Here I would like to write a special article for "decoders" to talk about what I think is basic, and some of the most common misconceptions.
In fact, from the beginning, the "decoder" often said by enthusiasts is a wrong name. The correct name should be "digital-to-analog converter". The English language is digital to analog converter, abbreviated as dac. There is no concept of "decoding" here, but rather the conversion of a digital signal to an analog signal. The so-called "decoder", the Dolby surround sound decoding used in av, that is decoding, but the concept of DAC is "conversion", not decoding. However, the use of the word decoder to represent dac has long been a convention, so everyone can understand it.
Since today is the era of digital audio, in fact, all the "sound replays" we use in our lives are all digital, that is to say, the essence is to use binary digital signals composed of 0 and 1 to represent audio. Mobile phones, computers, computer sound cards, televisions (basically fully digitized), Walkmans, voice recorders, the sound replays and recording equipment we use are all digital audio, no analog audio. In fact, in addition to enthusiasts now, many ordinary people no longer know what analog audio equipment and analog audio media are. Tapes, vinyl records, tape recorders, vinyl turntables, those carriers and equipment that simulate audio have all entered the museum, and there is no intersection with the lives of ordinary people.
In this era of absolute mainstream digital audio, all sound recording and playback equipment, which has a part, a chip, and a circuit, is to do the function of "digital analog conversion". That is, the digital audio signal represented by the 0 and 1 binary signals must be converted into an analog electrical signal. What is an analog electrical signal? What is the biggest difference between it and a digital audio signal? The one-sentence explanation is that the analog audio signal is a continuously changing electrical signal, and if expressed in waveforms, it is a sleek waveform. Digital audio signals have only 0 and 1 states, black and white, and no intermediate states. From an electrical signal perspective, a digital audio signal is a series of pulsed signals, while an analog audio signal is a non-pulsed signal with changing frequencies and intensities.
If we look at the surface of the vinyl record and look at it with a magnifying glass, we can see the actual "ripples" left by the sound. The essence of sound is vibration, and recording the vibration of sound is a series of waveforms. Sound in essence, is "simulated", Edison's original invention of the phonograph and the preservation of sound of the wax cylinder, the principle is to directly record the waveform of the sound, from the Edison era, to the later tape, lp vinyl record, are analog audio era. Why was analog audio later replaced by digital audio? The root cause is that the recording, reproduction and replay of analog audio have serious flaws - all analog recording carriers have a base noise, and each copy and edit introduces new noise and distortion. Even every play can cause wear. After multiple copies and edits of a simulated recording "master", the noise floor becomes large. My college years were the era of the prevalence of cassette tapes, when people who came over, they all knew that every time the tape was copied, the sound quality was obviously deteriorated once, at that time there were "son belts" and "grandson belts", specializing in selling tapes to music fans of professional "brothers", even if they have the original tape, they will not use the original tape to copy, but will first copy a "son belt", and then use the son belt to copy the grandson tape and sell it to music fans. Why? Because every time the original tape is played, the sound quality will also be lost once, and after hundreds of repeated playbacks, the high-frequency response will be significantly deteriorated. The sound quality of the "grandson tape" that fans can buy has been significantly deteriorated compared to the original tape, but the fans at that time could only listen to such things. This is the pain of the analog audio era.
In the era of digital audio, it has been found that digital audio is built on a binary signal composed of 0 and 1, so the copy is loss-free, as long as the data is good, copied countless times, the sound quality will not deteriorate. Digital recorders and CD record players themselves are extremely low-noise, so digital audio is easy to achieve a high signal-to-noise ratio of more than 90 decibels, which solves the noise problem that has plagued people for decades. Due to the non-contact design of the CD head, the playback process is also lossless. So from the 1980s onwards, digital audio with CD as the carrier quickly entered people's lives, and soon replaced analog audio carriers and playback devices. Of course, there are many enthusiasts who are nostalgic for analog carriers such as vinyl records, thinking that their voices are soft, warm, have a "simulated taste", etc., which have the "work" component, and have the psychology of digital audio looking for different things. In the beginning, digital audio replaced analog audio, which was very normal and logical, without any unjust or reluctant elements. From the big picture, although digital audio is not as "natural" as analog audio (the essence of acoustic vibration is the analog waveform), digital audio has great advantages and should completely replace analog audio.
