Listening, distinguishing, analyzing - sound quality and transient analysis

The standard definition and understanding of the terms "sound quality" and "sound effect" is difficult to have a unified standard, mainly relying on each person's own feelings. Therefore, it has led to endless debates. Based on my understanding of sound and player, and combining my own experience, the author puts forward the following points:


The so-called sound quality is the quality of sound and the quality of sound. The specific description of the sound includes audio, tone, tone and tone. If it is difficult to understand, you can use digital photos to compare.


If a photo is very pure in color, the level of detail is very rich, and the brightness is very accurate, we can say that the photo quality of this photo unit is very good. We can process the photos with the image processing software, which can deepen the color density, enhance the contrast, sharpen it, or add some artistic effects. So we look like the photo looks more beautiful, but it has actually destroyed the original image quality (note the cloud of the sky in the picture).


Listening, distinguishing, analyzing - sound quality and transient analysis

Before treatment


Listening, distinguishing, analyzing - sound quality and transient analysis

After processing


The second picture is decorated to look like a spring, but this is a photo taken during the winter.


The same is true for sound quality. We adjusted the equalizer to make the high and low sounds enhanced, plus the DFX plug-in and so on, which sounded more pleasant to us. In fact, many of the details of the sound have been lost.


Sometimes it is essential that we process and modify the sound or image so that it is more in line with the individual's appreciation needs. However, we don't want to improve the sound quality. In short, the more processing, the more plug-ins, the more damage to the sound quality.


Besides, many people are comparing the sound quality of the playback software. Comparison is not impossible, but you must know how to compare, otherwise it will only give people ignorance.


We generally add plugins more or less when listening to music, but in fact, at this time we are only comparing sound effects, not sound quality. If the effect of the sound effect is removed, we actually compare the decoder of the playback software. If the playback software of the same decoder is used, it is almost impossible to compare the differences. Even with different decoders, MP3 decoding is basically a very mature technology. Although there are differences, it is also very small. In our general player, claiming to be able to distinguish it is just self-deception. There is or does not know at all that it is only sound effects, not sound quality.


The main terms of sound quality evaluation are:


The sound is broken (劈): severe harmonics and intermodulation distortion, there is a “beep” sound, the flat top has been cut, and the distortion is greater than 10%.

The sound is hard: there are harmonics and intermodulation distortion, which is obviously measured by the instrument, and the distortion is 3% to 5%.

Sound explosion: There are too many high frequencies or medium and high frequencies, and there are two kinds of distortion.

Sound sand: medium and high frequency distortion, transient intermodulation distortion.

The sound is rough: there is distortion, slightly higher in the middle and high frequency, and there is transient intermodulation distortion.

The sound is stunned: the transient is not good, the resonance peak of the earphone speaker is prominent, and the low frequency or medium and low frequency is excessive.

Wide sound: frequency bandwidth, medium and low frequency, good low frequency, moderate reverberation.

The sound is boring: the high frequency or medium and high frequency is too small, or the directivity is too sharp and deviates from the axis.

The sound is slender: the high frequency or medium high frequency is moderate and the distortion is small, the transient is good, and there is no transient intermodulation distortion.

The sound has layers: the transient is good, the frequency characteristics are flat, and the reverberation is moderate.

Solid sound: good mid-low frequency, moderate reverberation, and loudness.

The sound is divergent: the intermediate frequency is lacking, the intermediate frequency transient is not good, and the reverberation is too much.

Narrow sound: narrow frequency characteristics, such as only 150Hz ~ 4000Hz.

Metal sound (lead skin sound): The high-frequency individual points are high and the distortion is serious.

The sound is round: the frequency characteristics and distortion indicators are good, the reverberation is moderate, and the transient is good.

The sound has moisture: medium and high frequency and high frequency are good, and the reverberation is enough.

The sound is bright: medium and high frequency and high frequency are sufficient, relatively flat, and the reverberation is moderate.

Sound spike: too much high frequency and medium and high frequency.

Treble whistle (floating): lack of intermediate frequency, medium and high frequency and high frequency pointing too sharp.

The sound is dark: lack of high frequency and medium frequency.

