At present, HD has become a popular element, HDTV, HD, HD cameras, HD camcorders, HD DV, etc., have been unknowingly integrated into our daily lives. As an important part of the home theater, the amplifier has to be upgraded to HD. At present, the products on the market are mainly divided into two levels, one is to support the next generation of high-definition power amplifier, and the other is the ordinary power amplifier of the DVD era. Of course, such classifications are not very scientific and complete, because of the wide variety of amplifiers, and this classification is only suitable for AV amplifiers.
In the face of the mixed products on the market, how should we choose? What are the main indicators? How to look at it? Below we will take the most common AV amplifier in the home theater as an example to explain, aiming to inspire others, I hope you can make a difference.
What is an AV amplifier?
AV amplifier, as the name suggests A (audio) means audio, audio, V (video) means audio, image, so AV amplifier is a collection of audio and video signal processing audio amplifier, mainly used to match the image source, produce audiovisual The effect of unity is to create a sound field as the main design purpose and is specially used for home theater. It controls the delay time between channels during playback through its internal delay and reverberation processing circuit, and simulates the sound field in various listening environments by adjusting the length of the delay time. The technical specifications of high-fidelity Hi-Fi amplifiers mainly include output power, harmonic distortion, signal-to-noise ratio, frequency range, rated impedance and damping coefficient, especially emphasis on harmonic distortion and signal-to-noise ratio; while AV amplifiers also have these Technical indicators, but more emphasis on channel isolation, delay time range, various sound field modes (DSP system, home THX system, Dolby AC-3 system) and other indicators.
Decoding format
At the heart of the home theater system is the surround sound system. With a surround sound system, you can achieve cinematic effects in your home. The surround sound system is a multi-channel playback system. There are many formats. Different formats have different characteristics. At present, the number of channels of the power amplifier is increasing, not only 5.1, 6.1, but also 7.1, 8.2, etc. We all know that 5.1 channel generally refers to Dolby Digital 5.1 and DTS5.1 two digital multi-channel surround sound audio formats. The 6.1 channel generally refers to the Dolby DigitalEX and DTSES digital multi-channel surround sound audio formats. This is based on 5.1, in order to make the left and right surround sound better connected and add a rear intermediate surround channel, which forms the 6.1 channel format.
As for the 7.1 channel, the THXSurroundEX system, Dolby also has DolbyProLogic IIx technology, which can separate 2-channel audio tracks into 7.1-channel restorations through complex matrix operations. THX is a certification standard for Lucas, not an audio format. When the 6.1-channel DolbyDigitalEX and DTSES came out, THX further evolved it into the THXSurroundEX system. In order to be compatible with the original two-way sound side channel and reinforce the surround sound surround feeling, then two rear channels are added on the basis of the original side channel, which constitutes 7.1 channels. Finally, the 8.2 channel currently uses a small number of products, it is to enhance the effect of the surround sound field, based on the 6.1 channel of Dolby DigitalEX and DTSES, added YAMAHA exclusive front surround channel (the Speaker box is placed in the main In the upper rear of the channel, a subwoofer output is added, and the rear intermediate surround sound is also expanded from one channel to two channels (similar to 7.1 channels).
All of these are various surround decoding format systems in the DVD era. It is obvious that the more channels you select, the more consistent the surround effect will be, and the stronger the surrounding feeling will be. In today's high-definition next generation, new-style amplifiers have new features and requirements. With the launch of Blu-ray and HD-DVD, a new generation of multi-channel surround sound formats have also emerged, including Dolby Digitalplus, Dolby TrueHD and DTSHD.
DolbyDigitalPlus (DD+) starts with 7.1 channels, and the sampling rate is expanded from the original DolbyDigital's 96-640 kbps to 32 kbps-6 Mbps, and it is developed for digital surrounds of up to 13.1 channels. Dolby TrueHD is based on MLP lossless technology and includes higher bitrate, additional channels, enhanced stereo mixing support, and extensive metadata capabilities such as dynamic range control and dialogue standardization. As for DTSHD, the 7.1 channel is used as the starting point, and the high bit rate of 1.5 Mbps or higher is supported. The sampling frequency is from 8-192 kHz (16/24 bit). Compared with the 768 kbps compression technology used in ordinary DVDs, the sound quality of DTSHD will be compared. Significantly improved. DTSHD's data traffic can be flexibly converted according to the required sound quality. With exclusive lossless compression technology, DTS compression is smaller and more detailed, providing higher quality sound recording and maximum 32-channel surround output.