If digital audio is so good, why do you need a "digital-to-analog converter" to convert digital audio into an analog signal? The point is that in the three major parts of the sound system, the amplifier and the horn can still only process the analog audio signal. No matter what is done in front of us, in order for our ears to hear the sound, the horn must also accept the analog electrical signal and vibrate according to the analog electrical signal. If the horn is given a series of pulsed digital signals composed of 0s and 1s, the horn can only emit countless noises. Therefore, the essence of this link of the amplifier is to accept the analog signal and amplify it so that the signal strength reaches the level of enough to drive the horn. The horn link (including headphones) is also completely "analogous", and only by accepting analog audio signals can meaningful sounds be produced.
Therefore, the source must output an analog audio signal to the amplifier. It cannot output digital signals to amplifiers and horns. Therefore, although we are in the era of digital audio, music is recorded, edited, published, circulated, and saved digitally most of the time, when we play music, the playback device (sound source) must output an analog signal so that we can enjoy the music. That is to say, the entire process of recording and replaying is like this - the original musical sound (analog sound wave) - microphone recording (analog mode of electroacoustic conversion, sound waves into a continuous analog electrical signal) - recorded by a digital recorder (in this link the analog electrical signal is converted into a digital signal) - editing, publishing (digital mode) - replay - dac digital-to-analog conversion (conversion to analog audio signal) - amplifier (analog mode) - speaker/headphones (analog sound wave).
Therefore, we know that in all the devices that can play digital audio, from mobile phones, computers, computer sound cards to televisions, Walkmans, Blu-ray machines, all of these devices, which have a part, a line, a chip, are doing the work of "digital-to-analog conversion" (dac), converting digital audio into analog electrical signal output. The "decoder" or DAC that enthusiasts say is only because enthusiasts pay great attention to this part and think that this part has a great impact on sound quality, so they choose a single-function "decoder" product that is loaded into a separate chassis.
The "decoder" or "digital-to-analog converter" or DAC that enthusiasts play is indeed an important source device. It is a typical device with a single function and the supremacy of sound quality. From a functional point of view, it can be said that it has only one function - to convert the input digital audio signal into an analog audio signal output. But in terms of this function, different grades of decoders are completely different, and the styles are different. The decoder is a highly rich and brand-like product in the audio source equipment currently played by enthusiasts. The price ranges from a few hundred pieces to hundreds of thousands of yuan, and there are at least hundreds of brands that are somewhat famous.
All the decoders, looking at the back of it, can see two sets of interfaces. One is digital inputs and the other is analog outputs. The digital signal from the digital source is sent in from the digital input port of the decoder, and when it is working, the signal is output from the analog output port and connected to the rear amplifier link, or the active speaker.
Digital inputs, the most common are four forms - optical, coax, aes/ebu, USB. Among them, the optical fiber port is generally the so-called toslink, there are 3.5 mm round holes and square mouths (can be converted to each other), the desktop is generally a square mouth, and many portable equipment use 3.5 mm round holes. There are two kinds of coaxial ports, rca and bnc (the cable TV cable at home is generally the BNC port, look at the cable TV interface to know what is BNC), so the coaxial line also has rca heads and BNC heads. In fact, the cnc coaxial port has advantages, but most of the equipment is still only equipped with the rca-type coaxial port. Rca-type coaxial port because and single-ended analog port looks exactly the same, some of the initial burn will be confused, in fact, just need to look at one point: the analog rca port must be a pair, divided into left and right (marked l and r), and the digital coaxial port, only one rca port, not divided into left and right.
aes/ebu, commonly known as the "balanced digital mouth", is a three-pin balanced cannon mouth, which is used in professional equipment very much, because it has the advantage of long-distance transmission anti-interference, but it is rare on household equipment. However, if the user's device can be connected through aes/ebu, this is still a priority connection method. USB port, is a digital port that has been popularized in recent years, after all, many people now buy back the decoder, it is connected to the computer through the USB cable to listen to the sound. The way data is exchanged through usb ports and computers has also developed from the early adaptive mode to the current widely popular asynchronous mode. In this mode, the decoder's built-in clock dominates, reducing the degree to which the front-end computer affects the sound.
