher plug-in works really well on high frequencies, providing a piercing bit-crushing effect which can easily be hidden among lower frequencies, but is not as efficient at dealing with hi-mids and anything below. The Soundtoys Decapitator plug-in works really well with lows and mids, providing an accurate emulation of analogue tape saturation which comes through as a highly compressed and warmly distorted signal. The Decimort plug-in from D16 is a very versatile bit crushing effect which works really well on the entire frequency spectrum which allows the

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sample rate to be compressed as well as the bit depth. It also comes with a filter section which can be switched between pre and post bit crushing to easily affect only a specific frequency band. The D16 Devastor is a multiband distortion unit with three filters, which can also be used pre or post distortion, and also works well for distortion effects being applied to a specific frequency band.

Another technique for hiding distortion in a sound effect is to record sounds with fast transients too hot, so they truncate while being recorded., then incorporating the recording into the design of the effect. It is important that the sounds are normalised to at least -0.3 dBFS, or the gain is lowered to an appropriate level before being used in designing a sound effect, otherwise the entire effect will peak.

Inharmonic Sidebands

There are a number of ways to generate inharmonic sidebands. Any DAW will include a pitch shifting plug-in, which can be used to alter the pitch of a signal. By duplicating or bussing a recording multiple times and altering the pitch of the duplicates any chord can be generated with the recorded sounds. In order for the side bands to be inharmonic, minor seconds or diminished fifths should be used, and can easily be created by raising or lowering the signal by semitones, or at 100 cents for one semitone if semitones can’t be changed in the plug-in parameters.

Duplicating audio files and changing the frequency of the duplicates with Waves Soundshifter plug-in.

Logic’s pitch shifting plug-in causes latency in the signal, so isn’t great for this effect if there are prominent transients in the signal. The Waves SoundShifter plug-in does a much better job while not causing latency or obvious artefacts.

Another technique for generating inharmonic sidebands is to duplicate and edit the audio file, rather than using a plug-in, then layering the modified files. Logic’s sample editor generates ugly

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artefacts in the signal, but good results can be gotten with Pro Tools AudioSuite without obvious artefacts by raising or lowering the duplicated file by the desired number of semitones or cents.

Frequency Shifts

There are several ways to create frequency downshifts and upshifts in a recording. If samples or MIDI instruments are being used, any DAW will allow automation of pitch bends. If audio files are being used, which is more likely, Melodyne is a very user friendly way to create pitch bends, as well as inharmonic sidebands in a recording.

The Waves Doppler plug-in is probably best suited for emulating the frequency shifts in nonlinear sound. In it’s default mode, it simulates the Doppler effect by raising the frequency and amplitude up to a chosen centre time, then decreasing frequency and amplitude while moving from the left or right stereo channel to the opposite channel. The parameters can be modified to create quick frequency upshifts and downshifts while not changing the amplitude or moving through the stereo spectrum, if desired.

The best ways to emulate nonlinear sound is to record things which already contain characteristics of nonlinear sound, or are the result of nonlinearities in a system, and incorporate them into sound effect design. Feedback and screaming or yelling are a result of the system producing the sound being pushed to its limit causing distortion, frequency shifts, and inharmonic sidebands. The same effect can be achieved by abusing musical instruments, for example, blowing too hard into a brass or woodwind instrument, or roughly bowing a cymbal or string instrument.

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8. Analysis

Using these techniques, a sound effects library called Psychoacoustic Horror was created. Analysis was done on the effects, and a series of listening tests were held in order to determine the overall effectiveness of these techniques.

Infrasound

During Vic Tandy’s research into infrasound and paranormal phenomena he found sites that were believed to be haunted had infrasonic frequencies present at a greater amplitude than other ambient sounds. Fast Fourier Transforms of the infrasonic sound effects in Psychoacoustic Horror show the infrasonic frequencies and their harmonics at a greater amplitude than the other elements in the sound effects.

FFTs of infrasonic effects in Psychoacoustic Horror. Previous studies into the effects of infrasonic frequencies determined that frequencies between 17 Hz and 19 Hz could cause a decrease in mood, cold chills, and feelings of an unknown presence, and that the harmonic series can be used to register an infrasonic missing fundamental in the auditory cortex.

The listening test results indicate that exposure to an infrasonic missing fundamental at 18.5 Hz caused 93% of participants to quickly experience decreases in mood of varying degrees. Later exposure to an infrasonic missing fundamental caused 66% of participants to experience a decrease in temperature. At a third instance of an infrasonic missing fundamental, subjects, who were sitting alone in a room, were asked whether they felt alone while taking the test. While 40% of participants reported that they felt alone, 60% reported that they did not feel completely alone.