Finally, the analog sound field that everyone often talks about, whether it is the DSP analog sound field advocated by YAMAHA or the exclusive DigitalCinemaSound of SONY, is the surround sound post-processing method of the space characteristics of the simulation institute and the concert hall. To compare the differences between the two in a sensory way, most people think that SONY's DCS pays more attention to the sound surrounding, while YAMAHA pays more attention to the open space. Both can be said to have their own strengths.
Power matching
The focus of the AV amplifier is to create an ideal listening environment with visual effects, creating a realistic sense of orientation, presence and shock. Therefore, the design focus of the AV amplifier is more concerned with the clarity of the dialogue and the large dynamic "burst" effect of the audio-visual environment, reducing or simulating the sound field positioning of the sound and picture, creating a variety of sound field atmosphere. In this way, not only the AV power amplifier frequency range is required to be as wide as possible, the distortion is small, the signal-to-noise ratio is high, the transient characteristics are good, the sound quality and the sound color are beautiful, and the sound pressure level is more emphasized: that is, under the premise of low distortion, the guarantee is ensured. Large enough output power.
The unit of output power of the power amplifier is watt (W). Since the measurement methods of different manufacturers are different, some names are different. For example, rated output power, maximum output power, music output power, peak music output power, etc. The rated power of the front-end main channel of the high-end AV amplifier is generally above 80W, to meet the requirements of the hospital's 107dB sound pressure level. However, some imported AV amplifiers, 5-7 channels, each channel total standard hundred W, the total power of thousands of W, but the power transformer is so big, I really do not know what power standard is used to calculate, Japanese AV The most obvious, always 6 people to swear, really calculated by 8 euros to have a full 100W (per channel is not bad). Anyone who has used AV amplifiers knows that when they are in a big dynamic, they tend to be soft. Therefore, it is recommended to buy AV amplifiers, it is best to choose the mid-range or above, otherwise it is similar to chicken ribs.
In general, the power of the amplifier is as large as possible. But the main function of the amplifier is to push the speaker, so it depends on the amplifier must match the speaker. However, there are many aspects involved in the configuration of the amplifier and the speaker. For example, the selection of the power amplifier grade, the choice of the power tube type, and the power amplifier of the low-sensitivity speaker are difficult to find a unified standard. It is worth noting that the general enthusiasts believe that the selection of the amplifier must be determined by the speaker, and there should be no concept of "power reserve" to configure the amplifier. The specific standard of power amplifier and speaker power configuration should be: under certain impedance conditions, the power of the amplifier should be greater than the power of the speaker, but not too large. The undistortion rate of the amplifier in general application places should be about 1.2-1.5 times of the rated power of the speaker; in the case of large dynamics, it should be about 1.5-2 times.
interface
Traditional home theaters are nothing more than signal transmission through optical, coaxial and RCA analog interfaces. For example, the previous DTS and Dolby codes transmit digital compression codes to AV amplifiers through optical fibers and coaxial interfaces. decoding. As the latest generation of digital interfaces, HDMI has been widely used in a variety of digital products, and with the HDMI interface began to be used in audio and video products and the maturity of technology, more and more power amplifiers have begun to use this theory without loss. The mode of transmission. And HDMI itself has passed three versions, HDMI's earliest interface specification HDMI1.0 was announced in December 2002, the current highest version is the HDMI1.3 specification released in June this year. Great attention should be paid to the difference, and their differences and applications are great. For example, technologies such as Dolby Digitalplus, Dolby TrueHD, and DTSHD can only be transmitted via the HDMI 1.3 interface, so you should pay attention when purchasing, and only the amplifier with this interface can enjoy the next generation of music.
