In the face of a speaker, how to evaluate its sound quality is good or bad? This is a lot of audio and video enthusiasts difficult to grasp. Sometimes, we will encounter a situation, the same speaker, different people will give different sound quality evaluation. Then, does the industry have a set of subjective evaluation criteria, and there is no relevant standard at present. But we can try to rigorous, scientific methods to carry out subjective evaluation of sound quality. Below, the author will introduce some relevant knowledge of subjective evaluation of sound quality.
For audio equipment or cinema systems, their sound cannot be fully measured using parameter indicators. The subjective evaluation of audio equipment is the evaluation of the characteristics of the equipment by listening under the condition that the environment and the program can be controlled. Moreover, it is often difficult to make a subjective evaluation of only a single device, so it is usually standard equipment or comparison between multiple devices to obtain a comprehensive effect of loudness, frequency range, tone balance, spatial distribution, quality and non-uniformity.
Conditions for subjective evaluation of 1. sound quality
The evaluation of sound quality depends on a variety of factors, such as sound source characteristics (sound pressure, frequency, spectrum, etc.), signal characteristics of audio equipment (such as distortion, frequency response, dynamic range, signal-to-noise ratio, transient characteristics, stereo separation, etc.), sound field characteristics (such as direct sound, early reflection sound, reverberation sound, interaural correlation number, reference vibration, sound absorption rate, etc.), auditory characteristics (such as loudness curve, audible range, various hearing senses), etc.. Therefore, this requires the evaluator to listen to various sound effects in a relatively standard environment.
Selection of (I) Signal Sources and Program Materials
Different program sources will have a great impact on the evaluation results when evaluating sound quality. Therefore, the program sources for sound quality evaluation should not only be systematic and comprehensive, including music and voice of different genres and styles, but also have strict recording and production requirements to ensure sufficient frequency band and amplitude.
(II) with current high-performance system equipment
When listening to a certain audio equipment, the sound playback or pickup system must be composed of the product and other audio equipment. Due to the rapid development of the audio industry, different equipment in addition to the objective indicators have obvious differences, its own inherent "timbre", so there is no so-called "standard sound". This requires that the current equipment be selected as much as possible in the subjective listening evaluation to reduce the introduction of additional influencing factors to the subjective evaluation. Now there are many manufacturers in the world to launch the "reference level" products, although it can not be said that these products have reached the ideal level, but their excellent performance, enough to be used as standard equipment.
(III) meet the acoustic requirements of the listening room
There is no doubt about the influence of listening environment on sound quality. Due to the different structure, shape, volume and internal surface sound absorption treatment methods of different listening rooms, the acoustic parameters of the room are different. In this way, the same audio products in different rooms listening evaluation will draw different conclusions. Therefore, certain acoustic conditions should be standardized for the listening room used in the listening evaluation to reduce the influence of the listening room on the evaluation results. In addition, the listening room should have the appropriate temperature, humidity, light, to prevent these factors affect the mood of the audition personnel.
(IV) requirements for sound quality assessment personnel
Because the sound quality evaluation has a strong personal subjective color, the individual differences in the occupation, physiology, emotion and cultural accomplishment of the listener directly affect the evaluation results of sound quality. Therefore, in the subjective evaluation of sound quality of audio products, the selection of members of the audition group is very important. The members of the audition group not only have high requirements for the sensitivity of the hearing itself (referring to the conditions possessed by the human ear itself), but also have the ability to evaluate the aesthetics of sound quality and the sound quality of musical instruments and other sound sources. At the same time, but also through the sound quality evaluation can be related to the objective technical indicators of audio products, when the product has a slight difference in sound quality, listen to what kind of sound source to distinguish, with what attributes to judge the sound quality difference.
In order to minimize errors in the evaluation of sound quality due to individual differences among auditees, an audition group may include scientific and technical workers engaged in stereo and architectural acoustics, electro-acoustics and acoustics, recording and tuning technicians, as well as musicians, music editors and film and music directors and actors.
2. subjective sound effects
Generally, various attributes of sound quality are subjectively evaluated according to the changes and combinations of the three elements of sound, namely loudness, pitch, and timbre, such as low-frequency loud for full sound, high-frequency loud for bright sound; low-frequency weak for smooth sound, high-frequency weak for clear sound. Below we will combine the sound source, sound field and signal characteristics, to introduce several typical hearing.
(I) three-dimensional sense, telepresence
Sound not only has the level, has the direction, and has the space sense. The sound image orientation of various sound sources is accurate and clear, and there is a complete sound image group distribution. The sound distortion is small, the dynamic range is large, and the transient response is good, giving people an immersive feeling.
(II) intimacy, natural feeling
The sound changes naturally and smoothly, the loudness, tone, reverberation and balance are appropriate, without exaggeration. The momentum, style and dynamic range conform to the natural characteristics of the sound source, making people feel cordial, natural and pure and beautiful.
(III) sense of the whole, sense of group
Refers to the frequency is rich and coordinated, the low frequency is thick and strong, the high frequency level is clear, the overall momentum is magnificent and delicate, the dynamic range is large and smooth, just like the group peak stands and gives people the overall aesthetic feeling.
