The performance of the overall technical indicators of the sound system depends on the performance of each unit. If the technical indicators of each unit in the system are high, the overall technical indicators of the system are very good. There are six main technical indicators: frequency response, signal to noise ratio, dynamic range, distortion, transient response, stereo separation, stereo balance.

 

Frequency response

 

The frequency response refers to the frequency range at the time of playback of the audio equipment and the variation of the amplitude of the sound wave with frequency. Generally, this indicator is referenced to the frequency amplitude of 1000 Hz, and the amplitude of the frequency is expressed in decibels (dB) in logarithms.

The overall frequency response of the sound system is theoretically required to be 20 to 20000 Hz. In actual use, due to the structure of the circuit, the quality of the components, etc., it is often impossible to achieve this requirement, but generally it must reach at least 32~18000Hz.

 

Signal to noise ratio

 

The so-called signal-to-noise ratio refers to the ratio of the sound reproduction of the sound system software to the new noise generated by the whole system. The noise mainly includes thermal noise, alternating current noise, mechanical noise and the like. This indicator is generally used to indicate the nominal output power of the playback signal in decibels (dB) of the logarithmic ratio of the system noise output power at the time of no signal input. The signal to noise ratio of a typical audio system needs to be above 85dB.

 

Dynamic Range

 

The dynamic range is the logarithm of the ratio of the maximum undistorted output power to the system noise output power during static playback, in decibels (dB). Generally, the sound system with better performance has a dynamic range of 100 (dB) or more.

 

distortion

 

Distortion refers to the change of some parts (waveform, frequency, etc.) of the original source signal after the sound system plays back the sound source signal. There are mainly the following distortions of the sound system:

a. Harmonic distortion: The so-called harmonic distortion means that the sound after playback of the sound system has many extra harmonic components than the original signal source. This additional harmonic component signal is the frequency multiplication or frequency division of the source frequency, which is caused by the nonlinear characteristics of the negative feedback network or amplifier. The harmonic distortion of a hi-fi system should be less than 1%.

b. Intermodulation distortion: Intermodulation distortion is also a kind of nonlinear distortion. It is that two or more frequency components are mixed in a certain proportion, and each frequency signal is mutually modulated, and a newly added nonlinear signal is generated through the playback device, and the signal is generated. Includes the sum and difference signals between the individual signals.

c. Transient distortion: Transient distortion, also known as transient response, is mainly caused by the fact that when a large transient signal is suddenly applied to the amplifier, the signal is distorted due to the slower reflection of the amplifier. Generally, after the input square wave signal passes through the sound emitting device, the envelope waveform of the output signal of the amplifier is observed to see whether the input square wave waveform is similar to express the followability of the amplifier to the transient signal.

 

Stereo resolution

 

Stereo separation represents the isolation between the left and right channels in a stereo system, which actually reflects the degree of crosstalk between the left and right channels. If the crosstalk between the two channels is large, the stereoscopic effect of the reproduced sound will be weakened.

 

Stereo balance

 

The stereo balance indicates the difference between the left and right channel gains in the stereo playback system. If the imbalance is too large, the panned pan position will be shifted. The stereo balance of a typical high quality sound system should be less than 1 dB.

 

The meaning of dB

 

The unit of dB is a very widely used electronic method. It is a relative unit for measuring and comparing the power, voltage and current of a system. Later, due to advances in science and technology, it was recognized that human response to sound was changed in a logarithmic law, so that one unit was Bell, the name of the inventor of the telephone. The expression is: Bel = lg (P / Po) P is the measured power Po is the reference power: Bel represents the base 10 logarithm. In fact, it is found that Bel is too large, so take its tenth as a new unit, that is, decibel (dB) divides Bel by 10 is the dB expression: dB=10lg(P/Po), dB=20lg(E/Eo ), dB = 20 lg (I / Io).