Auditory Driving

Studies have shown that auditory driving can be used to synchronise a subject’s brainwaves to an external stimulus, that the length of exposure to the stimulus has no effect on it’s ability to cause entrainment, and that monaural beats and isochronic tones can be used to induce auditory brainwave entrainment. For beta brainwave entrainment to occur, a subject must be exposed to evenly spaced tones at a rate of approximately 16 Hz to 32 Hz. Stimulation of beta brainwaves

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can cause listeners to feel active, alert, anxious, and fearful.

One second waveforms of isochronic tone effects in Psychoacoustic Horror showing frequencies of 16 Hz 20 Hz 24 Hz 28 Hz and 32 Hz.

The effects in Psychoacoustic Horror which incorporate auditory driving frequencies were all created using monaural beats, amplitude modulation, isochronic tones, and delay units. When the waveforms of the effects are viewed, evenly spaced tones at the desired frequencies can be seen (Fig 78).

During the listening tests, exposure to isochronic tones between 16 Hz and 32 Hz caused 100% of subjects to quickly experience feelings of alertness, and 87% to feel more energetic. Exposure to a 32 Hz monaural beating frequency caused 100% of subjects to experience a greater level of discomfort than they previously reported.

Exposure to a 16 Hz monaural beating frequency caused 60% of subjects to report feeling more anxious than relaxed. The introduction of a 32 Hz beating frequency caused 73% of subjects to report feeling more anxious than relaxed. 66% of subjects reported an increase in anxiety upon exposure to the 32 Hz beating frequency.

Nonlinear Sound

Studies have shown that exposure to sounds containing characteristics of nonlinear sound such as distortion, rapid frequency shifts, and inharmonic sidebands can cause listeners to experience feelings of anxiety, increased awareness, aversiveness, and fear. Distortion, frequency shifts, and discordant sidebands were used in the construction of a series of sound effects in Psychoacoustic Horror.

Spectrograms of sound effects that contain inharmonic sidebands clearly show dissonant frequency information. Sounds which were constructed to contain frequency shifts show clear frequency shifts in the spectrograms. Sounds with naturally occurring nonlinear sound can be seen to have harmonic distortion, frequency shifts, and inharmonic sidebands.

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Spectrograms of sound effects in Psychoacoustic Horror containing distortion, harmonic dissonance, and frequency shifts. During listening tests, 87% of subjects reported an increase in their level of fear after initial exposure to sound effects containing distortion, frequency shifts and dissonant sidebands, and 100% of subjects reported feeling an aversion to these sounds. Later exposure to effects containing these three properties caused 80% of participants to report feeling more angry than content. A third instance of exposure to sound effects with all three properties caused 60% of participants to report feeling more nervous than calm, and prolonged exposure caused 54% of participants to report an increasing level of anxiety.

Exposure to sound effects containing inharmonic sidebands and frequency shifts without distortion caused 53 % of participants to report feeling more frightened than calm.

During exposure to a series of effects with added distortion only in certain frequency bands caused 100% of subjects reported an increased level of alertness. A later instance of sound effects with added distortion caused 60% of participants to report an increased level of fear, with the fear level increasing in 67% after prolonged exposure.

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9. Conclusions

Throughout the listening tests the emotional reaction of the participants mostly followed the expected pattern. Before the tests it was unknown which effects would have the greatest effect on listeners. Exposure to effects containing infrasonic missing fundamentals and auditory driving frequencies caused the majority of participants to consistently experience the expected emotions through the test.

Before the listening tests, the effects of an infrasonic missing fundamental on listeners was unknown. The results of the listening tests indicate that exposure to an infrasonic missing fundamental can have similar effects on the majority of listeners to real infrasound.

The listeners’ reactions to nonlinear sound seem to be dependant on which elements of nonlinear sound have been incorporated in the design of the effect, and what sounds they had previously been exposed to. Effects containing distortion caused an increase in reported feelings of fear and anxiety in the majority of participants, but sounds which only incorporated inharmonic sidebands or frequency shifts did not have as strong an effect, although the majority of subjects still reported experiencing anxiety.

It is possible that the emotional response garnered from some of these techniques can outweigh the emotional response from others. Exposure to dissonant sounds with frequency shifts alone may cause a listener to experience a high level of anxiety, but after exposure to infrasonic frequencies or beta frequency isochronic tones, exposure to dissonance and frequency shifts may cause listeners to experience relief.

Upon completion of analysis and objective listening tests of sound effects created using infrasound, auditory driving, and nonlinear sound, it can be seen that these techniques can be used to get a strong emotional and psychological response from listeners, and thus help to create a move enjoyable and involving experience for an audience.

