Why does the computer sound inferior to the CD player?

First of all, does the sound quality of CD machine compare to computer?

This is not necessarily, although the CD machine in the appearance and the computer very different, but its structure is the same, the CPU in the computer is equivalent to the CD machine in the special operation of the chip; the CD-ROM in the computer is equivalent to the turntable system in the CDs machine; The Independent/integrated sound card in the computer is equivalent to the DAC and amp in the CD player. Circuit.

Some people will ask the computer in the function too much, CPU busy, whether will cause the playback quality deterioration? This is not to worry, because from the software point of view, the operating system's "time-sharing" technology is very mature, and universal-even if you have the MP3, also used this technology, think about it--mp3 How do you choose a song, read an electronic novel, play a game, and play music on one side? From the hardware, if interested students can Baidu "latch", it is this device makes playback quality and CPU at the same time how much work almost nothing.

Some people will ask the CPU and CD machine in the special operation processing chip is different, in fact, the difference is relatively large, the CPU's function is limited to general operations, but the CD machine in the Special Operations processing chip is integrated with more functions, such as the DAC and ADC can be taken out alone on the special processing chip, and the latest The IPod shuffle player's dedicated operation Chip even nearly integrates all of the players ' circuitry into the chip's interior, with the outside of a few necessary resistors and no other components.

So what is the difference between the sound quality of a computer and a CD player? It should be said that, if from the level of fairness to the theoretical height, the two output in the digital signal processing phase is no different, but to simulate the signal, there will be some differences.

What is a digital signal? What is a analog signal? If you take a piano piece, the notes recorded on the piano are digital signals, and the piano piano is the analog signal. For the music spectrum, beats how much, the pitch of each note how much, where should be extended, where the rest are recorded clearly, but when the pianist in the performance, it is certainly difficult to ensure that everything in accordance with the harp to play, here we and exclude the pianist is in accordance with their feelings to interpret the music spectrum, But the music playing out of the spectrum, there must be distortion-in accordance with the harp to play in the process caused by the distortion, is just talked about, from digital signals to analog signals between the distortion, which is the computer and CD players play the difference between the quality of the origin.

So why is it that there is no difference in the quality of the audio signal between the computer and the CD player in the digital signal?

Because the content stored on the CD is a digital signal, what is the digital signal? A digital signal is a sequence of 0 and 1. 0 is 0, 1 is 1, whether it is from the optical drive read to the hard disk, or from the network to download to the computer, such a sequence will not change. Just think about it, if a file in the transmission process of 0 and 1 of the disorder, what will be the situation? This means that you upload a picture online and find that the picture is completely different; you send an e-mail to others, the result of that person received the general content of the message is normal, the other half of the content is garbled; You copy one of your documents from C to disk D, and the text in the result is all messed up ... So you think you can say "two identical files, one byte difference is not!" but the quality of the two is different!" What kind of enthusiast is that? Say no, I have to the @ minus second time human flesh crush [1].

According to the unified specification of the CD audio format [3], as set out in the Red Book, simply understand--have you noticed that the tympanic membrane of the speaker is constantly vibrating while the music is playing? The average of one second is divided into 44,100 times, then every 1/44,100 seconds, measuring the position of the tympanic membrane at this time, Convert it to 16 or 0, or a sequence of 1 digits, so that every second you get a series [2] consisting of 44100 x 16 0 or 1, and because this sequence has recorded and constrained the position of the tympanic membrane at that moment, it is the strictest "score". and a "music" record and copy, the transfer process how can be affected by jitter?

"jitter everywhere, do not" can be described as "Senior Burn Friends" cheat new burn Friends of the magic weapon, but if now back to summarize, in the analog sound source of the LP era, LP disc speed does have a great impact on the sound quality played, Because the playback process of analog audio source is like a piano piece from the stylus to the trumpet, moving quickly and slowly does lead to greater distortion; however, in the digital audio CD and MP3 era, the contents of the album has become music rather than directly recorded the piano, the transfer of fast and slow and does not matter, As long as you don't have an impact on the record on the score-you have to ask why I'm sure there's no impact? Think about it, the same piece of paper, with the program code, allows you to properly install an operating system from the disc; Allows you to copy a completely correct picture from a CD without worrying about distortion; So why is the same "sheet music" written in 0 and 1 code, with all sorts of problems copying it from the CD? If you don't point out these " Senior burn Friends "mistakes, you can only continue to watch them slander the digital signal processing field of technicians, experts [4].

The effect on jitter, summed up, is that--jitter is really everywhere, but not omnipotent. In the era of digital audio source, at least in the pure digital signal processing stage, jitter has no effect on the quality of audio signal.

