This standard is a guide for listening tests of home radios and (or) recorders. It is applicable to listening tests of the sound quality of home radios and (or) recorders, and can also be used as a reference for listening tests of other similar home audio equipment. In this standard, listening tests are also called listening evaluations. GB/T 9375-1988 Listening Tests for Radios and Recorders GB/T9375-1988 Standard Download Decompression Password: www.bzxz.net

National Standard of the People's Republic of China
GB/T9375—1988
Listening tests on radio
receiver and/or tape recorder
Published on June 18, 1988
Implemented on December 1, 1988
Ministry of Electronics Industry of the People's Republic of China
National Standard of the People's Republic of China
Listening tests on radio
receiver and/or tape recorderGB/T9375—1988
This standard is a guide for listening tests on radio and/or tape recorder for home use. It is applicable to listening tests on the sound quality of home radio and/or tape recorder, and can also be used as a reference for listening tests on other similar home audio equipment. In this standard, listening tests are also called listening evaluations. Listening evaluations can adopt absolute methods and relative comparison methods. The absolute method refers to the comparison between the reproduced sound and the original sound. If the original sound cannot be obtained, high-quality professional equipment can be used to reproduce the sound, and the reproduced sound is used as the reference original sound. The relative comparison method refers to the comparison between the reproduced sound of the machine being listened to and the reference sample. The evaluation result of this method is easier to obtain good reproducibility. The reference sample should be selected very carefully because it is the basis for comparison and judgment. 1 Classification of the machine being listened to
1.1 Classification of radios
Stereo
Classification of recorders
FM/AM
FM/AM
Stereo
Pocket
Pocket
Portable
Portable
Combined
Combined
When conducting listening evaluation, the machines being listened to are generally classified according to the same level and type. Exceptions are also allowed for certain special purposes. Note: ① "" indicates the type of machine currently available in China. ② For dual-purpose receivers, the radio section is classified as a radio and the playback section is classified as a tape recorder. 2 Listening Room
2.1 Main Technical Performance
2.1.1 Dimensions: The values ​​given in Figure 1 indicate the permissible range of the dimensions of the listening room. The following values ​​are the recommended dimensions of the listening room. Volume V, 80m
Height H, 2.8m
Length L, 6.7m,
Width W, 4.2m.
Note: Existing listening rooms that do not meet this dimension should meet the technical requirements specified in 2.1.2 to 2.1.7 of this standard. Approved by the Ministry of Electronics Industry of the People's Republic of China on June 18, 1988 and implemented on December 1, 1988
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GB/T9375—1988
a. Plane schematic diagram
Figure 1 Listening room
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2.1.2 Reverberation time: Between 250 and 4000Hz, the average value of the reverberation time T60 at each point in the listening area should be within the range of 0.3~0.5s, and the measured value of T60 at each frequency point should not deviate from the average value by more than 25%. Below 250Hz and above 4000Hz, T6o is allowed to deviate from the above average value by more than 25%. However, below 250Hz, T60 should not exceed 0.8s. 2.1.3 The sound frequency response curve in the listening room should be as smooth as possible, without obvious sound coloration. 2.1.4 There should be no abnormal resonance and flutter echo in the room within the frequency range of 100-5000Hz. 2.1.5 When there is no listener, the background noise in the listening room should be less than 35dBA weighted, slow gear). The background noise value should be stated in the listening test result report.
2.1.6 Indoor lighting, color, seats, etc. should make the listener feel comfortable. 2.1.7 Indoor climate conditions:
Temperature: 18~35℃ (preferably 20℃);
Relative humidity: 25%~75%,
Air pressure: 86~106kPa.
Note: If the performance of the listening instrument and equipment is not affected and the listener does not feel uncomfortable, the climate conditions can be appropriately relaxed. In case of dispute, the provisions of 2.1.7 shall prevail.
