[Home theater network hdav.com.cn] Preface: In the audio-visual system, only the words 'like' can't be explained. The rest are the contents of electroacoustics, coding, and signal science. There is nothing to explain, only us. Do not understand. After reading it carefully, follow up and learn, you are no longer a novice!
This article will explain our replay system from the electrical, acoustic and coding, signal and other subjects, what is the matter, no longer vague, clear.
---------------------------- Speaking from the principle of equipment ----------------- ----------
Recently, it has been inexplicably pulled into some Q groups, forums, and various clouds. It has been found that many players are burning equipment, but they are negligent in understanding the basics. Another type of player is an art interpretation technique with a thick layer of metaphysics. Technology is technology, technology is art service, but not art. Replay is not art, just technology, creation is art, music concert? Adaptation meeting? Concert? No, you say art, you are at most Call appreciation art, don't confuse when discussing. Don't get old, it's the best in art, the best in art, actually...., back to the topic, this post, the subject of technology, art is subjective, can only be impossible to say.
Audio playback structure points: source, decode, zoom, speaker.
ã€source】
All kinds of turntables, CDs, network machines, hard drives, and optical drives are all sources, and the function is to deliver digital audio data. Some people say that the disc is different from the network machine. The disc uses the unevenness of the coating on the disc to record the data, and the hard disk uses the magnetic record data. What is the difference? Of course, there are differences. You bought a poor quality disc and the coating is uneven.
In fact, the impact of the source is the largest in the system, otherwise why is the THD the highest? The output is digital data, this is no difference, but the output is a big problem. SPDIF, HDMI is the main means of source output, including USB, etc., SPDIF has two physical modes: coaxial, optical fiber (fiber has conversion module). There is a saying: the number, the clock is playing, it is too accurate. Students who have studied signal processing should know that serial processing relies on the high frequency of the clock. Each square wave change causes a data transmission. The serial number of these digital serial ports is the clock and the instability of the clock. It is the biggest challenge of source signal output, we call it Jitter (clock jitter). Jitter is inevitable and can only be minimized. Remember that OPPO has become a high-priced machine after being changed by a certain price brand? One of the important changes is to adjust the circuit and replace the crystal oscillator. The jitter indicator is better than before. In the high-frequency digital circuit, lowering the jiiter may require multiple times. Double the time and cost.
The format of the source. PCM and DSD. PCM is pulse coded and DSD is density coded. PCM is high frequency sampling, absolute precision recording, DSD is ultra high frequency sampling (64 times of CD, called DSD64), 1 bit relative accuracy recording. CD, DVD-A, BD-A, etc. are all PCM formats, and SACD is DSD format. The PCM sampling is generally high, the CD era is 44.1k (the human ear resolution is 20 times that of 20kHz), the precision is 16bit, and now the high is 384k (all are multiples of the 48K in the DVD era, the 44.1K of the CD has been eliminated), 24bit. DSD now has DSD512. Relative recording is actually the process of converting precision processing into sampling density. The higher the density, the higher the precision. The closer the density is, the closer the precision changes to the original waveform. It is similar to Tesla's unified field theory, electricity and magnetism. Hahaha.
Keywords: turntable, optical disc, hard disk, PCM, DSD
ã€decoding】
Decoding this thing, the player is most confused. AC3 is called decoding, DTS is called decoding, and DAC is also called decoding... In fact, decoding two words means relative to coding. AC3, DTS, including the current HD format, is a technology patent. They encode multi-channel data in time-division, and then calculate it in real time through its own (or authorized or certified) decoder chip to separate the channels. This process is called decoding. But this code can't be enlarged yet, and the digital signal is decoded.
DAC, digital to analog conversion. This is also called decoding in HiFi players. As far as analog is concerned, as long as it is a number, they think it is encoding, and right.
Therefore, the word decoding has its own language environment, different environments and different meanings. In AV, decoding is multi-channel encoding for channel separation. In HiFi, decoding is digital-to-analog conversion. Of course, the AV also has to perform digital-to-analog conversion, and the decoded I2S data is sent to the DAC for digital-to-analog conversion. The DAC comes out of the analog waveform.
Keywords: decoder, DAC
ã€enlarge】
Amplification is the process of amplifying the decoded weak signal to a high-power signal that can push the speaker body to work.