The HDMI audio signal does not occupy an extra channel, but is combined with other auxiliary information to form a data packet, which is transmitted in the form of island data during the blanking period of the video signal transmission by using the three TMDS channels. It can provide up to 8 channels of high-quality audio signals with a sampling frequency of 192 kHz. In contrast, the four-channel signal of the CD audio system of 44.1 kHz and the latest DVD-Audio audio format of 96-kHz 6-channel signals are inferior. A lot.
Channel separation
Separation refers to the ability of a surround sound decoder in an AV amplifier to restore an audio coded signal to individual channel signals, and to the extent to which signals are "isolated" from each channel of the amplifier. The value is expressed in decibels (dB). The larger the dB value, the greater the degree of isolation between them. The mutual "crosstalk" of the sound between each channel restored by the amplifier is small, and the sound effect is better. Select AV amplifier, the larger the difference, the better, generally more than 60dB.
A power amplifier with poor resolution may have poor sound image localization, insufficient sound field, and poor sound image continuity. Higher channel separation is one of the prerequisites for accurate phase positioning. The high resolution allows the sound field to be expanded, resulting in a wider sense of space, while also making the sound positioning more precise and accurate. The high channel separation makes the instruments of music appreciation, vocal positioning, game sound positioning and film surround effects. Aspects have been strengthened. In short, the higher the resolution, the more impressive the sound field and the more precise sound positioning.
Signal noise ratio
SignalNoiseRatio is called the signal-to-noise ratio or signal-to-noise ratio. The unit is dB, which is the ratio of the useful signal output by the power amplifier to the unwanted noise. The current power amplifier SNR indicator is fully capable of coping with general music programs, so we should pay more attention to the background signal-to-noise ratio. Try to put the amplifier volume to the maximum and listen to the noise. Of course, the smaller the better. . If a amplifier has a high signal-to-noise ratio, it means that the background is quiet. Due to the low noise level, many details of the mute that are covered by the noise will appear, which will increase the floating sound, enhance the air feeling, and increase the dynamic range. Measure whether the signal-to-noise ratio of the amplifier is good or bad. There is no strict discriminant data. Generally, it is better than about 85dB. Below this value, it may be obvious in some music listening situations. The noise.
Delay time range
Anyone who has set up a home theater knows that when the surround sound box is placed in place, it is generally necessary to adjust the surround delay of the AV amplifier, so that the sound effects of the front and rear speakers are seamlessly integrated and perfectly integrated to obtain a satisfactory overall effect. This delay time range means that the adjustable speaker "delay" allows the processor to automatically compensate for room size. If the rear speakers are closer to the seat than the front speakers, and no short-term sound delay is added, the sound of the rear speakers will be heard before the front speakers, so to set the delay, you need to measure The distance from each speaker to the seat and enter these values ​​into the "Delay" settings section of the amplifier or receiver.
Today's receivers and amplifiers are available in meters or feet for accurate speaker delay calibration. However, some outdated equipment requires you to enter a millisecond delay value. To calculate these delays, use the following calculation method: First, measure the distance from the left front speaker to the seat. Then, measure the distance from the left rear speaker to the seat. You will get two numbers. These two numbers differ by 30 centimeters each, increasing the 1 millisecond delay. For example, the front speakers are 300 cm and the rear speakers are 150 cm, which is 150 cm apart, so the delay is 5 ms.
Frequency response
The frequency response indicates the consistency and sensitivity of the amplification of the signals of each different frequency when the amplifier amplifies the signals of different frequencies, also called the "frequency range". The wider the range, the more able to "care" the signals of more frequency components, the better the performance, it is very practical. Under normal circumstances, the audio signal that people can hear is about 20Hz~20kHz different frequency, different waveform, different amplitude change signal, so the amplifier should complete the amplification of the audio signal well, so the frequency response of the power amplifier should be at least It reaches 20Hz~20KHz. However, the overtones (harmonics) contained in the real music are likely to exceed this range. In addition, in order to improve the performance of the transient response, the amplifier is required to have a higher frequency range, and the current excellent power amplifiers generally do The range of 10 Hz to 100 kHz. For advanced imported power amplifiers, the low frequency can start from 0Hz (DC), because it is rare to work at full rated power. If the amplifier works normally, the frequency response must be very good, almost a straight line, usually far beyond Listening range (20-20KHz).
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