Mouse-type home answering machine

lorant

Mouse-type home answering machine [Copy link]

The fundamental reason why we have the ability to locate sound is that we have auricles. From the vibration of the sound source to the vibration of our eardrum so that we can hear the sound, I divide the sound propagation process into three steps: the first step is from the sound source to the eardrum, which is a monotonous process and the waveform does not change. The second step is that the sound wave passes through the eardrum and enters the external auditory canal, which is not a monotonous process and the sound wave waveform will be affected. This step is the key to sound localization and will be discussed in detail below. The third step is that the sound wave passes through the external auditory canal to reach the eardrum, causing it to vibrate and allow us to hear the sound, which is also a monotonous process.

Next, I will explain how we use the auricle to achieve sound localization.

If the sound source is on the left, the sound waves reach the left ear first and then the right ear, and there is a phase difference between the sound waves received by the two ears. Since sound waves lose energy due to the damping effect of air during propagation, the sound pressure on the left ear is greater than that on the right ear, and there is a sound pressure difference between the two ears. Since the sound waves need to bypass the skull, helix, tragus and other parts to reach the external auditory canal of the right ear, and do not need to bypass so many parts to reach the external auditory canal of the left ear, the high-order harmonic components in the sound heard by the right ear are less than those heard by the left ear, so there is a difference in the comprehensive waveform of the sound heard by the two ears. It is precisely because of these differences that we can judge whether the sound source is on the left or right.

Due to the different diffraction effects of the fundamental wave and harmonic waves in the sound wave, the shape of the auricle is complex and the reflectivity of the sound waves of each frequency is different, so the auricle will inevitably have different effects on the sound pressure, phase, etc. of the fundamental wave and each harmonic, changing the comprehensive waveform of the sound wave. If the sound source is in the front, the sound wave is reflected by the auricle into the external auditory canal; if the sound source is in the back, the sound wave bypasses the auricle and enters the external auditory canal. The front and back positions of the sound source are different, and the auricle changes the comprehensive waveform of the sound wave differently. Our brain can judge whether the sound source is in the front or back by analyzing and processing these "differences".

The principle and process of our recognition of the up and down directions of the sound source are basically the same as those of the front and back directions, except that some sounds may come from the top of the head, which assists in the recognition of the direction of the sound source.

In fact, our brain makes a comprehensive judgment based on the left, right, front, back, top and bottom directions of the sound source, and this judgment process is usually completed instantly. Therefore, when we hear a sound, we can usually quickly point out the direction of the sound source (but the bass positioning ability is poor).

There is no perfect thing in the world, and our ears are no exception. Although nature has given them the ability to locate sound images, it has not given them the ability to identify the distance of the sound source. This makes the world of sound we hear a world without a sense of distance, which is somewhat similar to the world seen by a one-eyed person.

There are certain connections between various disciplines. In astronomy, in order to study the positions and movements of celestial bodies, people assume that celestial bodies are distributed on a spherical surface with the observer as the center and an appropriate length as the radius. This spherical surface is called the celestial sphere.

Here, I borrow the idea of "celestial sphere": imagine a "sound field sphere", which is a sphere with the listener's head as the center and an appropriate length as the radius. All the sound sources around us are projected on the sphere, that is to say: the distance between each part of the sound source and the listener's head is considered to be the same, which is the radius of the "sound field sphere", and the three-dimensional sound source is considered to be a two-dimensional plane sound source. The basis for this is that our ears cannot identify the distance of the sound source, but can only identify the direction of the sound source, so the three-dimensional sound source can be abstracted into a plane, which is temporarily called a "surface sound source". Any sound we hear (except for self-generated sounds such as talking, breathing, tinnitus, etc.) can be considered to be emitted from "surface sound sources" distributed on the "sound field sphere".

Because the sound of each part of the "surface sound source" is different, for example, when we close the door with a "bang", the door's hinge side vibrates weaker, while the handle side vibrates stronger. For an idling car, its engine hood and front fender vibrate more strongly, while the trunk lid and rear fender vibrate less. ... Our auricles do not treat these differences in strength equally, so they can only be abstracted into sound-generating planes, and cannot be further abstracted into sound-generating points, that is, the "surface sound source" cannot be further abstracted into a "point sound source", otherwise it will be distorted. And because the sound sources in the real environment are mostly "surface sound sources" (for some very small sound sources, such as the sound source of cannons, they can be considered "point sound sources"), so if you want to perfectly reproduce the sound in the real environment, the key is to reproduce the "surface sound source".

To reproduce the "surface sound source" means that if we want to reproduce the sound of something, we have to make a flat model of the thing. To reproduce the sound of a train, we have to make a flat model of the train; to reproduce the sound of wind blowing through a tree, we have to make a flat model of the tree... and we have to precisely control the vibration of every point on these flat models, and we have to control the relative position of these flat models and the listener at any time... This is simply impossible. We can only rely on audio equipment to reproduce the sound in a real environment.

