1. Subjective perception in the frequency domain

An important subjective sense in the frequency domain is pitch. Like loudness, pitch is a subjective psychological quantity of hearing, which is a property of hearing to judge the pitch of a sound. The difference between pitch in psychology and scale in music is that the former is the pitch of a pure tone, while the latter is the pitch of a compound sound like music. The pitch of a compound sound is not simply a matter of frequency resolution, but is also a function of the auditory nervous system and is influenced by the listener's listening experience and learning.

2. Subjective perception of the time domain

If the duration of a sound exceeds approximately 300 ms, then an increase or decrease in the duration of the sound does not play a role in the threshold change of hearing. The perception of pitch is also related to the duration of the sound. When the duration of the sound is very short, no tone is heard, only a "click". Only when the sound lasts for more than tens of milliseconds can the perceived pitch be stabilized, and another subjective perceptual property of the time domain is echo.

3. Subjective perception of the spatial domain

The human ear has obvious advantages over monaural listening with binaural hearing, with its high sensitivity, low listening valve, sense of direction to the sound source, and relatively strong anti-interference ability. In stereo conditions, the spatial sense obtained by listening with speakers and with stereo headphones is not the same, the former hears the sound seems to be located in the surrounding environment, while the latter hears the sound positioned inside the head, in order to distinguish between these two spatial senses, the former is called orientation and the latter is called localization.

4. Weber's Law of Hearing

Weber's law shows that the amount of subjective perception of the human ear listening to sound is proportional to the logarithm of the objective stimulus. When the sound is small and the amplitude of the sound wave is increased, the subjective perceived volume of the human ear increases by a large amount; when the sound intensity is large and the amplitude of the same sound wave is increased, the subjective perceived volume of the human ear increases by a small amount.

According to the above characteristics of the human ear, the volume control circuit design requires the use of an exponential potentiometer as the volume controller, so that when the potentiometer handle is rotated evenly, the volume is increased linearly.

5. Ohm's law of hearing

The scientist Ohm discovered Ohm's law in electricity, and he also discovered Ohm's law in human ear hearing, which reveals that human ear hearing is only related to the frequency and intensity of each component of the sound, but not to the phase between the components. According to this law, the control of the recording and playback processes in the audio system can be done without considering the phase relationship of each component of the complex sound.

The human ear is a frequency analyzer that can separate the harmonics in the complex sound. The human ear has a high sensitivity to frequency discrimination, and at this point the human ear is more discriminating than the eye, which cannot see the various colored light components in white light.

6. Masking effect

Other sounds in the environment can make the listener hear a sound less, which is called masking. When the intensity of a sound is much larger than another sound, when the large degree and the two sounds exist at the same time, people can only hear the sound of the presence of the loud, and do not perceive the presence of another sound. The amount of masking and masking sound pressure, the sound pressure level of the masking sound increases, the amount of masking increases. In addition, the masking range of low frequency sound is greater than the masking range of high frequency sound.

This auditory characteristic of the human ear provides important inspiration for the design of noise reduction circuits. Tape playback, there is such a listening experience, when the music program in a continuous change and sound, we will not hear the background noise of the tape, but when the music program is over (blank section of the tape), you can feel the tape "sibilance ......" noise exists.

为了降低噪声对节目声音的影响，提出了信噪比（ＳＮ）的概念，即要求信号强度比噪声强度足够的大，这样听音便不会觉得有噪声的存在。一些降噪系统就是利用掩蔽效应的原理设计而成的。

7. Binaural effect

The basic principle of the binaural effect is this: if the sound comes from the front of the listener, at this time, because the distance from the sound source to the left and right ears is equal, so that the time difference between the sound waves arriving at the left and right ears (phase difference), the timbre difference is zero, at this time the sound is felt from the front of the listener, rather than favoring a certain side. The distance between the sound source and the listener can be perceived when the sound strength is different.

8. Haas effect

Haas's experiment proves that when two sources of sound are heard at the same time, according to the amount of delay between one source and the other, the perception of the two ears is different, and can be divided into the following three cases to illustrate:

(1) one of the two sources of sound and the other source of sound delay amount within 5 ~ 35mS, as if the two sources of sound into one, the listener can only feel the presence and direction of a sound source ahead of the other source of sound, do not feel the presence of another source.

(2) If a sound source delayed another sound source 30 ~ 50mS, can feel the presence of two sources, but the direction is still determined by the front guide.

(3) If a sound source delay is greater than another source for 50mS, the simultaneous presence of two sources can be felt, the direction is determined by each source, the lagging sound is a clear echo.

Haas effect is one of the basis of stereo system orientation.

9. The Rauch effect

The Rauch effect is a psychoacoustic effect of the stereo range. Rao's effect reveals that: if the delayed signal is then superimposed in reverse on the direct signal, it will produce a distinct sense of space, the sound seems to come from all directions, as if the listener is in the orchestra.

10. Keyhole effect

Mono recording system using a microphone recording, the signal recorded on a track, playback using an amplifier and a speaker, so the playback of the sound source is a point source, as the listener through the keyhole on the door to listen to the symphony in the room, which is the so-called keyhole effect.

11 Bathroom effect

When you are in the bathroom there is a personal feeling, the sound emitted in the bathroom, the reverberation time is too long and excessive, this phenomenon in the electroacoustic technology of the sound quality description called bathroom effect. When the low and medium frequencies are exaggerated in a section, there is resonance, frequency response is not flat, 300Hz lifting excess, the bathroom effect will occur.

12. Doppler effect

Doppler effect reveals the relevant listening characteristics of moving sound: when there is relative motion between the sound source and the listener, will feel a frequency determined by the sound of its pitch has changed, when the sound source to the listener close to a slightly higher frequency tone, when the sound source away is a slightly lower frequency tone. The amount of change in frequency is called the Doppler shift. The sound source moving closer to the same distance from the listener than when not moving to produce the intensity of the larger, and move away from the sound source to produce the intensity of the smaller, usually the sound source to move to the direction of concentration.

13. Li-Kai test

Li Kai test proves that: when the phase of the two sources is opposite, the sound image can be beyond the two sources, and even jump to listen to the sound behind.

Li Kai test also suggests that as long as the appropriate control of the two sources (left and right channel speakers) intensity, phase, you can get a wide range (angle, depth) of the sound image moving field.