14 laws of audio technology

There are 14 laws in audio technology. Do you know what they are?

1. Subjective feeling in frequency domain

The most important subjective feeling in the frequency domain is pitch. Like loudness, pitch is also a subjective psychological quantity of hearing. It is the attribute 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 pure sound, while the latter is the pitch of complex sound such as music. The pitch of complex sound is not just the frequency analysis, but also the function of the auditory nervous system, which is affected by the listener's listening experience and learning.

2. Subjective perception of time

If the duration of a sound exceeds about 300ms, the increase or decrease in the duration of the sound will have no effect on the change in the threshold of hearing. The perception of pitch is also related to the duration of the sound. When the duration of a sound is very short, no pitch can be heard, only a "click" sound can be heard. The duration of the sound is longer before the pitch can be felt. Only when the sound lasts for more than tens of milliseconds can the perceived pitch be stable.

Another subjective characteristic of the time domain is echo.

3. Subjective perception of the spatial domain

Human ears have obvious advantages over listening with one ear. They are highly sensitive, have a low threshold, have a sense of direction to the sound source, and have a relatively strong 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 located inside the head. In order to distinguish these two senses of space, the former is called directional and the latter is called positioning.

4. Weber's Law of Hearing

Weber's law shows that the subjective perception of sound by the human ear is proportional to the logarithm of the objective stimulus. When the sound is low, the increase in the amplitude of the sound wave will increase the volume of the subjective perception of the human ear; when the sound intensity is high, the increase in the volume of the subjective perception of the human ear will be small when the amplitude of the sound wave is increased.

According to the above-mentioned listening characteristics of the human ear, an exponential potentiometer is required to be used as a volume controller when designing a volume control circuit. In this way, when the potentiometer handle is rotated evenly, the volume increases linearly.

5. Ohm's Law of Hearing

The famous scientist Ohm discovered Ohm's law in electricity, and he also discovered Ohm's law in human hearing, which reveals that human hearing is only related to the frequency and intensity of each partial tone in the sound, but has nothing to do with the phase between the partial tones. According to this law, the control of the recording and playback processes in the sound system can ignore the phase relationship of the partial tones in the complex sound.

The human ear is a frequency analyzer that can separate the harmonics in a complex sound. The human ear has a high sensitivity to frequency resolution. In this respect, the human ear has a higher resolution than the eye. The human eye cannot see the various colored light components in white light.

6. Masking effect

Other sounds in the environment can reduce the listener's hearing of a certain sound, which is called masking. When the intensity of one sound is much louder than another sound, when it is loud enough and the two sounds exist at the same time, people can only hear the louder sound and cannot perceive 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 sound is greater than that of high-frequency sound.

This auditory characteristic of the human ear provides important inspiration for designing noise reduction circuits. When playing a tape, we have such a listening experience: when the music program is changing continuously and the volume is loud, we will not hear the background noise of the tape, but when the music program ends (blank tape), we can feel the "hiss..." noise of the tape.

In order to reduce the impact of noise on program sound, the concept of signal-to-noise ratio (SN) was proposed, which requires that the signal strength is sufficiently greater than the noise strength so that the listener will not feel the presence of noise. Some noise reduction systems are designed based on the principle of masking effect.

7. Binaural Effect

The basic principle of binaural effect is this: if the sound comes from the front of the listener, the distance from the sound source to the left and right ears is equal, so the time difference (phase difference) and timbre difference between the sound waves reaching the left and right ears are zero, and the sound is felt to come from the front of the listener instead of to one side. When the sound strength is different, the distance between the sound source and the listener can be felt.

8. Haas Effect

Haas's experiment proved that when two sound sources sound at the same time, the feeling of binaural listening is different depending on the delay between one sound source and the other sound source. It can be divided into the following three situations to explain:

(1) When the time delay between one of the two sound sources and the other is within 5 to 35 ms, it is as if the two sound sources have merged into one. The listener can only sense the existence and direction of the leading sound source, but cannot sense the existence of the other sound source.

(2) If one sound source is delayed by 30 to 50 milliseconds from another, the presence of both sound sources can be felt, but the direction is still determined by the leading sound.

(3) If the delay of one sound source is 50ms greater than that of another sound source, the two sound sources can be felt to exist simultaneously. The directions are determined by each sound source, and the delayed sound is a clear echo.

The Haas effect is one of the foundations of stereo system directionality.

9. The de Boer Effect

The De Boe effect is another basis for the orientation of a stereo system. The De Boe effect experiment is: place two speakers for the left and right channels, and the listener listens on the symmetry line between the two speakers. Feed different signals to the two speakers, and you can get the following conclusions:

(1) If the same signal is fed to the two speakers, that is, the intensity difference ΔL = 0 and the time difference Δt = 0, only one sound is felt, and it comes from the symmetry line of the two speakers.

(2) If the intensity difference ΔL between the two speakers is not zero, the sound will feel like it is coming from the louder speaker. If the intensity difference ΔL is greater than or equal to 15 dB, the sound will feel like it is coming entirely from the louder speaker.

(3) If the intensity difference ΔL = 0, but the time difference Δt between the two speakers is not 0, the sound will feel like it is moving towards the speaker that arrived first. If the time difference Δt is greater than or equal to 3ms, the sound will feel like it is coming entirely from the direction of the speaker that arrived first.

10. Lowe's Effect

The Lowe effect is a psychoacoustic effect in stereo range. It reveals that if the delayed signal is superimposed on the direct signal in reverse phase, a distinct sense of space will be generated, and the sound seems to come from all directions, and the listener seems to be in the band.

11. Keyhole Effect

A mono recording and playback system uses one microphone to record the signal on one track, and uses one amplifier and one speaker for playback, so the reproduced sound source is a point sound source, just like a listener listening to a symphony in a room through the keyhole in the door. This is the so-called keyhole effect.

12. The Bathroom Effect

When you are in the bathroom, you will have a personal experience that the sound emitted 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. The bathroom effect occurs when a certain section of the low and mid-frequency is exaggerated, there is resonance, the frequency response is uneven, and the 300Hz boost is excessive.

13. Doppler Effect

The Doppler effect reveals the listening characteristics of moving sounds: when there is relative motion between the sound source and the listener, the sound determined by a certain frequency will feel that its pitch has changed. When the sound source approaches the listener, the pitch is slightly higher in frequency, and when the sound source moves away, the pitch is slightly lower in frequency. This frequency change is called the Doppler shift. The intensity of a moving sound source is greater than that of a stationary sound source at the same distance from the listener, while the intensity of a moving sound source is smaller. Usually, the sound source is concentrated in the direction of movement.

14. Li Kai Experiment

Li Kai's experiment proved that when the phases of two sound sources are opposite, the sound image can extend beyond the two sound sources and even jump behind the listener.

Li Kai's experiment also suggests that as long as the intensity and phase of the two sound sources (left and right channel speakers) are properly controlled, a sound image movement field with a wide range (angle, depth) can be obtained.