Sound dry: lack of reverberation, lack of medium and high frequency.

The sound is straight (wood): there is distortion, the middle and low frequencies have prominent points, the reverberation is less, and the transient is poor.

Sound balance (concord): good frequency characteristics and small distortion.

Booming: The resonance peak of the earphone speaker is seriously prominent, and the distortion and transient are not good.

The sound is clear: the medium and high frequency and high frequency are good, the distortion is small, and the transient is good.

The sound has a three-dimensional effect (in mono mode): the frequency response is flat, the reverberation is moderate, the distortion is small, and the transient is good.

The sound is transparent: the high frequency and the medium and high frequency are moderate, the distortion is small, and the transient is good.

The sound has a sense of presence (presence): the frequency response is good, especially the medium and high frequency is good, the distortion is small, and the transient is good.

Full of sound: frequency bandwidth, good mid-low frequency, moderate reverberation.

Soft sound (loose): low frequency and medium and low frequency, the distortion is small.

The voice is discouraged (potential), and the strength is good: the loudness is sufficient, the reverberation is good, and the low frequency and the medium and low frequency are good.


Transient

- the judgment of the sound


Judging whether the sound quality of the sound is excellent, transients are a very important indicator. Many audio equipment evaluations, especially for headphones and speaker evaluations, refer to a transient response or transient appearance. What is transient? What is the principle of transients? The author is here to discuss the issue of sound transients.


Transient refers to a short, explosive sound, and the sound of a timpani is an example of a musical transient. Transient is a concept that is closely related to time. It refers to a sudden change in signal strength. Often, these transient sounds are difficult to reproduce accurately.


Transient Response refers to the ability of a headset to accurately reproduce transient music changes. Transient response is the primary indicator of the ability of a headset to follow a burst of signal in music. The earphone with good transient response should respond immediately after the signal is sent, and the signal will stop when it stops, and it will never drag the water.


In the fever record, the percussion instrument, especially the drum music, and the symphony of the big scene lead to the transition part of the ensemble, the transient is very fast, this type of signal, for many headphones, is BT A signal is a signal that is difficult to restore.


The transient is not exactly equal to the transient or transient performance, transient response, refers to the headset system's ability to follow the abrupt signal. In essence, it reflects the high-order harmonic distortion of the pulse signal, which seriously affects the transparency and layering of the sound quality. The transient response rate V/μs is usually used. The higher the index, the smaller the harmonic distortion. For example, the conversion rate of a general amplifier is >10V/μs. In the digital signal, or record level, it is easy to turn the full signal into silence, and the square wave (such as drum sound and explosion sound) used in the test headphones is like this. Meaningfully, the playback of the headset. Only when the earphone can better express the transient signal can the evaluation of "transient performance be good" be given.


We often hear the word "transient distortion". What is transient distortion? The argument of the unreasonable head is that "the transient appearance is not good." Anything that cannot restore the original signal can be considered distortion. Including: the instant loudness is not good, the sound is broken, the percussion is delayed, or even a piece of mud, water and so on.


The main manifestation of transient response is transient distortion. Transient distortion is an important indicator of modern acoustics. It reflects the ability of headphones and amp circuits to keep track of transient abrupt signals, so it is also called transient response. This distortion makes the music lack of layering or transparency, and there are two forms of expression:


A: Transient intermodulation distortion


When a pulsed transient signal is input, the capacitance in the sound circuit prevents the output terminal from immediately obtaining the desired output voltage, so that the negative feedback circuit cannot obtain a timely response, and the ear is in an open loop state at this moment, so that the output is made. Clipping occurs in an instantaneous overload. This clipping distortion is called transient intermodulation distortion, and this distortion is more serious on the amplifier.


Transient intermodulation distortion is a dynamic indicator of the amp, mainly caused by deep negative feedback inside the amp. It is the chief culprit that affects the sound quality of the amplifier and leads to "transistor sound" and "metal sound." The main ways to reduce this distortion are:

Choose a good device and adjust the operating point to maximize the open loop gain and open loop frequency of the amp.

Strengthen the negative feedback of each amplification stage and cancel the negative feedback of each loop.