2.2 Listening Room Layout
The listening room is recommended to be arranged as shown in Figure 1. This arrangement is applicable to both stereo and monophonic equipment. 2.2.1 The equipment to be listened to should be placed behind a sound-transparent curtain so that it cannot be seen by the listener. The curtain should be sound-transparent and light-proof, and the sound transmission loss within the audio frequency range should not be greater than 1dB (when measuring this sound transmission loss, the speaker and microphone are 2m apart and the curtain is placed in the middle). 2.2.2 The speakers of the equipment to be listened to should be placed in accordance with the manufacturer's technical specifications, but at least 1m from the side walls, at least 0.7m from the back wall, and at least 2m from the listener (1). These distances are measured from the speaker reference point. The position of a monophonic equipment can be adjusted within the above range. If the relative comparison method is used, the speakers should be at least 0.5m apart. The speakers of a stereo equipment should be placed symmetrically. If the relative comparison method is used for evaluation, the machine to be listened to and its reference model should be placed up and down as much as possible. For the speakers of the separate stereo equipment, the distance should be at least 2m. In a small listening room, the speakers may need to be moved to a distance of 20.5m from the side wall. Generally, the minimum listening distance should be 1.0 to 0.8 times the distance between the speakers, that is, the angle between the two speakers facing the listener (1) position is 55 to 65 degrees. 2.2.3 In the case that it does not conflict with the manufacturer's recommendations, the machine to be listened to should be placed on a solid support so that the reference axis of the speaker is located on a horizontal plane 1.25m above the floor of the room and points to the center of the listener's seat area. The directivity of the speaker after the directional placement should produce the widest discreteness of the sound in the horizontal plane passing through the reference axis. 2.2.4 The listener's position should avoid points with obvious peaks and valleys in the audio frequency response as much as possible. Each listener should be at least 0.4m away from the side wall and at least 1m away from the rear wall. The distance between listeners should be at least 0.6m. The backrest of the listener's chair should not be higher than the human shoulder. When evaluating the listening of stereo equipment, the main listener should be arranged on the axis of the stereo listening area, and the other listeners should be arranged as symmetrically as possible on both sides of the axis. If necessary, the listening position can be exchanged. 2.2.5 When measuring the listening sound level, the microphone of the sound level meter should be placed at the head position of the listener in position (1). The indoor layout should be stated in the listening test result report. 3 Requirements and connections of listening instruments and equipment
3.1 Listening evaluation of radio
3.1.1 The block diagram of listening evaluation of AM radio is shown in Figure 2.wwW.bzxz.Net
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Note: 1) If the program source and limiter can be reasonably matched, the mixing console can be omitted. 3.1.2 The block diagram of listening evaluation of FM radio is shown in Figure 3. !
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Note: 1) If the program source and limiter can be properly matched, the mixer can be omitted. If the stereo encoder contains pre-emphasis, the pre-emphasis device can be omitted. 3.1.3 The technical indicators of the listening instrument equipment should be higher than the technical indicators of the machine being listened to, so as not to affect the sound quality of the machine being listened to. The manufacturer and model of each equipment used should be stated in the listening test result report. 3.1.4 Modulate the high-frequency signal with the program specified in Chapter 4. Then couple the modulated signal to the machine being listened to via a loop antenna or other appropriate method.
For the amplitude modulation of the AM signal, for language programs, within the 1-minute test time, the maximum amplitude modulation value should be above 90%, and the amplitude modulation value should be maintained at above 70% for most of the time (more than 30 seconds). For music programs, within the 3-minute test time, the maximum amplitude modulation value should be above 80%, and the amplitude modulation value should be maintained at above 30% for most of the time (more than 90 seconds). The frequency deviation value and pre-emphasis characteristics of the FM signal should comply with the provisions of GB4312.1 "Technical Parameters and Measurement Methods for FM Broadcast Transmitters Mono and Stereo".
The input signal level AM should be 10mV/m. FM should be 70dBfl. The radio is tuned to the minimum distortion, and the modulation signal frequency is 1000Hz.
Note: 1) 1fw (10-15w) is 0dBf.
