I believe that some readers have some headaches when they see the professional vocabulary such as "sampling rate, FM synthesis, wavetable synthesis" in the first part. In the second part of the following, I will focus on explaining these professional vocabulary for everyone, and strive to be simple.
1. One of the main functions of the sound sampling sound card is to record and playback sound information. In this process, the number of samples and the sampling frequency determine the quality of sound collection.
1. Sampling digits Sampling digits can be understood as the resolution of the sound card processing sound. The larger the value, the higher the resolution, and the more realistic the recorded and replayed sound.
We must first know that the sound files in the computer are represented by the numbers 0 and 1. So the essence of recording on a computer is to convert analog sound signals into digital signals. Conversely, during playback, the digital signal is restored to an analog sound signal for output. The sound card bit refers to the binary digits of the digital sound signal used by the sound card when collecting and playing sound files. The position of the sound card objectively reflects the accuracy of the description of the digital sound signal to the input sound signal. 8 bits represent 2 to the 8th power-256, and 16 bits represent 2 to the 16th power-64K. In comparison, for a piece of the same music information, a 16-bit sound card can divide it into 64K precision units for processing, while an 8-bit sound card can only process 256 precision units, resulting in a large signal loss. The final sampling effect is naturally Incomparable.
Nowadays, all mainstream products on the market are 16-bit sound cards, not 64-bit or even 128-bit advocated by some ignorant merchants. They confuse the concept of polyphony with the concept of sampling digits. Today's most powerful sound card series-Sound Blaster Live! Although the EMU10K1 chip used is claimed to be 32-bit, it is only a multi-audio streaming technology based on Direct Sound acceleration. Its essence is still a 16-bit sound card. It should be said that 16-bit sampling accuracy is more than enough for computer multimedia audio.
2. Sampling frequency Sampling frequency refers to the number of times the recording device samples the sound signal in one second. The higher the sampling frequency, the more realistic and natural the sound will be. In today's mainstream sound cards, the sampling frequency is generally divided into three levels: 22.05KHz, 44.1KHz, and 48KHz. 22.05 can only achieve the sound quality of FM broadcasting, 44.1KHz is the theoretical CD sound quality limit, and 48KHz is more accurate. . The human ear cannot recognize the sampling frequency higher than 48KHz, so it has little use value on the computer.
Second, the concept of the number of channels The number of channels supported by the sound card is also an important sign of technological development. From mono to the latest surround sound, let's take a closer look.
1. Mono Mono is a relatively original form of sound reproduction, and early sound cards were more commonly used. When playing back mono information through two speakers, we can clearly feel that the sound is transmitted from the middle of the two speakers to our ears. This kind of recording method lacking in position is naturally lagging behind with the current eyes, but when the sound card was just started, it was already a very advanced technology.
2. The stereo mono lacks the positioning of the sound, and the stereo technology has completely changed this situation. The sound is allocated to two independent channels during the recording process, thus achieving a very good sound localization effect. This technique is especially useful in music appreciation. The audience can clearly distinguish the direction from which various instruments come, so that the music is more imaginative and closer to the live experience. Stereo technology is widely used in a large number of sound cards since Sound Blaster Pro, and has become a far-reaching audio standard. Today, stereo is still the technical standard followed by many products.
3. The basic concept of a quasi-stereo quasi-stereo sound card is to use mono when recording sound, and the playback is sometimes stereo and sometimes mono. Sound cards using this technology have been popular on the market for some time, but now they have disappeared.
4. The desire of the four-channel surround people is endless. Although the stereo sound meets the requirements of people for the experience of the location of the left and right channels, with the further development of technology, everyone gradually finds that the two-channel is no longer able to satisfy us. Demand. In the first part of the topic, the author mentioned that the large bandwidth of PCI sound cards has brought many new technologies, among which the most rapid development is the three-dimensional sound effect. The main purpose of the three-dimensional sound effect is to bring people a virtual sound environment, and create a sound field that is more realistic through the special HRTF technology, so as to obtain better game listening effects and sound field positioning (more on this later). To achieve good results, it is not enough to rely on two speakers, so the stereo technology is stretched in front of the three-dimensional sound effect, and the new four-channel surround audio technology solves this problem well.
The four-channel surround specifies four pronunciation points: front left, front right, rear left, and rear right, and the audience is surrounded in the middle. At the same time, it is also recommended to add a subwoofer to enhance the playback processing of low-frequency signals (this is why the 4.1-channel speaker system is widely popular today). As far as the overall effect is concerned, the four-channel system can bring the sound surround from multiple different directions to the listener, can obtain the hearing experience of being in various different environments, and give the user a brand-new experience. Nowadays, four-channel technology has been widely integrated into the design of various high-end sound cards, becoming the mainstream trend in the future.