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10. Recommended Reading

Blumstein, D. T., Davitian, R., Kaye, P. D., 2010. Do film soundtracks contain nonlinear analogues to influence emotion?[pdf] Biology Letters. Available at: http://rsbl.royalsocietypublishing.org/content/6/6/751.full.pdf+html

Blumstein, D. T., Bryant, G. A., Kaye, P. D., 2012. The sound of arousal in music is context dependant. [pdf] Biology Letters. Available at: http://www.gregbryant.org/sound_of_arousal_BL2012.pdf

Braine, J., 2006. A Study of the Effects of Acoustic Phenomena and Their Possible Use in Multimedia 2006 [pdf] Available at: http://www.johnbraine.com/words/AcousticPhenomena.pdf

Chen, H. A., Narins, P. Wind Turbines and Ghost Stories: The Effects of Infrasound on the Human Auditory System [pdf] Los Angeles. Available at: http://www.library.ucla.edu/pdf/Chen.Paper.pdf

Cox, T. J., 2007. Bad Vibes: An Investigation into the Worst Sounds in the World [pdf] International Conress on Acoustics Madrid. Available at: https://getinfo.de/app/Bad-vibes-an-investigation-into-the-worst-sounds/id/BLCP %3ACN068632716

Cox, T. J., 2008. Scraping Sounds and Disgusting Noises [pdf] Available at: http://usir.salford.ac.uk/12958/2/ final_disgusting_scraping_applied_acoustics_usir.pdf

Frederick, J., Lubar, J., Rasey, H., Brim, S., & Blackburn, J., 1999. Effects of 18.5 Hz audiovisual stimulation on EEG amplitude at the vertex. Journal of Neurotherapy, 3 (3), 23-27.

Garner, T., Grimshaw, M., Nabi, D. A., 2010. A Preliminary Experiment to Assess the Fear Value of Sound Parameters in a Survival Horror Game [pdf] Available at: http://ubir.bolton.ac.uk/index.php? action=fileDownload&resourceId=238&hash=cd223eb4b2143b6bf5af3541952d4e6625453482& filename=gcct_conferencepr-14.pdf

Halpern, D. L., Blake, R., Hillenbrand, J., 1986. Psychoacoustics of a Chilling Sound [pdf] Perception & Psychophysics. Available at: http://link.springer.com/article/10.3758%2FBF03211488

Lacomba, C. D., Lloyd, S. A., Shanks, R. A., 2013. An Infrasonic Missing Fundamental Rises at 18.5 Hz [pdf]

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Available at: http://digitalcommons.northgeorgia.edu/papersandpubs/vol2/iss1/11/

Leventhall, G., 2003. A Review of Published Research on Low Frequency Noise and its Effects [pdf] Available at: http://westminsterresearch.wmin.ac.uk/4141/1/Benton_2003.pdf

Magalhaes, M. D. C., Robinson, M., Cox, T. J., 2009. The Effects of Frequency Response on the Perception of Unpleasant Sounds Using The Method of Pair Comparison [pdf] The Sixteenth International Congress on Sound and Vibration. Available at: http://www.iiav.org/archives_icsv/2009_icsv16/content/technical_papers/60.pdf

Neher, A., 1960. Auditory Driving Observed with Scalp Electrodes in Normal Subjects [pdf] Available at: http://www.stanford.edu/group/brainwaves/2006/AndrewNeherAuditoryDriving.pdf

Oster, G., 1973. Auditory Beats in the Brain [pdf] Available at: http://cherigustafson107.vpweb.com/G%20Oster%20-%20Auditory%20Beats %20in%20the%20Brain.pdf

Siever, D. Article One – Audio-Visual Entrainment: History and Physiological Mechanisms [pdf] Available at: http://www.mindalive.com/1_0/article%201.pdf

Siever, D., 2009. Entraining Tones and Binaural Beats [pdf] Mind Alive. Available at: http://www.mindalive.com/1_0/article%2012.pdf

Sonnenschein, D., 2001. Sound Design: The Expressive Power of Music, Voice, and Sound Effects in Cinema. Studio City: Michael Wiese Productions

Tandy, V., Lawrence, T. R., 1998. The Ghost in the Machine. [pdf] The Journal of the Society for Psychical Research. Available at: http://www.hauntmastersclub.com/files/ghost-in-machine.pdf

Tandy, V. Something in the Cellar [pdf] The Journal of the Society for Psychical Research. Available at: http://www.richardwiseman.com/resources/Something-in-the-Cellar.pdf

Tempest, W., 1976. Infrasound and Low Frequency Vibration. London: Academic Press

Vernon, D., Peryer, G., Louch, J., Shaw, M., 2012. Tracking EEG changes in response to alpha and beta binaural beats. [pdf] International Journal of Psychophysiology. Available at: http://www.sciencedirect.com/science/article/pii/S0167876012006241#

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