3.1.5 The performance of the reference prototype should be at the average level of similar machines being listened to. If for a specific purpose, a high-quality machine can also be used as a reference prototype. The condition of the reference prototype must be stated in the listening test result report. 3.1.6 The switching switch should be able to quickly switch between the reference prototype and the machine being listened to. The switching silence time should be less than 0.5s. No obvious interference sound should occur during the conversion. The connection from the power amplifier, the conversion switch to the speaker should be as short as possible. Its total resistance should not exceed 0.2Q or 1/40 of the nominal impedance of the speaker being listened to, whichever is smaller (the method of measuring the total resistance is: short-circuit the two terminals of the speaker, measure the total resistance of the power amplifier output end, including all switch contact resistances). 3.2 Listening evaluation of recorders
3.2.1 Listening evaluation of recorders includes playback evaluation and recording-playback evaluation. 3.2.2 Playback evaluation and recording-playback evaluation should be carried out under the same conditions. 3.2.3 The electrical and mechanical properties of the cassette tape used should be measured and meet the requirements for C-60, Class A specified in GB7309 "General Technical Conditions for Cassette Tapes", and should be stated in the listening test result report. 3.2.4 The selection of reference prototypes is the same as Section 3.1.5. 3.3 Stable conditions of power supply voltage and signal
Listening evaluation should be carried out under constant power supply voltage and constant signal strength. No interference signal should be felt in normal listening evaluation. If necessary, the influence of interference can be judged by a listening group. 4 Program source
4.1 Content
a. Language: male and female voices,
b. Music and opera: including piano music, string music, orchestral music, percussion music, electronic music, folk music, male and female solo, chorus, opera, etc.c. Natural sound;
d. Pink noise.
4.2 The duration of each section should be 20 to 40 seconds. After each section, a 5 to 15 second silent section should be left for scoring and writing comments. In the relative comparison method, the interval between each pair of programs should be 1 to 2 seconds. 4.3 The name and model of the program tape used should be stated in the listening test result report, and its objective technical indicators (dynamic range, frequency response, distortion, etc.) should be higher than the technical indicators of the machine being listened to. The festival tape used for evaluation should not have obvious sound quality defects. 5 Listeners
5.1 Listener conditions
5.1.1 The listener should be a representative of the user of the machine being listened to, and age, gender, hearing, and basic knowledge of original sound and music should be considered. 5.1.2 The hearing of the listener should generally be checked within the frequency range of 125 to 8000Hz, with a hearing level lower than 20dBHL1 (GB4854 "Standard Zero Level for Calibration of Pure Tone Audiometers"), and the hearing curves of both ears should be consistent. Although people with hearing damage exceeding the above range do not need to be excluded, their listening test results should be analyzed separately to see if they are consistent with the data of normal hearing personnel. In the case where the number of people in the listening group must be small, special methods can be used to select listeners. For example, the standard deviation of the person's previous listening test (a reliable test) can be used, or a listening test can be conducted to show that the person can: a. Discern a change of about 3dB in sound level and a 1% change in tone at 1000Hz. 4
GB/T9375—1988
b When pink noise is sent to a pair of speakers arranged in a regular stereo manner, the position of the resulting sound image can be accurately determined. Note: 1) dBHL represents the hearing level, with zero hearing level being 0dBHL. 5.1.3 For high-fidelity systems, it is also required that the listeners are experts, and more than half of the listeners have received music education. 5.1.4 For those who often participate in listening tests, hearing tests should be conducted regularly and files should be established. 5.2 Number of people in the listening group
During the formal listening test, the number of listeners each time is generally 410. If there are more than 10 people, the test should be conducted in groups. 5.3 Listening Panel Members
The gender and age composition of the listening panel members can be referred to Table 1. Table 1 Gender and Age Composition of Listening Panel Members Recommended Number of Listening Panel Members
Minimum
15~40 years old
40~60 years old
Above 60 years old
Recommended Number
The situation of the listening panel members (gender, age, occupation, hearing, etc.) should be stated in the listening test result report. 6 Listening Procedure
6.1 Volume Adjustment
The relative comparison method should be used to conduct listening evaluation when the volume of the machine being listened to and the reference sample is the same. Maximum
The sound level is measured using a pink noise signal, using the sound level meter specified in GB3785 "Electroacoustic Performance and Test Methods of Sound Level Meters", using the A-weighted curve and slow time constant.
The volume of the machine being listened to should be adjusted to the sound level that the listener considers satisfactory. The listening sound levels given below are for reference. Nominal useful power
0.5W
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