5.5.1 channel
5.1 channels have been widely used in various traditional theaters and home theaters. Some well-known audio recording compression formats, such as Dolby AC-3 (Dolby Digital) and DTS, are based on the 5.1 sound system as the technical blueprint. In fact, 5.1 sound system comes from 4.1 surround, the difference is that it adds a center unit. This central unit is responsible for transmitting sound signals below 80Hz, which is conducive to enhancing the human voice when watching the film, and concentrates the dialogue in the middle of the entire sound field to increase the overall effect. I believe that everyone who has truly experienced Dolby AC-3 sound effects will be impressed by the 5.1 channel.
Do n’t think that 5.1 is already the pinnacle of surround sound. The more powerful 7.1 system is already eager to try. On the basis of 5.1, it has added two pronunciation points of middle left and middle right, in order to achieve a more perfect state. Of course, due to the relatively high cost, it will take time to become popular, so I won't introduce it here.
3. The concept of three-dimensional sound effects As emerging technologies that many sound cards are pursuing now, let's take a closer look at the mysteries of the three-dimensional sound effects that have been fired.
1.3 The difference and relationship between the audio API and HRTF
API is the meaning of programming interface, which contains many instructions and specifications about sound localization and processing. Its performance will directly affect the expressiveness of 3D sound effects. Today's popular APIs include Direct Sound 3D, A3D, and EAX. HRTF is the English abbreviation of "Head Related Conversion Function", and it is also an important factor for achieving three-dimensional sound effects. Simply put, HRTF is a sound localization algorithm, and its actual role is to deceive our ears. At present, there are many sound chip design manufacturers and research departments in related fields participating in the development and design of this algorithm. Although the principles are similar, but due to the slightly different methods in the analysis and research process, there will be more or less performance differences between various HRTF algorithms. It's easy to confuse API with HRTF. In fact, the two are fundamentally different and related to each other.
To give an example: A3D is one of the most popular 3D audio APIs nowadays, most of the mainstream PCI sound cards now support A3D 1.0. But some users will reflect, why my XXX sound card claims to support A3D, but why the actual effect is not as good as the friend's DIAMOND S90? The reason is that S90 uses Aureal's own AU8820 chip, and the HRTF algorithm used is naturally derived from Aureal; while the XXX sound card does not use the AU8820 chip, but uses other HRTF algorithms, although it can also support A3D function changes, but because of The algorithm is inherently inadequate and needs to be transformed by function. Naturally, it cannot be compared with S90 in effect. Therefore, many sound cards now claim to support A3D, EAX, and DS3D, which can only show that it supports these specifications and instructions. The actual effect depends on the HRTF algorithm used by the chip. Before purchasing a sound card, it is very important to understand what kind of HRTF algorithm its chip uses for the final 3D sound effect.
2. Main 3D audio PAI
(1) Direct Sound 3D-the old audio API derived from Microsoft DirectX. For sound cards that cannot support DS3D, its role is a three-dimensional sound HRTF algorithm that requires CPU, so that these early products have the ability to handle three-dimensional sound. But from the perspective of actual effect and execution efficiency, it is not satisfactory. Therefore, the sound cards introduced thereafter have a so-called "hardware support DS3D" capability. DS3D has become an API interface on this type of sound card, and its actual hearing effect depends on the strength of the HRTF algorithm used by the sound card itself.
(2) A3D——Developed by American Aureal company, it is divided into 1.0 and 2.0. Version 1.0 includes two major application fields of A3D Surround and A3D InteracTIve, with special emphasis on real sound field simulation under stereo hardware environment. 2.0 added sound wave tracking technology on the basis of 1.0 to further enhance performance. It is the best 3D audio technology for positioning today.
(3) EAX-is CREATIVE's new signboard, meaning "environmental sound effect expansion set". EAX is built on DS3D, but several unique sound effect commands are added to the latter. The EAX feature is to focus on rendering various sound changes and performance under different environmental conditions, and the sound positioning ability is not as good as A3D, so EAX recommends that users equip a 4-channel surround speaker system.
3. The main HRTF algorithm.
Large companies such as Aureal and CreaTIve can not only develop powerful instruction set specifications, but also develop advanced HRTF algorithms and integrate them in their own chips. The CRL and QSound introduced below are mainly for the sale and development of HRTF algorithms, and they do not introduce instruction sets.