(IV) integration, balance, harmony
Under the conditions of wide frequency response, low distortion, high signal-to-noise ratio and large dynamic range, the sound volume, tone uniformity and reverberation of each part of the singing or band are relatively harmonious and balanced, and the whole sound field is organically integrated.
In addition to the above several kinds of hearing, we in the subjective evaluation of the sound, but also found that the sound has the following obvious performance:
Refers to the language has a good understanding of the music level. When the balance condition and the sound transient characteristics are not good, the low sound and the reverberation sound are too heavy, etc. will bring the feeling of "fuzzy" and "turbid.
It refers to the proportion of each part of the program coordination, high, medium and bass with proper. There is often an imbalance in the work itself or in the orchestra, which can be balanced by tuning and picking up.
Refers to the integration of sounds, especially the rich middle and low overtones, and the high overtones are not too prominent. The response is appropriate, the hearing is warm, thick and elastic. High signal level is not necessarily plump, poor transient response, high loss of low-order overtones, weak mid-bass, insufficient reverberation sound, improper time delay of early reflection, etc. may all bring the feeling of thin and dry defects.
Beautiful and beautiful, shiny without sharp noise. It is mainly used to evaluate vocals and musical instruments. Excessive treble, obvious distortion, and poor acoustics in the hall may make the sound rough.
Refers to the high middle tone full, sounds clear, active. Pre-reflected sound, reverberation sound and direct sound blend properly, can increase the brightness. Only focusing on increasing the sound pressure level of the direct sound may not be effective.
Soft-sharp and hard
The sound is loose, not sharp, and has a comfortable and pleasant feeling. If the pickup distance is too close, it will affect the diffusion of sound, and the sound will be sharp and hard.
Maintain the characteristics of the original sound source. When tuning, the unpleasing sound will be suppressed, or the sound source will be modified to make efforts in the direction of pleasing to the ear, but the characteristics of the original sound must not be deformed, so that the original piano into a black tube. This is not only the evaluation of the terms must be included, but also the principle of playback sound.
The meaning of 3. commonly used listening evaluation terms:
Sound breaking (splitting): serious harmonic and intermodulation distortion, with "poof" sound, flat top cut, distortion greater than 10%.
Hard sound: lack of bass, more medium and high frequencies, too short and too fast harmonic decay at high frequencies, short low-frequency reverberation, obvious intermodulation distortion, and poor transient response.
Sound burst: high frequency or medium frequency too much, there are two kinds of distortion.
Sound sand: the passband distortion is large, there are additional higher harmonics, and accompanied by transient distortion.
The sound is muddy: the transient is not good, the speaker resonance peak is prominent, and the low frequency or medium and low frequency are too much.
Sound wide: frequency bandwidth, low frequency, good low frequency, moderate reverberation.
Sound stuffy: high frequency or medium and high frequency is too little, or the directivity is too sharp to deviate from the axis.
Fine sound: the sound energy density is small, the loudness is not enough, the sound is fine and weak, the lack of low frequency, medium and high frequency and high frequency, the reverberation sound is insufficient.
There are levels: good transient, flat frequency characteristics, moderate reverberation.
Sound solid: good low frequency, moderate reverberation, loudness enough.
Sound divergence: intermediate frequency is lacking, intermediate frequency transient is not good, and reverberation is too much.
Narrow sound: the frequency characteristics are narrow, the high and low ends are lacking, the frequency band is not wide, the reverberation is short, and the intermediate frequency is too prominent.
Metal sound (lead skin sound): in the high frequency individual point prominent high, serious distortion.
Sound mellow: good frequency characteristics, minimal distortion, moderate reverberation, good transient.
There is moisture: medium and high frequency and high frequency is good, reverberation is enough.
Bright sound: medium and high frequency and high frequency enough, relatively flat, moderate reverberation.
Sound spike: high frequency and high frequency too much.
High-pitched virtual (floating): lack of intermediate frequency, medium and high frequency and high frequency pointing too sharp.
Dark voice: lack of high frequency and medium and high frequency.
Sound dry: lack of reverberation, lack of medium and high frequencies.
Balanced or Concorde: Good frequency characteristics and low distortion.
Roar: The speaker resonance peak is seriously prominent and the transient is not good.
Good clarity: medium and high frequency and high frequency, small distortion, good transient, moderate reverberation
Three-dimensional sense (in mono mode): flat frequency response, moderate reverberation, good transient.
Transparency: distortion is very small, transient response is good, wide and uniform frequency response, medium and high frequency and high frequency out, reverberation sound is appropriate.
Sense of scene or presence: frequency response and transient are good, especially in the high frequency is better.
Plump: frequency bandwidth, good medium and low frequency, moderate reverberation.
Soft (loose): low frequency and medium and low frequency, sound relaxation, appropriate loudness, reverberation sound slightly larger, distortion is small.
Have boldness of vision (potential) and good strength: sufficient loudness, good reverberation, good low frequency and medium and low frequency.
Conclusion: Subjective evaluation of speakers can only form an objective and true subjective evaluation by comparing and judging more than one in a controllable environment and program sources.