Introduction to audio electrical performance testing of set-top boxes, DVD players, etc.

    With the development of technology, audio and video products (such as set-top boxes, DVD players, etc.) are also constantly updated, and people's requirements for their performance are getting higher and higher. Here we briefly introduce the electrical performance test items and methods of the audio part of audio and video products.

    Brief introduction of main test items:

    1. Audio output level: refers to the level value of the left and right channels measured under the condition that the output waveform is not distorted when the device is playing back.

    2. Audio amplitude response: The frequency range of the audio equipment when it is playing back and the relationship between the amplitude of the sound wave and the frequency. Generally, this indicator is tested with a frequency amplitude of 1KHz as a reference, and the frequency amplitude is expressed in decibels in logarithms. The overall frequency response of the audio system is theoretically required to be 20-20KHz.

    3. Audio signal-to-noise ratio: The so-called audio signal-to-noise ratio refers to the ratio of the sound system's playback of the sound source software to the new noise generated by the entire system. The noise mainly includes thermal noise, AC noise, mechanical noise, etc. This indicator is generally tested in decibels (dB) of the logarithmic ratio of the rated output power of the playback signal to the system noise output power when there is no signal input. The signal-to-noise ratio of a general audio system must be above 85dB.

    4. Audio distortion plus noise: An ideal amplifier should amplify the input signal and faithfully restore it without any change. However, due to various reasons, the signal amplified by the amplifier is often distorted to varying degrees compared with the input signal. This distortion is distortion. Expressed as a percentage, the smaller the value, the better. The total distortion of a HI-FI amplifier is between 0.03% and 0.05%. The distortion of the amplifier includes harmonic distortion, intermodulation distortion, crossover distortion, clipping distortion, transient distortion, transient intermodulation distortion, etc.

    5. Dynamic range: The so-called dynamic range refers to the logarithm of the ratio of the maximum undistorted output power of the sound system during playback to the system noise output power during static state, in decibels (dB). Generally, the dynamic range of a good sound system is above 100 (dB).

    6. Channel imbalance: Stereo balance refers to the difference in gain between the left and right channels in a stereo playback system. If the imbalance is too large, the stereo image positioning of the reproduced stereo will be offset. Generally, the stereo balance of a high-quality audio system should be less than 1dB.

    7. Left-right channel crosstalk: Separation refers to the degree of isolation between the left and right channels in a stereo sound system. It actually reflects the degree of crosstalk between the left and right channels. If the crosstalk between the two channels is large, the stereoscopic sense of the reproduced sound will be weakened, which can also be called crosstalk.

    8. Crosstalk between channels: The audio isolation between the sources actually reflects the degree of crosstalk between the audio sources. This is called crosstalk between channels.

    9. Noise floor: The noise output amplitude of the device when there is no audio.

    10. Maximum power: When the device is playing back, adjust the volume so that the waveform is as accurate as possible without distortion, which is the maximum swimming power output by the device.

    11. Channel phase difference: The phase difference of the signal output by the left and right channels of the device at the audio output end.

    12. Frequency error: the difference between the input signal and the output signal frequency.

    Regarding the method flow of audio electrical performance testing, we introduce the test process of left and right channel crosstalk below:

    ① First, we build a test system. The equipment used is an audio analyzer. The test sound source files are 0dB-1KHz left channel sine wave standard signal and 0dB-1KHz right channel sine wave standard signal. The connection method is as shown in the figure below.
                   

    ② Set the relevant parameters of the audio analyzer, the EUT plays the 0dB-1KHz left channel sine wave standard signal of the audio source file, and then read the value of Channel R on the audio analyzer, which is the L→R crosstalk value;

    ③ Follow the same steps as above, but change the sound source file to a 0dB-1KHz right channel sine wave standard signal, and read the value of Channel L, which is the R→L crosstalk value.

    The test methods of other audio projects are not described here one by one. If you need more information, please contact the relevant engineers of Chengdu Moore Laboratory.

    The test methods discussed in this article are mainly applicable to products with audio playback functions, such as MP3 players, MP4 players, repeaters, CD players, VCD players, DVD players, TV sets, home theaters, notebooks, etc.