Acoustic principles related to timbre

- Nov 08, 2019-

It's obvious that sound doesn't produce light, so we can't receive optical signals directly from sound; although sound is a kind of vibration, there is no other place on our whole body that can receive sound signals effectively except eardrum. So sound doesn't produce tactile sensation, let alone dry and wet.

So, why can sound give people the feeling similar to vision and touch?

It says that sound is the vibration of air. This kind of vibration becomes a one-dimensional vibration after finishing the ear canal, because our eardrum has only one degree of freedom. The back and forth vibration of the eardrum is amplified by the leverage of three small ossicles and then transmitted to the cochlea. The cochlea converts this pulse into an electrical signal. After the electrical signal is transmitted to the auditory system, the neural network interprets it as useful information and ignores useless information

However, there are horizontal differences between people on how to interpret the one-dimensional pulse signals of these time domains. We call this process auditory cognition, which can be roughly divided into three levels:

Low level: This is the basic level. From the ear to the auditory center, the basic physical characteristics of sound signal amplitude and frequency are first perceived. The amplitude here is not only the size of the sound, but also the perception of the "waveform"; and the frequency here is not only the pitch, but also the perception of the timbre. Regarding the lower level cognition, the difference between people is relatively small.

Mid level: with the basic materials collected by the bottom cognitive, we can further interpret and understand the voice. In the range of middle-level cognition, we can interpret different amplitudes and frequencies as symbolic contents such as voice, musical instrument and rhythm. What we often call "Solfeggio and ear training" is actually the middle-level cognitive ability. Therefore, in the middle level of cognition, the difference between people is greater, because it is usually related to training and experience.

High level: middle level cognition provides the interpretation of sound content. Then these contents will trigger some stress reactions. A typical stress response is emotion. For example, if you hear soothing music, you will also feel your blood pressure drop; if you hear the praise from the leaders, you will be happy and tears will come to your eyes. As for the cognition of senior management, the difference between people is further widened.

Sound makes a person sound bright, or feel dry or wet, which can be explained as follows:

Bright or dim: obviously, this feeling occurs in the middle and upper cognitive range. On the one hand, although there is a difference in the acoustic energy between some different chords (for example, the big triad is usually louder than the small triad), the small triad played hard and the big triad played lightly still sound brighter than the latter. So this is not a phenomenon that the underlying perception can explain. The sense of chord listening is largely determined by experience. Every time your music teacher plays these two chords to you, he uses the word "bright and dim"; every time you watch a movie or TV, the bright pictures are often matched with "bright" chords, and so on These life experiences teach you how to distinguish between bright and dim chords (or timbre), forming stereotypes in your mind.

On the other hand, in the music of our world, the trend of major chords often indicates a satisfactory solution; at the same time, the timbre of high-frequency energy concentration often represents the role of "positive energy". These impressions in the scope of high-level cognition are actually connected with our bright and bright high-level cognition in the visual world - although different senses are in different physical world, they share emotions and emotions in the scope of our high-level cognition, otherwise we are not a complete person.

The picture above is a very simple schematic diagram of cognitive level. For example, you can understand it as follows: for example, when you see a comet falling on the ground on the road, first you see its image, hear its voice, and feel a kind of heat radiation on your skin at the bottom. Then, in a very short period of time, your middle-level cognition understands the combination of these three signals into the same event (this step is called multisensory integration, very important), and then Report to the senior management for cognition; * this matter only enters into the life of "you" as a "person" and causes you to have complex emotions. Although these three cognitive levels have chronological order, they also interact with each other to a certain extent. For example, if you see comets coming, the middle level may let you run, but the top level says to look again, so you can feel that your legs don't know whether to listen or not.

Dry or wet: this concept is actually understood by people who understand a little acoustics. It refers to the ratio between direct sound (also called dry sound) and reflected sound in a place (usually indoor) or a recording. If there is only direct sound, such as the middle and high frequency sound in the anechoic room or the room surrounded by sound-absorbing materials, which does not sound reverberation, it is "dry" sound; otherwise, there will be a lot of reverberation in the bathroom or the new room without furniture, which is "wet" sound. The so-called dry and wet is a simplified word used by acoustics workers to describe the reverberation ratio of a sound.

For a long time, some people can really feel a sound that makes their ears dry, or sweaty palms wet. However, this experience is also different from person to person. Similarly, this can also be explained by the above figure: the middle and high-level perception of sound and the middle and high-level perception of dry and wet share part of the neural network in some areas. Or, maybe you can't associate like this before, but from today on, after reading this answer, you will gradually establish this connection