In fact, friends who have had DIY know, or friends who know some electricity, look at the data of the DAC and know that the DAC is an analog signal. This signal is very weak, very...
Earlier friends, exposed to tape drives, vinyl machines, the magnetic induction of the magnetic head, the vibration of the mechanical head, the signal is weaker, more...
From here, the analog signal is very weak at first, what should I do? Don't be too busy, zoom in on this matter, it is about matching, the amplifier parts have the best working area, the circuit equipment has impedance, and the formulas U2/R, I2/R begin to exert their power.
A weak signal, first need to carry out voltage amplification, with voltage amplifier components (op amp, tube), you see the output of those outputs 2.1v, this is not the original, this is the amplified voltage, the initial voltage may Only 0.21V or even smaller. With this voltage, the latter device can be driven. This is called: preamplifier voltage amplification, referred to as the preamp!
With this voltage, it may not be enough, the latter device will re-amplify the voltage to a stable value, so that the power-amplified device can amplify the current (U*I=W) because the power amplifier component (transistor, electron tube) is opposite to the voltage. It is required. If this voltage is not reached, the device will not work happily. This process is called: post-stage power amplification, referred to as the post-level!
Therefore, the front and rear levels are the concept. Before the advent of AV, the potentiometer was used in the front stage to control the volume. AV also used this structure, so many people said that "the front level can be controlled." Before you started, you can understand it. See here, You understand, so don't say that anymore. AV's predecessor, it seems that there is no accurate definition, it should mean .... decoder + preamplifier.
[speaker]
The current that drives the speaker is current! Remember this! Because the current stage is the voltage regulator!
Speakers, designers have different debugging, have produced different styles, are liked by different people, this is subjective, it seems to be also non-quantitative things, that is, many players say: cultural connotation. This varies from person to person, don't live in your own cover.
But as a product, the speaker is a technical product with its product parameters, such as frequency response, total harmonic distortion (THD), impedance.... We cannot use culture to measure this. If you have to use culture to measure these parameters, I can only say: Are you very cultural? Have you seen a few books in European masterpieces? Will you compose music? Can ink paintings be held? Will you dance ballet? By, don’t play metaphysics, We can also be friends.
Say the speaker, first of all, if the parameters are not reliable, don't look at it, even the parameters are inaccurate, what do you still do speakers? For example, don't give THD, don't give frequency response
Speaking of speakers, we have to mainly talk about matching, matching is mainly impedance matching. The speaker has three parameters: sensitivity, impedance, THD, sensitivity and THD are often contradictory, sensitivity represents the efficiency of electroacoustic conversion, and this is often entangled with fidelity, there is a saying: the higher the efficiency, the harder the fidelity . Although not necessarily completely accurate, I personally want to say that it makes sense! Otherwise, those boxes with high efficiency and low distortion will not sell so expensive!
The impedance of the speaker has a close relationship with the latter. The impedance of the speaker is not a fixed value, but a curve related to the frequency of the sound. The impedance has the lowest value at low frequencies, as low as 2 ohms or less, and then gradually increases, sometimes as large as 10-20. Europe. Is there any problem? Well, the problem is very big! U2/R = W, the impedance is small, the output power is large, right, the low-impedance speaker will make the transistor amplifier power become bigger, 8 ohms 100W, 4 ohms become 200W, You think you earned, but don't forget, the amplifier has power limitation, it will be distorted. Once overloaded, the crystal machine clipping distortion is very serious....., do you think that a small Japanese computer with a 400W desktop sound? You need to know the good post-level 400W, maybe you can't move alone.
Impedance and amplifier. There is no transistor in the amplifier, because the amplifier has an output transformer. The internal resistance of the amplifier is very large. It needs to be stepped down to the load output. If there is no such transformer, the load will not get any power, but just this transformer makes the amplifier The power does not change with the impedance curve of the speaker, but the problem is not here. The problem is the current! When the impedance of the speaker is very small, U=IR knows that I want to get bigger, the amplifier is a high-voltage low-flow device, can not withstand I .
See here, you know what box is equipped with an amplifier, or what kind of power should the amplifier reserve? Don't forget to look at the impedance curve and the value on the curve to compare what your amplifier can provide.
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