If a decoder without a usb input – in two cases, an old-fashioned decoder and a very advanced decoder – need to be connected to a computer, then it can be connected through a product called the "usb interface". The computer USB port is connected to the "USB interface", and the USB interface is connected to the decoder through the coaxial or aes/ebu port. I've introduced this kind of stuff before, so you can refer to some old texts.
There are two types of analog outputs for decoders: single-ended rca outputs and balanced xlr outputs. If it is a portable miniature decoder, it may be loaded with a 3.5 mm analog output port. 3.5 mm hole, can be made into a headphone output, can be made into an optical fiber port, can be made into an analog input or output port, due to its small size does not occupy a place, in the portable equipment is very common.
Below is the back of the auralic vega decoder, its interface is very complete, the digital and analog interfaces mentioned earlier have it, everyone recognizes it.
There are a few relatively high-end decoders, in addition to these conventional digital inputs, analog outputs, there is a "clock interface", usually using bnc terminals, here is also mentioned.
Inside all the decoders, inside all the digital audio devices, there's a widget called the clock. Its form can be a separate crystal oscillator, which can be integrated in the chip, but the role is the same, it determines the "time basis" of the entire device when working. We know the principle of digital audio, which is to "sample" the analog signal in continuous variation according to 44.1k hertz (cd specification), or higher frequency (such as 96k Hz), obtain a series of values, and when replaying music, the analog signal must be reconstructed according to this sampling frequency. In this process, the frequency accuracy of sampling and reconstruction is very, very important, which will directly affect whether the reconstructed analog signal is accurate. Therefore, the accuracy of the "clock" within the decoder can significantly affect the sound. Nowadays, many mid-to-high-end decoders use high-precision crystal oscillators. For example, the vega decoder mentioned earlier uses the so-called "femtosecond clock", which has the characteristics of femtosecond precision and extremely low jitter, bringing high sound quality.
However, there is a separate high-end product called "Independent Clock", which is represented by Japanese eoteric products, including the world's most expensive g-0rb super clock with a price of 100,000 yuan. rb is an abbreviation for the metal element rubidium, which uses an observatory-level rubidium atomic clock module, with a well-designed power supply, chassis, suspension, and peripheral circuitry, which can achieve the lowest jitter in the audio equipment. This independent clock device is connected to a decoder with a clock interface via the digital coaxial line of the cnc terminal. Once connected, the signal of the independent clock replaces the clock built into the decoder, so that the decoder can operate according to a higher precision, lower jitter clock. If the digital source and decoder have a clock input interface, then they can all be connected to the same independent clock, which can synchronize the entire audio source system to achieve the best results. Of course, this must be a very advanced system, and the general system below the mid-range cannot be used. The figure below shows that behind the eoteric g0rb, several groups are clock signal outputs of different frequencies.
Regarding "decoder", there are some very common misconceptions that I think need to be clarified, and here are a few of the most classic examples to explain a little.
1) Decoding chip determinism. Many first burners judge the decoder this way: look at what decoding chip is used. If they use a chip that they think is high-grade, a more expensive decoding chip, then they think that the decoder is on the grade; if the decoding chip used is not expensive, then it is dead. On this issue, I have written a special article, I recommend that you take a look: http://blog.sina.com.cn/s/blog_4e2a04300102e6ws.html In fact, there are not many mainstream decoding chips now, such as more and more products using ESS 9018 decoding chips, and manufacturers even have a lite version of the chip supplied to mobile phone manufacturers, so that mobile phones can achieve better sound quality. Recently, the number of manufacturers using Japanese akm decoding chips is also increasing. Some European brands have always favored wolfson's decoding chips. But there's no reason to say that the overall sound quality of a product using the 9018 decoding chip is necessarily better than wolfson. With the same decoder of the 9018 chip, the style and grade of sound can also vary considerably. I don't mean to explain this problem too much, just look at that article. There are multiple determinants of the sound quality and style of the decoder, and it is a systems engineering that is definitely not determined by a chip.