The HRTF algorithm developed by CRL is called Sensaura and supports most mainstream 3D audio APIs including A3D 1.0 and EAX and DS3D. And this technology has been widely used in ESS, YAMAHA and CMI sound card chips, which has become a relatively influential technology, from the actual audition effect is indeed good. The Q3D developed by QSound can provide an environment simulation function similar to EAX, but the effect is still relatively simple, which is slightly inferior to Sensaura's large and comprehensive performance indicators.
4. About MIDI
MIDI is synonymous with computer music and came out in the early 1980s. What exactly is MIDI? Let us explore together.
1. The concept of MIDI
MIDI is the abbreviation of Musical Instrument Digital Interface, which means the digital interface of music equipment. It is a unified communication protocol between electronic musical instruments and between electronic musical instruments and computers. We can broadly interpret it as a general term for electronic synthesizers and computer music, including protocols, devices, and other related meanings.
2. The essence of MIDI files At present, in some game software and entertainment software, we can often find many music files with MID and RMI extensions. These are the most commonly used MIDI formats on computers. The MIDI file is a descriptive "music language", which expresses the music information to be played in bytes. For example, "At a certain moment, what instrument to use, what note to start with, what tone to end with, what accompaniment to add", etc., so the MIDI file is very compact.
3.FM synthesisSince the MIDI file is just a description of the music, it does not contain any sound information that can be played back, so how is a piece of beautiful computer music played by our sound card? This will require a variety of synthetic means. Earlier ISA sound cards generally used FM synthesis, which is "frequency modulation". It uses the principle of sound oscillation to synthesize MIDI. However, due to the limitations of the technology itself, coupled with the fact that most of these sound cards use cheap YAMAHA OPL series chips, the effect is naturally not good.
4. The English name of the wavetable synthetic wavetable is "WAVE TABLE", which literally translates to "waveform table". In fact, it is to record all the sounds (including various ranges and tones) that can be produced by various real musical instruments and store them as a wave table file. During playback, according to the music information recorded in the MIDI file, a command is given to the wave table, and the corresponding sound information is found one by one from the "table", which is synthesized and processed and played back. Since it uses sampling of real instruments, the effect is naturally better than FM. The sound information of musical instruments of general wavetables is recorded with 44.1KHz and 16Bit precision to achieve the most realistic playback effect. Theoretically, the larger the wave table capacity, the better the synthesis effect.
5. The meaning of polyphony numbers In the naming of various sound cards, we often find numbers such as 64 and 128. Some users and even merchants mistake them for 64-bit and 128-bit sound cards. In fact, as far as the current technological development is concerned, the sound card has not been developed, nor is it necessary to develop such a high data processing channel. 64 and 128 represent only the maximum number of polyphony that this card can achieve during MIDI synthesis. The so-called "polyphony" refers to the maximum number of sounds produced by MIDI music in one second. If the polyphony value supported by the wavetable is too small, some complex MIDI music will have some parts lost during synthesis, which directly affects the playback effect. Fortunately, most wavetable sound cards today provide more than 64 polyphony values, and most MIDI polyphony numbers do not exceed 32, so the phenomenon of timbre loss will not occur.
Another thing to note is the difference between "hardware supports polyphony" and "software supports polyphony". The so-called "hardware-supported polyphony" means that all the polyphony numbers are generated by the sound card chip, and "software-supported polyphony" is to increase the number of polyphony by software synthesis based on the "hardware polyphony", but Need CPU to drive. At present, the largest hardware polyphony supported by mainstream sound cards is 64, while the software polyphony can be as high as 1024, which is amazing!
6. The role of DLS technology
The advent and popularization of PCI sound card brought a little "revolution" of wavetable synthesis, the key lies in the application of DLS technology. DLS is called "Down Loadable Sample", which means: a sample sound library available for download. Its principle is quite similar to that of a soft wave table. It also stores the sound library in the hard disk and transfers it to the system memory when it is played But the difference is that after using DLS technology, it does not use the CPU to calculate when synthesizing MIDI, but relies on the sound card's own audio processing chip for synthesis. The reason is that the data bandwidth of the PCI sound card reaches 133Mb / sec, which greatly widens the system memory. The transmission channel between the sound card and the sound card. This not only eliminates the sound library memory required by the traditional ISA wave table sound card, but also greatly reduces the CPU occupancy rate when playing MIDI. And this wave table library can be updated at any time and use DLS The timbre editing software is modified, which is an advantage that traditional wavetables cannot match.
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