2. Subjective perception of the time domain <br> If the length of the sound exceeds approximately 300 ms, then the increase or decrease in the length of the sound does not contribute to the threshold change of the hearing. The feeling of tone is also related to the length of time of the sound. When the sound lasts for a short time, you can't hear the tone, just hear the "squeaky" sound. The duration of the sound is lengthened to have a feeling of tone. Only when the sound lasts for more than tens of milliseconds, the perceived pitch can be stabilized, and another subjective characteristic of the time domain is the echo.
3. The subjective feeling of the spatial domain The human ear has obvious advantages over the binaural listening. It has high sensitivity, low listening valve, a sense of direction to the sound source, and strong anti-interference ability. In stereo conditions, the sense of space obtained by listening to speakers and listening to 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 located inside the head, in order to distinguish between the two. The sense of space, the former is called orientation, the latter is called positioning.
4. Weber's Law of Hearing <br> Weber's Law shows that the subjective feeling of human hearing is proportional to the logarithm of objective stimulus. When the sound is small and the amplitude of the sound wave is increased, the subjective feeling volume of the human ear is increased by a large amount; when the sound intensity is large and the same sound wave amplitude is increased, the subjective feeling volume of the human ear is increased less.
According to the above listening characteristics of the human ear, an exponential potentiometer is required as a volume controller when designing the volume control circuit, so that the volume is linearly increased when the potentiometer is rotated uniformly.
5. Ohm's Law of Hearing <br> The famous scientist Ohm discovered the Ohm's law in electricity, and he also discovered the Ohm's law of the human ear. This law reveals that the hearing of the human ear is only related to the sounds of the sound. The frequency is related to the intensity and is independent of the phase between the partial sounds. According to this law, the control of the recording, playback, and the like in the sound system can not consider the phase relationship of each of the partial sounds in the complex sound.
The human ear is a frequency analyzer, which can separate the homophonic sounds in the polyphony. The sensitivity of the human ear to the frequency is very high. At this point, the human ear has higher resolution than the eye, and the human eye cannot see various kinds of white light. Colored light component.
6. Masking effect <br> Other sounds in the environment can cause the listener to reduce the hearing of a certain sound. This is called masking. When the intensity of one sound is much larger than the other, when the two sounds are both large and the two sounds exist at the same time, one can only hear the sound of the sound, but not the other. The amount of masking is related to the sound pressure of the masking sound, and the sound pressure level of the masking sound increases, and the masking amount increases. In addition, the masking range of the low frequency sound is larger than the masking range of the high frequency sound.
This auditory characteristic of the human ear provides an important inspiration for designing noise-reducing 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 noise floor of the tape, but when the music program ends (blank tape), we can feel it. The "å’..." noise to the tape exists.
In order to reduce the influence of noise on the sound of the program, the concept of signal-to-noise ratio (SN) is proposed, that is, the signal strength is required to be sufficiently larger than the noise intensity, so that the listening does not feel the presence of noise. Some noise reduction systems are designed using the principle of masking effects.
7. Binaural effect <br> The basic principle of the binaural effect is this: if the sound comes from the front of the listener, the time difference between the sound source reaching the left and right ears due to the equal distance of the sound source to the left and right ears (phase Poor), the timbre is zero, and the sound is heard from the front of the listener instead of being biased to one side. When the sound is different, you can feel the distance between the sound source and the listener.
8. Haas effect <br> Haas's test proves that when two sound sources are simultaneously sounded, the feeling of binaural listening is different according to the difference of the delay time of one sound source and the other sound source, which can be divided into two parts. The following three situations are explained:
(1) When the delay time of one sound source and the other sound source 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 the sound source of the previous one. Existence and direction do not feel the existence of another sound source.
(2) If one sound source delays another sound source 30~50mS, the existence of two sound sources can be felt, but the direction is still determined by the predecessor.
(3) If the delay of one sound source is greater than 50mS of the other sound source, the simultaneous presence of the two sound sources can be felt, the direction is determined by each sound source, and the hysteresis sound is a clear echo.
The Haas effect is one of the foundations of stereo system orientation.
9. Lloyd's effect <br> The Lloyd's effect is a psychoacoustic effect of the stereo range. The Lloyd's effect reveals that if the delayed signal is re-inverted and superimposed on the direct signal, it will produce a distinct sense of space. The sound seems to come from all directions, and the listener seems to be in the band.
10. Keyhole effect <br> The mono recording system uses a microphone to record, the signal is recorded on a track, and one amplifier and one speaker are used for playback, so the sound source is a point source, just like listening. Listen to the indoor symphony through the keyhole on the door, which is the so-called keyhole effect.
11. Bathroom effect <br> There is a personal feeling when you are in the bathroom, the sound in the bathroom, the reverberation time is too long and excessive, this phenomenon is called the bathroom effect in the sound quality description of electro-acoustic technology. When the low and medium frequency segments are exaggerated, there is resonance, the frequency response is not flat, and the 300Hz boost is excessive, the bathroom effect will occur.
12. Doppler effect <br> The Doppler effect reveals the listening characteristics of moving sounds: when there is relative motion between the sound source and the listener, it will feel that the sound determined by a certain frequency has changed its pitch. When the sound source approaches the listener, it is a slightly higher frequency tone, and when the sound source leaves, it is a slightly lower frequency tone. The amount of change in this frequency is called the Doppler shift. The moving sound source is greater at the same distance from the listener than when it is not moving, and the removed sound source produces less intensity, usually the sound source is concentrated toward the moving direction.
13. Li Kai test <br> Li Kai test proves 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 listening sound.
The Li Kai test also suggests 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.
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