Article 2: deep dive

The audience at the best listening location (sweet spots) can ideally hear all the 3D audio effects, and the sound in other areas will be distorted. In this way, we need to select the correct position when listening. For a pair of speakers, there is a balance, vocal cords, details, three-dimensional sense of the best listening position, called Sweet Spot. Recording and production are always important for listening. Sweet Spot is usually located in the middle of a pair of stereo speakers, several feet ahead. Many experts believe that from the top of the phoneme head to the nose of the speaker, an illusory equedge triangle is the location of Sweet Spot. Due to the influence of many objective conditions, the location may be offset. For example, the reflection on the audio console may affect the speaker, and the speaker differences may also affect the Sweet Spot, some speakers have an optimum location. The actual location is usually determined by continuous audition and adjustment. The wider the scope of the Sweet Spot, the better the effect, which is why developers are trying to extend the coverage of the Sweet Spot.

Figure 5 Multi-speaker Configuration

In a multi-speaker system (4.1, 5.1), the sound is distributed from the speaker around the audience, and the sound is transmitted from different speaker systems, the audience can locate the audio source.

In terms of rules, Panning is enough. e. all speakers play several streams synchronously (depending on the number of speakers), but at different volume levels-the effect is achieved. For example, Dolby Digital uses 6 and 8 audio streams in the 5.1 and 7.1 configurations.

Sensaura MultiDrive, innovative CMSS (innovative multi-speaker surround) technology, able to use four or more speakers to reproduce the sound using the HRTF function.

 Basically, Sensaura MultiDrive3D sound technology must use at least four-channel speakers to express the location of 3D sound effects. The audio content output by each speaker is different. The multi-speaker surround (CMSS) technology of Creative can process any single-channel or stereo sound source to 360 degrees of sound.

Each part of the speaker has two sides. Since the sound field is based on the HRTF function, sweet spot allows the sound source of each side of the audience and the sound source location of the front and back axes to have the best perception. As the coverage of the corners expands, the space for Sweet Spot will become large enough.

Without crosstalk cancellation (CC), it is impossible to locate the audio source. Since HRTF is mainly used for more than four speakers in MultiDrive Technology, it is necessary to apply the CC algorithm to all four speakers, however, this requires the audio processing chip to have very powerful computing capabilities.

After using HRTF, the rear speaker can be precisely positioned like the front speaker. The front speakers are usually placed near the monitor, while the sub-woofer units can be placed on the center floor, while the rear speakers can be placed anywhere the audience prefers, but I believe no one will put it behind me.

Remember, HRTF and CC require very powerful computing power when used in four speaker systems, so manufacturers have come up with a lot of solutions. For example, Aureal has been innovated and acquired to use the Panning algorithm on the rear speaker, because the positioning of the rear speaker is not so strict.

NVIDIA uses Dolby Digital 5.1 in 3D audio. When positioning, the entire audio stream is decoded to the AC-3 format and then delivered to an external decoder in digital format (for example, home theater ).

MIN/large distance, air effect, Macro FX(Min/Max Distance, Air Effects, Macro FX)

Figure 6: Distance Mode

One of the main features of the sound engine is its distance effect. The farther the sound source is, the quieter the sound. The simplest method is to reduce the volume level at a long distance. When the Sound Fades Out, the sound effect designer must assign it a minimum distance. When the sound is within this distance, it only changes its orientation; whenever it crosses a 1-meter distance, the sound intensity will be reduced by 6 dB. Before the farthest distance, the sound will fade, and at last the sound will be too far away to hear. When the sound is close to one volume level, the engine will turn off the sound to release resources. The longer the maximum distance, the longer the sound disappears.

In most cases, the volume level has a logarithm correlation. Designers can identify large and quiet sounds, and the sources can also be differentiated into the minimum and maximum distance. For example, the sound of a mosquito cannot be heard more than 50cm, and the sound of an airplane engine can still be clearly heard several kilometers away.

A3D eax hf roloff

The A3D API expands the distance of DirectSound3D through modular and high-frequency attenuation-similar to the real world, the high-frequency part will be absorbed by the atmosphere according to the corresponding rules-about 0.05dB per meter (selected frequency: 5000Hz by default ). However, in dense weather, air will become more thickened, and high-frequency attenuation will increase. EAX3 allows the processing of low-level Modular Air effects: two reference frequencies-low frequency and high frequency are allocated here, and their effects are based on environmental parameters.

MacroFX

Most HRTF measurements are performed in the remote acoustic field, which simplifies the calculation. However, if the source is within 1 meter (in a nearby area), HRTF cannot fully work. At this time, MacroFX emerged, which is used to reproduce the sound from close areas. The MacroFX algorithm applies to sound in the proximity area, and the sound is positioned as very close to the audience, as if the sound is sent from the speaker to the audience, or even penetrating his/her ears. The effect is based on the precise modularization of acoustic waves transmitted across all spaces around the audience, and data transmission uses efficient algorithms.

The algorithm is integrated into the Sensaura engine and controlled by DirectSound3D, I. e. It is transparent to application developers and can be used to develop a large number of new special effects.

For example, in the flight simulation program, the audience as a pilot can hear the conversation between the air traffic controllers, just as if he was wearing headphones.

Doppler, zoom fx, multiple audience(Doppler, Volumetric Sound Sources (zoom fx), Multiple Listeners)

Doppler effect (Doppler effect): The effective propagation distance between the source and the observation point in the transmission system changes with time, and the observed wave frequency changes. Racing cars or flying games will benefit a lot from the Doppler effect, which can be used in noisy, laser, or plasma shooting, I. e. any target that moves very fast.

Large audio source Effect

The volumetric sources effect allows designers to create large voice sources. You can think like this: the sound of a person running or opening fire with a small weapon is a very small sound source; however, if a group of people are cheering, a huge generator, or a frequent high-speed road, their voices are all in a large area. Compared with the optimal audio source, the larger and merged audio sources can achieve more realistic results.

The optimal sound source can be well applied to large but distant objects, such as mobile cars. In real life, when a car approaches, the audience position will no longer be the best sound source position. However, the DS3D mode algorithm will regard it as the best sound source, and the pictures are not so lifelike (I. e. it looks like a small train approaching rather than a huge train ).

Aureal first applied large audio sources in its A3D API 3.0; then Sensaura added support for large audio sources in its ZoomFX. ZoomFX technology defines several audio sources as a large object (assuming that the sound source of train synthesis can be composed of wheels, engines, coupled carriages, etc ).

Figure 8: Multiple listeners

Multiple listeners (Multiple Listeners) Is a new technology for the gaming console (PlayStation 2, Xbox, GameCube) to support two or more players. For example, in the TV controller PS2 game "gtracing 3" (Polyphony Digital Inc .) supports multiple players, both in different computer and game regions; therefore, they must only hear nearby sounds. Undoubtedly, they can hear each other's voice, but this technology simplifies the implementation process. Unfortunately, there are no hardware APIs to support multiple audiences. This technology is only used in the commercial voice API-FMOD. We will explain its details later.