Theory of Sound and Hearing--Three Elements of Sound

Because the human ear auditory system is very complex, so far, humans have not been able to fully explain its physiological structure and auditory characteristics from the perspective of physiology and anatomy. Therefore, the research on human hearing characteristics is currently in psychoacoustics and speech acoustics.

The human ear's hearing range for sounds of different intensities and frequencies is called the sound range. Within the range of the human ear, the subjective feelings of sound auditory psychology mainly have characteristics such as loudness, pitch, timbre, masking effect, and high-frequency localization. Among them, loudness, pitch, and timbre can be used subjectively to describe any complex sound with three physical quantities of amplitude, frequency and phase, so it is also called the "three elements" of sound; and in a variety of sound sources, the ear masking effect And other characteristics are more important, it is the basis of psychoacoustics. Here is a brief introduction to the above issues.

1. The three elements of sound

1. Loudness

Loudness, also known as sound intensity or volume, it represents the strength of sound energy, which mainly depends on the amplitude of sound waves. The loudness of sound is generally measured by sound pressure (dyne/square centimeter) or sound intensity (watts/square centimeter). The unit of sound pressure is Pa (Pa), and the logarithmic value of its ratio to the reference sound pressure is called the sound pressure level. , The unit is decibel (dB). The psychological perception of loudness is generally measured by the unit Sone, and the loudness of a pure tone of 1 kHz and 40 dB is defined as 1 Song. The relative amount of loudness is called loudness level, which represents the logarithmic value of the ratio of a certain loudness to the reference loudness, and the unit is phon, that is, when the human ear feels that a certain sound is as loud as a pure sound of a single frequency of 1kHz, the sound The decibel of the sound pressure level is its loudness level. It can be seen that both objectively and subjectively, the concepts of these two units are completely different. Except for 1kHz pure tone, the value of sound pressure level is generally not equal to the value of loudness level, so pay attention to it during use.

Loudness is the basis of hearing. The intensity range of normal human hearing is 0dB-140dB (some people think it is -5dB-130dB). Of course, the sound beyond the audible frequency range of the human ear (that is, the frequency domain), even if the loudness is louder, the human ear cannot hear it (that is, the loudness is zero). But in the audible frequency domain of the human ear, if the sound is weak or strong to a certain level, the human ear can't hear it either. When the sound is reduced to the point that human ears can just hear it, the sound intensity at this time is called the "hearing threshold". Generally, the measurement is based on 1kHz pure tone. The sound pressure that the human ear can hear is 0dB (usually greater than 0.3dB), and the loudness level when the sound intensity is 10-16W/cm2 is set as 0 square. When the sound is increased to make the human ear feel pain, this threshold is called the "pain threshold". The measurement is still based on 1kHz pure tone, so that the sound pressure level when the human ear feels pain is about 140dB.

Experiments show that the threshold of hearing and pain vary with sound pressure and frequency. The area between the equal loudness curve (Fletcher-Munson curve) of the hearing threshold and the pain threshold varying with frequency is the hearing range of the human ear. It is generally believed that for 1kHz pure tone, 0dB-20dB is a quiet sound, 30dB-40dB is a weak sound, 50dB-70dB is a normal sound, 80dB-100dB is a loud sound, and 110dB-130dB is an extremely loud sound. For audible sounds other than 1kHz, there are countless equivalent sound pressure-frequency values on the same level of loudness curve. For example, a 30dB sound at 200Hz and a 10dB sound at 1kHz sound the same loudness in the human ear. , This is the so-called "waiting sound". It is inaudible when the hearing threshold is less than 0dB and the pain threshold is greater than 140dB. Even the sound in the sensitive frequency range of the human ear can not be noticed by the human ear. The human ear has different thresholds and sensitivity to sounds of different frequencies. The pain threshold of the human ear is not greatly affected by frequency, while the hearing threshold changes quite drastically with frequency. The human ear is sensitive to sounds from 3kHz to 5kHz, and sound signals with very small amplitudes can be heard by the human ear. In the low frequency area (such as less than 800Hz) and high frequency area (such as greater than 5kHz), the human ear has a low sensitivity to sound. many. When the loudness level is small, the sensitivity of high- and low-frequency sounds is significantly reduced, and the sensitivity of the low-frequency range is more severe than that of the high-frequency range. Generally, special attention should be paid to enhancing the low-frequency volume. Generally speaking, the sound pressure level of 200Hz--3kHz is 60dB-70dB, and the sound pressure of music with a wide frequency range is 80dB-90dB.