If you make a metaphor, in the era of analog sound sources, music from musicians, equivalent to the entire recording process began, recording as if driving a country road, recording stage, playback stage, has been running on this path, the car has been aging-but in the digital audio source ERA, The engineer paved the highway from the recording stage to the digital analog converter output of the player. Although the car still needs to be high and high, the car can remain as it is on the freeway and keep going. And this high-speed can be CD optical drive, can be a hard disk, can be a network.

Next, the computer and CD-Player quality difference is specifically affected by which aspects?

It has been repeatedly emphasized that the distortion between digital signals and analog signals is the origin of the difference between the sound quality of a computer and a CD player. From the digital signal output, such a sequence of 0, 1 is still the same, but, because ultimately in order to turn this signal into a real sound, we still need to restore the digital signal to analog signals. This process is accomplished by a digital-analog converter (DAC), which is inevitably affected by jitter during the conversion process-but it is important to emphasize that the CD player does not have any advantage over the computer when it comes to countering the distortion caused by the jitter, CD High-grade turntable can be integrated in the circuit board of high-grade crystal oscillator, independent sound card can also be integrated, because the two can be universal; Moreover, the jitter of the distortion caused by it is limited to the refutation of some "burning friends" high-end speech, in fact, jitter The distortion that can be caused is much smaller than other distortions generated by the circuit itself, so that the effects can be ignored.

Compared with the jitter can bring the impact of sound quality, amplification circuit has a significantly greater impact. Because of the technical limitation of the amplification circuit components, the output signal of the digital analog converter can not achieve the ideal linear amplification. In this respect, the high-end CD turntable or can beat the computer-because the high-end CD turntable can have more space to place amplification circuit, electrostatic isolation can be done better than the sound card placed in the chassis. But this is for thousands of yuan and above the high-end products, for portable CD-player, in order to extend its battery power due to the poor endurance time, improve the performance of the amplifier circuit is not the primary goal-the primary goal is how to reduce the power amplifier circuit. And for computers, there's no need to worry about power consumption--certainly not to mention (no one will go crazy to get a pure Class A amp on a computer card), but it's certain that the computer's output power is higher than that of a portable device. Therefore, said that the independent sound quality within the thousand yuan can be "seconds to kill" with the price of the CD and no improper, the same price CD turntable ... Well, I don't quite understand, but are you talking about VCD?

Finally, need to discuss, high-end CD machine relatively low-grade CD machine quality has been improved?

Let's go back to the beginning of the question, there will be some doubt that there are some doubts that the contents of the CD will be able to 100% correctly copied to the computer? Like a lot of scratches on the disc is not it?

Indeed, one less consideration is that it is really difficult to read on discs that already have severe physical wear, and that reading errors are a common problem for poor quality discs. While this is rare for a normally worn disc, it is not. Although the CD standard at the beginning of the formulation, has set a double error correction mechanism, can find the optical drive in the reading disk errors and repair them, but still cannot guarantee that all content can be correctly restored.

So where is the value of the high-end CD turntable? First of all, as mentioned above, the high-end CD turntable as a player as a whole, although in the digital audio source phase and the computer is not very different, but in the process of converting to analog signal has its own unique advantages; On the other hand, when reading a disc with severe physical wear, the upscale CD turntable because of its more sophisticated mechanical structure, design more stable, you can maximize the correct information from the CD-ROM.

But still need to recognize a point, that is relative to the software check code error correction mechanism [5], the mechanics of sophisticated materials and more optimized design play a very small role-to know that even if you read a normal disc, the software's calibration mechanism in the background silently find and fix hundreds of errors every second, Without the guarantee of this mechanism, CD-ROM could hardly be popularized. From this point of view, through mechanical improvements to improve the quality of the poor quality of the CD-ROM, by the way to increase the price of products, is the technical demand-driven, or business interests of operational considerations? I think obviously the latter is more of a component.

The CD Shing is a very important content, although its abstruse degree is not high, now the graduate student Digital signal Processing course has talked about its principle [6], but the most "burning friend" still relies on own imagination to guess the CD decoding process, even has " Burning friend "said that the computer optical drive error correction is by repeatedly reading the same location, see read"0"and"1"which more to judge this position is"0"or"1"--Sadly, this simple and wrong understanding will win the overwhelming majority of" burn friends "agree, really can have a few people can calm down to understand CD Decoding process in order to understand what the real CD error correction mechanism is? The genius-like mechanism devised by the Real Audio field experts and pioneers is simply and rudely misinterpreted [7], and then put on a completely unrelated cloak, driven by commercial interests, The forum composed of enthusiasts from the exchange of true science to pseudoscience rampant, impetuous fever is so like a step by step down.