1, DSD is very different from current PCM
With the introduction of the Sony Hi-Res Audio concept and the recent launch of some DSD decoding devices, the exposure of DSD seems to be high, and this has also evoked the curiosity of countless enthusiasts. Today, many manufacturers use this as a Promotion and selling point, claiming that DSD has better sound quality. But what is the bottom of the DSD? How big is it compared to traditional audio files? Is it necessary to purchase a device that supports hard-dissolving DSD? Can I use software decoding? Due to the current lack of DSD audio resources and supported devices, DSD is relatively mysterious to most netizens. These problems can be said to be the most concerned at present, and there are many friends who have more or less doubts. These questions, combined with their own views, talk about some things about DSD.
Want to understand DSD first from the PCM to say that DSD has to mention the current use of a wide range of PCM, and our computer commonly used WAV format audio files are encapsulated inside the PCM audio, Apple's OS X system The aiff format is used to store the audio of the packaged PCM. The full name of PCM is Pulse-code modulation. Chinese is pulse code modulation, which is a digital method for audio analog signals. The PCM divides the strength of the signal into segments according to the same spacing and then quantizes it with a unique binary. The process of converting an audio analog signal into a digital signal is a process of modulation, and the process of converting the digital signal back into an analog signal is demodulation.
We all know that the audio signal is an analog signal. The PC used in daily use is a digital device. The internal storage uses digital signals. Therefore, in the digital devices such as PCs, the audio must be digitally stored first, and PCM can be used. Think of it as a solution that converts audio analog signals into digital signals. The red curve in the above picture represents a sine wave, the blue point is the sampling point, the abscissa is the sampling frequency, and the ordinate is the sampling bit depth, so that we can get 9, 11, 12, 13 from the sine wave. , 14 and other data, which can be easily identified by digital devices, this process can be seen as a general principle of PCM coding, but also can explain why we broadcast 24bit or 48kHz in the audio we play every day. parameter. In practical applications, pulse code modulation is certainly not so simple, usually done by a dedicated chip, which is an ADC (analog-to-digital converter).
Of course, after we get these digitized audio signals, we can't simply store them on CDs or hard disks. In order to recognize different specifications of PCM during playback, we need to add certain logos or splits, so we will The PCM is packaged into a WAV or aiff format. Of course, the PCM volume directly sampled by the virtual signal is relatively large, and the PCM is usually compressed. Similar to ape, flac, tta, etc., the result is that the PCM is compressed by lossless coding. And our common MP3, aac, etc. are subject to lossy compression.
The compressed PCM will have many advantages in volume, but the compressed data needs to be decompressed into PCM before playback to decode the DAC chip into an analog audio signal for use by the signal amplifier. Compressed audio encoding and decoding into PCM does not involve the conversion of digital and analog signals, usually through the CPU, and PCM to analog signals requires DAC to complete, and can not be done by the CPU, DAC is not supported Demodulation of any size PCM, the current higher specification PCM can reach 32bit/192kHz, and most of the sound card DAC to support 24bit/192kHz specifications, so the high-standard PCM should be downsampled by the CPU during playback.
Speaking of this, it is generally understood that the conversion between digital signals can be performed by a digitally programmable device such as a CPU, and the conversion between digital and analog signals must be performed through a specially designed DAC or ADC.
2, DSD coding principle and advantages
Now look back at this protagonist DSD, Direct Stream Digital (DSD) is a patented technology of Sony and Philips, it is no wonder that Sony's high-end audio equipment will support. The biggest difference between DSD and our current audio coding format is that it is based on PDM (pulse-density modulation) pulse density modulation, which is completely different from PCM-based audio. PDM expresses the analog audio signal by density. The accuracy of each sampling of PDM is 1 bit. It can be seen from the figure that the position of the sine wave peak is almost 1 and the position of the valley is 0, so it is adjusted by PDM. The audio signal to is not demodulated by the existing PCM-based DAC.
Currently DSD has four different sampling rates of 2.8224MHz (64Fs), 5.6448 MHz (128Fs), 11.2MHz (256Fs) and 22.5792MHz (512Fs). The most used occasion for DSD is Super Audio CD (SACD), which is the source of most DSD audio. The SAD uses a DSD with a sampling rate of 2.8224MHz, while considering the volume requirement in 2005. DDS (Direct Stream Transfer) is also introduced, and DST can also be used directly in SACD.
If you compare the parameters of SACD and CD, you can see that the biggest advantage of SACD is the support of 6-channel audio and the higher response frequency, but I think the response frequency of SACD is not significant because of human hearing. The limit frequency is between 20Hz and 20kHz, and some human ears beyond 20kHz are completely unperceivable. But in terms of bit rate per second, the DSD in SACD reaches 5645kbps, while the average CD is 1411kbps. In theory, DSD records more data than PCM, which can bring more information when demodulated into analog audio signals. Small distortion. If you use a 22.5792MHz DSD, the bit rate per second will double to 45160kbps, which is far from PCM.
Since DSD uses different principles from PCM to modulate, I believe that most parameters of DSD, such as bit depth, sampling rate, etc., are not comparable with PCM, and the author believes that DSD is superior to PCM mainly in the following two points. . The large bit rate of DSD can bring more rich sound details, which is very useful for enthusiasts and the general public, and the frequency response of up to 20Hz-50kHz may not be of great significance to ordinary users.
1. DSD can record more audio data.
2. DSD has a wider frequency response.
Since DSD is better than PCM, why is it not popular? Although DSD is not well-known, it has been 15 years since its launch in 1999. The author thinks that it is mainly because of these four points that DSD popularity is blocked. In the case of DSD, there may be a long way to go before it can be fully popularized. For a long time, DSD is just a plaything for core audiophiles.
1. Consumers lack access to channels. Currently, they can only purchase SACD, which cannot be obtained through the popular online purchase of digital music.
2. There are too few devices that natively support DSD decoding. In most cases, DSD can only be converted to PCM for playback, and the advantages of DSD cannot be experienced.
American Cary Audio DMS-500 player supporting DSD decoding
3. The software that supports DSD is also quite rare. The software rarely supports natively. It needs to install plug-ins, and the playback process is troublesome.
4. DSD is a private patent, and it is difficult for other vendors to follow up.
Compared with PCM, DSD is indeed capable of recording more audio data. In theory, more details can be achieved in the restoration. However, due to lack of hardware, software support and follow-up by other manufacturers, DSD cannot be currently Popularization, even if you have a DAC that supports DSD natively, because SACD has a small circulation, you can't buy the music you want, not to mention the hardware that is supported by the original. There is still a long way to go. It may not be popular in recent years. Therefore, it is recommended that you do not have to blindly purchase equipment that supports DSD in the wild. It may not use its DSD decoding function most of the time. More will still use this device as a traditional device, which is not worth the candle.
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