B: Distortion caused by too low conversion rate


As mentioned above, a high level input pulse causes the amp to clip and cause transient intermodulation distortion. So does the low-level input pulse cause distortion? This depends on the response time of the amp. Because the response time of the amp is too long, the change of the signal at the amp can not keep up with the transient distortion caused by the rapid change of the input signal, which is called the conversion rate is too low distortion. It reflects the response speed of the amp to the signal. This small amp with good distortion has good resolution, layering and positioning.


It is mainly caused by the fact that when a large transient signal is suddenly applied to the amp, the signal is distorted due to the slow response of the amp. Whether the envelope waveform of the amp output signal is similar to the input square wave waveform is generally used to express the following ability of the amp's transient signal. The distortion caused by the transient of the sound, mainly harmonic distortion, refers to causing the sound to be hard and fragile; and the steady-state or transient intermodulation distortion mainly causes the sound to be rough, sharp and turbid. Both of them degrade the sound quality, and if the distortion exceeds 3%, the sound quality is degraded. Headphones have the most distortion, and the minimum distortion is generally more than 1%.


End device

Impact on transient performance


The headphone amplifier is used for photoreaction and has a circuit unit with ultra-high magnification. It can be composed of discrete devices or implemented in semiconductor chips. With the development of semiconductor technology, most of the eardrums today are in the form of monoliths.


We often hear that a certain amp has a large conversion rate, a large conversion rate can better handle strong signals, and the signal is amplified in time, while a small conversion rate delays the sudden strong signal processing. It is good to have a large conversion rate. It is not the focus of this article. It is enough to understand that this parameter has some relationship with the transient.


Headphone speaker


A speaker is an electroacoustic device that converts an electrical signal into a sound signal. Specifically, the operation of the speaker is actually to convert a range of audio electric power signals into a audible sound with a small distortion and sufficient sound pressure level. There are many types of earphone speakers, and the classification methods are also varied. Generally, they can be classified according to their working principle and diaphragm shape.


Headphone speakers are the biggest bottleneck of transient performance, because to get the "transient performance" evaluation, this puts very demanding requirements on the control of the speaker. The means to ensure control is to increase this capacity, there are two ways - - One is to increase the magnetic density (for example: using a rare earth magnet, the rare earth magnet is 7 to 14 times the magnetic density of the ferrite magnet) or increase the magnetic volume (for example, increasing the magnetic steel).


In many books introduced by speakers, it is emphasized that the density of the diaphragm material is as small as possible, but I believe that the density of the diaphragm material is the most important, because the unit fo depends on the stiffness of the suspension system and the quality of the diaphragm. Lighter mass can get better transient response and dry high efficiency, but it has poorer low frequency performance. In addition, the too thin diaphragm will encounter the standing wave inside the earphone in actual use. Unnecessary distortion and abnormal peaks and valleys on the frequency curve are generated; the thicker diaphragm is the opposite, the transient response is compromised while getting more low frequencies, and the reduction in efficiency is accompanied by an increase in the power requirements of the ear room. However, it can be improved by designing the sound cavity of the earphone. Therefore, the author believes that the density of the diaphragm of the earphone speaker is a parameter that must be repeatedly considered, and it is necessary to select a diaphragm of appropriate density according to the actual use requirements.


This is not enough. "Transient performance is good" requires high-power amplifiers and power supply support. When the signal is rapidly increased, the peak power may be several times or even ten times the average power. Therefore, enthusiasts often use anti-aircraft guns to fight mosquitoes. The idea is to match the headphone amplifier, several medium power headphones with a few hundred watts of amp, an important reason for them to do this is - transient performance.


There are some differences in transient and transient performance. Some colloquial comments say that a headset is "transiently good" - it should be said that a headset has a good transient performance. The transient response earphone should be able to reproduce the transient of the music. From the clear click of the ring and the gong to the heavy plucking of the guitar, it should be both speed and accurate, neither rigid nor excessively flowing or slow dragging. The phenomenon.


After reading the introduction of the above knowledge, I must have a preliminary understanding of the sound quality and transient phenomenon of the sound. I hope that the shallow understanding of the author can help you to have a deeper understanding of the sound quality and sound effect of the sound.

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