Sound quality evaluation

1. The main listening place for the audio in the listening room is indoors, and the home audio is the family housing. Professional audio requires a studio or recording room with certain acoustic requirements. A special listening room should be used for the evaluation and should be in the area It simulates the actual application environment, such as the listening environment of a typical family or the specific application place. Generally, family houses are limited by decoration and economic factors, and the room's acoustic characteristics cannot be in the best condition. From the perspective of listening evaluation, in order to facilitate the exchange of listening evaluation results, it is necessary to establish a dedicated listening room, focusing on the following five aspects.
1. Room size. The fundamental element of standing wave in a rectangular room is the ratio of length, width and height. If the size ratio is not suitable, peaks and valleys will be formed at some frequency points in certain positions in the room, causing audible acoustic staining. The recommended listening room volume is: 90-120m3 for mono programs and 120-150m3 for stereo programs; the optimal ratio of length, width and height is 1.0: 1.4: 1.9; also available is 1: 1.26: 1.59. If other ratios are used, the indoor resonance frequency should be calculated to avoid isolated, grouped simple harmonic motion and standing waves.
2. Reverberation time. The reflection sound and reverberation sound in the listening room have a great influence on the quality of the entire sound. The number, type and placement of sound-absorbing materials determine the indoor reverberation time (T) and the uniformity of the reverberation sound field, that is, the degree of diffusion. The measurement of the reverberation time should use the pink noise source, with the frequency point of 1/3 octave, in the absence of a listening person's empty field. According to the international standards, the uniformity of the reverberation time T and frequency is: Between 125Hz and 4kHz, the average value of T is between 0.25 and 0.45 seconds. The frequency characteristics should be flat or slightly longer at low frequencies and shorter at high frequencies, and the difference between the single measured value and the average value at each point within this frequency should not exceed 25 %; 0.35 ± 0.05 seconds within 125 ～ 165Hz; 0.3 ± 0.05 seconds within 200Hz ～ 4kHz, allowing T to deviate from the average value of the intermediate frequency by more than 25%. According to actual experience, if the listening room is mainly used for listening evaluation, the reverberation time is 0.3 to 0.4 seconds. The effect is better, not too short, otherwise it will make the sense of openness worse; if the reverberation time is too long, the sound image will be localized Not clear enough, but the sense of openness is better.
3. Transmission frequency response. After selecting the sound excitation point, sound source position and receiving point, that is, the position of the microphone or listening human ear, the unevenness of the amplitude-frequency response should be within the specified range. The measurement uses a sinusoidal signal, and a pink noise signal can also be used. To evaluate stereo products, the imbalance of the sound field (the symmetry value of the left and right channels) should be higher than that of the mono channel.
4. Environmental conditions. When there is no listening personnel in the empty field, the background noise in the listening area should be less than 25dB when the lights and air conditioning are turned on; and no more than 35dB when there are staff. There must be no low-frequency buzzing, high-frequency hissing, or trembling echoes in the room. When using a sound level instrument of more than 95dB within the frequency range of 100Hz ~ 5kHz at a distance of 1m from the sound source to measure the indoor environment, there should be no abnormal resonance and tremor echo. Since the reliability of the listening evaluation is greatly affected by the limit value of the environmental conditions, the ambient temperature is 15-30 ° C, preferably 20 ° C; the relative humidity is 25-75%; the air pressure is 360-1060Hg, the indoor lighting should be soft, do n’t Directly listen to the eyes of the person.
5. Hearing. Using a vocal and language program band corresponding to the purpose of the room, a group of trained evaluators will evaluate at the designated listening position. The results of listening evaluation should be determined and analyzed, and the defects caused by the acoustic conditions of the room or the electroacoustic system should be excluded. If necessary, the specific parameters of the actor's original sound can be evaluated.
2. Program selection There are two methods for selecting programs for listening evaluation: one is to select according to the characteristics of sound quality; the other is to select according to the main types of audio products. No matter which method is used, the following points should be considered.
1. Real and natural. The sound source of the program is real and natural, but it is not too much rendering. It is based on the principle of evaluating the sound quality of electro-acoustic products, and it does not excessively pursue a certain artistic effect.
2. Distinctive features. The sound quality should have more distinctive features, and the characteristics of each program are different from each other, so that there are many differences in the evaluation. The entire program should be able to basically assess the sound quality level of the electro-acoustic products, that is, the program materials cannot be randomly stacked, so that the evaluation It takes a long time, but there is very little information; it is also necessary to prevent incomplete materials, so that some sound quality can not be expressed.
3. Neutral feelings. Avoid choosing programs with too much "emotional color" to prevent affecting the psychological state of the sound quality assessors.