2. pitch

Pitch is also called pitch, which represents the subjective perception of the human ear to the pitch of a sound. Objectively, the size of the pitch mainly depends on the fundamental frequency of the sound wave. The high frequency means the high pitch, and vice versa. The unit is expressed in hertz (Hz). The subjectively felt pitch unit is "beauty", and the pitch of a 1kHz pure tone with a loudness of 40 squares is usually defined as 1000 US. Hertz and "beauty" are also two different concepts of pitch but related units.

The human ear's perception of loudness has a range from the threshold of smell to the threshold of pain. The human ear's perception of frequency also has a range from low audible frequency 20Hz to high audible frequency 20kHz. The measurement of loudness is based on a pure tone of 1kHz. Similarly, the measurement of pitch is based on a pure tone with a sound intensity of 40dB. Experiments have proved that the change between pitch and frequency is not linear. In addition to frequency, pitch is also related to the loudness and waveform of the sound. The change in pitch is proportional to the logarithm of the relative change of the two frequencies. Regardless of the original frequency, as long as the two 40dB pure tone frequencies are increased by 1 octave (that is, 1 times), the pitch change felt by the human ear is the same. In music acoustics, the continuous change of pitch is called portamento, and one octave is equivalent to an octave increase in musical tone. According to the human ear’s actual perception of the pitch, the human voice frequency range can be widened to 80Hz--12kHz, the musical sound is wider, and the effect sound is wider.

3. Timbre

Tone color is also called timbre, which is determined by the harmonic spectrum and envelope of the sound waveform. The clearly audible sound produced by the fundamental frequency of the sound waveform is called the fundamental tone, and the sound produced by the small vibration of each harmonic is called the overtone. The tone of a single frequency is called pure tone, and the tone with harmonics is called polyphony. Each fundamental tone has a natural frequency and overtones of different loudness, which can distinguish other sounds with the same loudness and pitch. The proportion of each harmonic of the sound waveform and the attenuation over time determine the timbre characteristics of various sound sources. The envelope is the connection between the peaks of each cycle. The steepness of the envelope affects the transient characteristics of the sound intensity. The timbre of sound is varied and varied. The goal of Hi-Fi audio is to transmit and restore all the characteristics of the original sound field as accurately as possible, so that people can actually feel the sense of sound source localization and spatial envelopment. Three-dimensional surround sound effects with various on-the-spot listening senses such as sense of depth, layering and thickness.

In addition, other physical characteristics that characterize sound include: sound value, also known as sound length, which is determined by the duration of vibration. If the duration is long, the sound will be long; otherwise, it will be short. From the above three main characteristics of subjective description of sound, the auditory characteristics of the human ear are not completely linear. After the sound is transmitted to the human ear and processed, in addition to the fundamental tone, various homophonic sounds and their harmony and difference will be produced. Not all of these components can be felt. The human ear has the functions of receiving, selecting, analyzing, and judging loudness, pitch and timbre. For example, the human ear can only perceive the envelope of the time-domain waveform that has a decisive influence on sound localization (especially The fast-changing envelope is the delay of the inner ear), and the waveform of a single cycle cannot be sensed and the direction of high-frequency signals with very close frequencies cannot be judged; and the resolution of the sound amplitude is low, and the phase distortion is not sensitive. These involve complex problems in psychoacoustics and physiological acoustics.