2) Decoder determinism. That is, "as long as the decoder is good, the front can be ignored". The "front" here refers to the device that provides a digital signal to the decoder, or "digital source". It can be a computer sound card, a CD player or a CD turntable, it can be a Walkman device, it can be a Blu-ray machine, any device with a digital output port that can be connected to a decoder. This misunderstanding has a long history, as early as the prevalence of CD players, there are enthusiasts who think that cd players can easily achieve advanced sound quality as long as they are connected to a high-end decoder. Anyway, the digital source only provides a binary digital signal composed of 0 and 1, and it is guaranteed that there will be no errors on the line!
This understanding is completely wrong. A little experienced enthusiasts will find that when playing with equipment, the same decoder, when it is connected to different digital source devices, such as different computer sound cards, different CD turntables, the sound that comes out can be very different. I tried to use a good decoder in front of a super rotten DVD player or a low-end computer sound card as a digital source, and the result was very ugly. Swap the digital source for a good quality CD turntable and the sound immediately becomes very good. Different quality of digital sources, the difference can be very large, can have a "difference between life and death". I repeat, enthusiasts with a little experience with the machine will soon notice this.
The essence of the problem is that when a CD dial is connected to the decoder in an optical fiber or coaxial fashion, the basis of its digital signal is the CD dial's own clock, not the decoder's clock. Even if the clock of the decoder is highly accurate and the grade is high, it can only be "corrected" within a certain range, and it is impossible to completely replace the clock of the previous digital source. When we put a very bad DVD player into a high-level decoder, the digital signal from the DVD player, jitter will be very large, after entering the decoder, although the decoder can lock the signal, in a certain range of this jitter large digital signal to do a little positive correction (according to the decoder's internal high-precision clock), but it can not completely rewrite the clock of the front DVD player, but also have to follow the bad clock, while following, while correcting some. In this system, the jitter that eventually enters the decoding chip's digital signal is determined by the DVD player's clock and the decoder's clock, which are jointly determined by the two clocks, and dominated by the broken clock of the DVD player. Therefore, we must keep in mind that when the digital audio stream is played, the problem caused by the source (poor digital source equipment, high jitter) cannot be completely solved in the later links. If the signal quality from the digital source is already bad, with a high jitter, then the decoder is powerful and the clock accuracy in the decoder is high, it is powerless.
However, there is a case where the decoder's clock will play a dominant role, that is, when transmitting usb asynchronous technology. Most decoders now use the so-called "asynchronous transmission technology" in the USB port, which is dominated by the decoder's clock when exchanging data with the computer. That is to say, as long as the quality of the decoder is high and the internal clock accuracy is good, then the sound quality can be basically ensured, and what computer is used in front of it is not too important. For example, in the architecture of a computer -USB asynchronous transfer-decoder, USB cables, computer system conditions, and computer playback software still affect sound quality, but these factors generally do not become decisive factors.
As mentioned earlier, I will repeat it in simple and practical language: if the digital source is connected to the decoder in an optical fiber and coaxial way, then the output quality of the digital source is very important, and the decoder cannot single-handedly determine the quality of the sound source. A terrible digital source, enough to destroy the best decoder. If the computer connects the decoder in the way of USB asynchronous transmission, then the quality of the decoder itself is the most important, although not the only influencing factor. In any case, conceptually speaking, the decoder is not the only determinant of the sound source, not that as long as the decoder cow, the sound source must be cow; the digital source, the decoder, the connection line, these factors are at work.
Finally, in general, in this era of digital audio, the decoder is still the most important link in the entire "sound source" category, which has the greatest impact on the quality and timbre of sound. Finding and owning a decoder of good quality and style for appetite is an important thing for enthusiasts. In the era we are in, especially streaming media playback (playing audio tracks), there are many forms that can be used: computer + usb decoding, computer sound card + decoding, computer + usb interface + decoding, nas + decoding, stand-alone player, stand-alone player + decoding, Walkman player + decoding, and so on. There may be more streaming forms in the future. In the future of hi-fi streaming, I personally believe that it is a diversified trend, different groups of people play according to their habits, and there will not be an absolute mainstream form. But no matter what form of playback, the decoder is the most important link in the sound source system.
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