4. High visibility. Try to choose familiar works and more familiar actors and announcers. The audition program includes a variety of different types of languages, symphony orchestra, classical music, chamber music and songs, a variety of light music, including classical light music, folk music, dance and jazz music with and without vocal music, and a small number of musical instruments. Such as piano, violin and cello, wooden orchestral instruments, steel instruments, percussion instruments, solo and instrumental accompaniment.
5. Typical programs.
(1) Voice. The program time should not be too long, the voice can use male and female voice commentary. The tone of the female voice should be natural and intimate, the vowel sounds well in resonance, and it sounds strong and full; the male voice should be generous and rich.
(2) Piano solo. Optional the third movement of Beethoven's "Moonlight" Sonata for about 37 seconds. Including five 8 ° of the piano, the melody is smooth, the playing intensity fluctuates greatly, and basically shows the characteristics of the piano. The sound is strong and elastic, harmonious and clear, and the crawl from low to high increases the color of the program.
(3) String ensemble. Optional first movement of Mozart's "Serum of Strings", time 48 seconds. The playing skills are skillful, clean and unified, the sound of each part in the violin is real, the characteristics are distinctive, the natural balance is good, there is a strong overall sense, harmony and beauty.
(4) Woodwind quartet. The first movement of the wood quartet of Jean Francais can be selected. The program time is 37 seconds. This is a typical chamber music work, in which the flute, clarinet, oboe, and big pipe sounds natural, the real, balanced spectrum tone, and the sound of keystrokes and ventilation are clearly discernible, which also increases the characteristics of chamber music.
(5) Brass wind. Optional Tchaikovsky Symphony No. 1 movement, program time 38 seconds. The performance scene is grand, it sounds high and thick, the horn at the beginning is far away and not falsified, the trombone coming in is majestic and powerful, and the trumpet is crisp and soft.
(6) Orchestral music. Optional Musolski composer, Ravel's "Picture Exhibition", the program time is 1 minute and 6 seconds. Performed by a large symphony orchestra, it is magnificent and has a strong sense of listening. All sounds are vivid and natural, especially the timpani sound is solid and powerful, the army drums are thick, and they are shocking.
(7) Unaccompanied chorus. Optional song "Singer is singing more and more love", the program time is 40 seconds. The voices are bright, beautiful and round.
(8) Female soloist. Choosing the song "On the Field of Hope", the program time is 1 minute and 2 seconds. The voice is crisp and sweet, and the words are natural and clear. The folk singing method is used to enhance the intimacy of the song.
(9) Male solo. Choose the song "Chao Feng Feng", the program time is 53 seconds. The sound is more relaxed and natural, and the classical style of accompaniment and singing is stronger.
(10) Folk music ensemble. Selected song and dance "Silu Flower Rain", time 47 seconds. The ethnic style is very strong, various musical instruments are real and pleasant, the sound of the drum is relaxed and soft, the sound of the flute is crisp and cold, and the stringed and plucked instruments are also distinctive and full of vitality.
(11) Percussion. Time 40 seconds. The percussion methods of various musical instruments are realistic, the sound features are sufficient, and the sound image is real.
(12) Electronic synthesis fragments. Time 54 seconds. Using typical electronic music, the sound is loud and active, making a moving sound image interspersed in the middle, enhancing the vivid interest.
(13) Peking Opera version. Choose "Anti-Sippi Little Open", the time is 1 minute and 8 seconds. The level is clear and clean, Jinghu's voice is real but not hairy, the percussion sound is round and not broken, the plucked sound is clear and true, and the sound image positioning is stable and clear.
(14) Peking Opera Dao Bai. Select "Thirteen Sisters", the program time is 51 seconds.
(15) Peking Opera singing. Select "Li Qingzhao", time 1 minute 6 seconds. The horns are round, beautiful and soft.
(16) The steam locomotive passes through the fork crossing. The time is 51 seconds, showing the sound of a row of trucks passing through the fork. From far to near, the wind is fast and electric, giving people a sense of immersion. Due to the full load, the sound of the file clanging at the interface of the rails is particularly prominent.
(17) Bells. The time is 30 seconds, the impact characteristics are bright, the sound is solid and powerful, the aftertones are slowly and evenly decayed, and there are weak human voices and bird and insect sounds, which make the environment natural and real.
Liu Leiwen excerpted from "Beijing Electronics" var check_allow = "/d/Api/iscantalk.html"; var add_url = '/ d / article / write /'; function CheckLogin () {now_uid = ''; var ElecfansApi_checklogin = '/ webapi / passport / checklogin'; var logout_url = "{: U ('Login / logout')}"; var logout_url = 'http://bbs.elecfans.com/member.php?mod=logging&action=logout&refer=front'; $ .get (ElecfansApi_checklogin, function (data, textStatus) {if (data! = "") {EchoLoginInfo (data); CheckEmailInfo (data); data = $ .parseJSON (data); now_uid = data.uid; / * var login_content = 'write an article