Looking at Hi-Fi audio equipment, whether it is the top reference box of Swans or the top turntable with a blue crystal cover, they cannot reach the true HIGH-END. Even if there is an absolutely perfect equipment, and there is no distortion in every link from recording to playback, it is impossible to reproduce the sound in the real environment well. The reason is: the vibration of each part of the diaphragm of the speaker is consistent (an ideal speaker does not have split vibration), and the diaphragm area is not large, which can only be equivalent to a "point sound source". According to theoretical analysis, there must be an infinite number of "point sound sources" to "piece together" a "surface sound source". In other words, there must be an infinite number of speakers to reproduce the sound in the real environment well, but a set of audio equipment has only a limited number of speakers, which means there are only a limited number of "point sound sources", and it is impossible to have an infinite number of speakers. Therefore, as long as the speaker is used for playback, no matter how large its dynamic range is, how wide its frequency response is, and how small its distortion is, it is impossible to reproduce the original sound in the real environment well.

At the beginning of this article, I mentioned that the auricle makes us feel that we are not as good as we used to be. The auricle is the key to our life. Since the emergence of 4.1-channel Dolby surround sound, 4.1-channel THX, 5.1-channel Dolby AC-3, 5.1-channel DTS, and the best 7.1-channel SDDS, humans have paid a high price, all because of the auricle! In order to avoid the trouble caused by the auricle, I have imagined a new way of recording and playing for personal listening: make a dummy head with a material of the same texture as human skin in real size. The key to making it is to accurately imitate the two auricles of a person. This will not be a difficult task for bionics. Then put two microphones in the external auditory canals of the two ears of the dummy head facing outwards. The sound pickup part of the microphone should be located at the opening of the external auditory canal and behind the tragus. Then put the dummy head in the environment where recording is required. The sounds picked up by the microphone are recorded on digital tapes, CDs and other media. Finally, the listener uses earplugs to replay these sounds.

The theoretical basis of this method is that the fake auricle will have a certain impact on the sound waves in the real environment, just like the real auricle. The microphone picks up these affected sound waves and replays them into the listener's external auditory canal through the medium of the earplug. The listener hears the sound affected by the accurately imitated fake auricle, which is no different from the sound affected by the real auricle. In addition, the propagation of sound waves in the external auditory canal is a monotonous process, and the waveform will no longer change. In addition, the external auditory canal is very narrow, and there is no difference between "point sound source" and "surface sound source" here, so the sound emitted by the earplug can still enable the brain to form a correct sound image positioning.

It is worth emphasizing here that the sound must be played with earplugs, because when listening with speakers or earphones, the listener's auricle will continue to affect the sound waves, making this recording method meaningless. The position of the microphone during recording is exactly where the listener puts the earplug, which is also to faithfully reproduce the original sound in the real environment. This recording and playback method can be figuratively regarded as extending the listener's auricle to the recording site, so there is a strong sense of presence, but there is still a flaw: it cannot reproduce the part of the sound in the real environment that is transmitted through the top of the head rather than the air, which will make the upper and lower position sense of the reproduced sound worse. The solution to this problem is: when recording, add a special microphone to the top of the dummy head. When playing, the listener has a special speaker like a small hat on his head to reproduce the sound at the top of the head. For ease of use, the top speaker and two earplugs can be connected into a whole with a bracket to become a pair of headphones or adopt some other installation form. As long as the listener can feel the sound coming from the top of the head, the specific form can be freely played by the headphone designer. If the listener does not have high requirements or this kind of headphones are not compatible with the current two-channel equipment, the overhead speakers can be omitted, but the sense of presence will be worse. In summary, this method of using a dummy head for recording, earplugs and overhead speakers for playback is completely possible to reproduce the sound in a real environment very well. Compared with the current popular surround sound equipment, this method has the following advantages:

1. Only one pair of headphones is needed, and the cost is much lower than a bunch of speakers.
2. The dynamic range, frequency response and other indicators of headphones can be made much higher than those of speakers, and there will be no drawbacks such as phase shift caused by the crossover.
3. Headphones only need very little power to drive, eliminating the need for multi-channel amplifiers and other equipment. And the performance indicators of headphone amplifiers can be made much higher than those of amplifiers.
4. Only three channels are needed at most, which is basically compatible with current equipment, and the additional investment is very small (it will be even better if you don't want to use overhead speakers).
5. There is no "emperor's seat" restriction. When you put on headphones, you are always in the "emperor's seat".

Under current circumstances, there are still some difficulties in realizing this recording and playback method:

1. Capacitor microphones are now mostly used for recording, which are too large to fit into a dummy head, and the sound quality of small resident microphones is not satisfactory.
2. It is difficult for a series of equipment from recording to playback to work well together, and their various distortions make it difficult to achieve a flat and smooth frequency response curve.
3. Although the performance indicators of headphones are much better than those of speakers, there are still harmonic distortion, subharmonic distortion, intermodulation distortion, transient distortion, etc. Although these distortions are very small, they are still hundreds or thousands of times larger than the distortion of the circuit, which reduces the performance indicators of the whole machine. I think that with the advancement of science and technology and the maturity of new technologies such as ion speakers, these difficulties will soon be solved. By then, listening to music with headphones will become the preferred way for personal listening with its unmatched advantages, because only headphones can make people feel like they are in the scene.