1. Subjective perception in the frequency domain
The important subjective feeling in the frequency domain is pitch. Like loudness, pitch is also a subjective psychological quantity of hearing, which is the attribute of hearing to judge the level of sound. The difference between pitch in psychology and scale in music is that the former is the pitch of pure tones, while the latter is the pitch of composite sounds such as music. The pitch of a composite sound is not only a frequency analysis, but also a function of the auditory nervous system, which is affected by the listener’s listening experience and learning.
2. Subjective feelings in the time domain
If the duration of the sound exceeds about 300ms, the increase or decrease of the duration of the sound has no effect on the change in the threshold of hearing. The perception of tone is also related to the duration of the sound. When the sound lasts for a short time, no tone can be heard, just a “click” sound. Only when the sound lasts for more than tens of milliseconds can the perceived pitch be stable. Another subjective sensory characteristic of the time domain is echo.
3. Subjective perception of the spatial domain
Binaural listening for human ears has obvious advantages over monaural listening. It has high sensitivity, low listening valve, a sense of direction to the sound source, and stronger anti-interference ability. Under stereo conditions, the sense of space obtained by listening with speakers and stereo headphones is different. The sound heard by the former seems to be in the surrounding environment, while the sound heard by the latter is inside the head. In order to distinguish between the two The sense of space, the former is called orientation, and the latter is called positioning.
4. Weber’s law of hearing
Weber’s law states that the subjective perception of human hearing sounds is proportional to the logarithm of the objective stimulus. When the sound is small and the sound wave amplitude is increased, the subjectively perceived volume of the human ear increases by a larger amount; when the sound intensity is higher and the same sound wave amplitude is increased, the increase in the subjectively perceived volume of the human ear is smaller.
According to the above-mentioned listening characteristics of the human ear, it is required to use an exponential potentiometer as a volume controller when designing a volume control circuit, so that the volume increases linearly when the potentiometer handle is evenly rotated.
5. Ohm’s law of hearing
Scientist Ohm discovered Ohm’s law in electricity, and he also discovered Ohm’s law in human hearing. This law reveals that the human ear’s hearing is only related to the frequency and intensity of each partial sound in the sound, but is related to each partial sound. The phase between is irrelevant. According to this law, the process of recording and playback in the audio system can be controlled without considering the phase relationship of the partial tones in the complex sound.
The human ear is a frequency analyzer, which can separate the homophony in the polyphony. The human ear has a high sensitivity to frequency resolution. At this point, the human ear has a higher resolution than the eye, and the human eye cannot see all kinds of white light. Color light components.
6. Masking effect
Other sounds in the environment will reduce the listener’s hearing of a certain sound, which is called masking. When the intensity of one sound is much greater than that of the other sound, and when the two sounds exist at the same time, people can only hear the sound of the loud one, but cannot detect the existence of the other sound. The amount of masking is related to the sound pressure of the masking sound. As the sound pressure level of the masking sound increases, the amount of masking increases. In addition, the masking range of low-frequency sounds is larger than that of high-frequency sounds.
This auditory characteristic of the human ear provides important inspiration for designing noise reduction circuits. In tape playback, there is such a listening experience. When the music program is continuously changing and the sound is loud, we will not hear the background noise of the tape, but when the music program ends (blank tape), we can feel The “his…” noise to the tape exists.
In order to reduce the influence of noise on the program sound, the concept of signal-to-noise ratio (SN) is proposed, that is, the signal strength is required to be sufficiently larger than the noise strength, so that the listening will not feel the presence of noise. Some noise reduction systems are designed using the principle of masking effect.
7. Binaural effect
The basic principle of the binaural effect is this: if the sound comes from directly in front of the listener, at this time, since the distance from the sound source to the left and right ears is equal, the time difference (phase difference) and tone color difference for the sound wave to reach the left and right ears is Zero, at this time, the sound is felt from the front of the listener, not to one side. When the sound is different, you can feel the distance between the sound source and the listener.
Haas’s test proved that when two sound sources sound at the same time, the experience of binaural listening is different according to the delay between one sound source and the other sound source, which can be divided into the following three situations to illustrate :
(1) When the delay between one sound source and the other of the two sound sources is within 5～35mS, it is as if the two sound sources are combined into one, and the listener can only feel that the sound source is ahead of the other sound source. Existence and direction, without feeling the existence of another sound source.
(2) If one sound source delays the other by 30-50mS, the presence of two sound sources can already be felt, but the direction is still determined by the leader.
(3) If the delay of one sound source is 50mS greater than that of the other sound source, two sound sources can be felt at the same time, the direction is determined by each sound source, and the delayed sound is a clear echo.
The Haas effect is one of the foundations of stereo system orientation.
9. Lowe’s effect
The Lowe’s effect is a psychoacoustic effect in the stereo range. The Lowe’s effect reveals that if the delayed signal is inverted and superimposed on the direct signal, an obvious sense of space will be produced. The sound seems to come from all directions, and the listener seems to be in the band.
10. Keyhole effect
The mono recording and playback system uses a microphone for recording, the signal is recorded on a track, and an amplifier and a speaker are used for playback, so the playback sound source is a point source, just like the listener passes through the key on the door To listen to the symphony in the room, this is the so-called keyhole effect.
11. Bathroom effect
When you are in the bathroom, you have a personal experience. The sound in the bathroom has a long and excessive reverberation time. This phenomenon is called the bathroom effect in the sound quality description of electroacoustic technology. When the low and intermediate frequencies are exaggerated, there is resonance, the frequency response is not flat, and the 300Hz boost is excessive, the bathroom effect will appear.
12. Doppler effect
The Doppler effect reveals the relevant listening characteristics of moving sounds: when there is relative movement between the sound source and the listener, the tone of the sound determined by a certain frequency will change, and when the sound source approaches the listener When the frequency is slightly higher, when the sound source is gone, it is a slightly lower frequency. This change in frequency is called Doppler shift. The sound source that moves closer produces greater intensity at the same distance from the listener than when it does not move, while the sound source that moves away produces less intensity, usually the sound source is concentrated in the moving direction.
13. Li Kai test
Li Kai’s experiment proved that when the phases of the two sound sources are opposite, the sound image can go beyond the two sound sources, and even jump behind the listener.
The Li Kai experiment also suggested that as long as the intensity and phase of the two sound sources (left and right channel speakers) are properly controlled, a wide range (angle, depth) of the sound image moving field can be obtained.